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Spatial and temporal variation in the diet of the California sea lion (Zalophus californianus) in the Gulf of California, Mexico.

Abstract--Between June 1995 and May 1996 seven rookeries in the Gulf of California Noun 1. Gulf of California - a gulf to the west of the mainland of Mexico
Sea of Cortes

Mexico, United Mexican States - a republic in southern North America; became independent from Spain in 1810
 were visited four times in order to collect scat samples for studying spatial and seasonal variability California sea lion prey. The rookeries studied were San Pedro Martir, San Esteban San Esteban (the Spanish-language name of Saint Stephen) may refer to:
  • Chile
  • San Esteban, Chile
  • Philippines
  • San Esteban, Ilocos Sur
  • Mexico
, El Rasito, Los Machos Machos (Greek: Μάχος, pronunciation: ma-hos), also Mahos is a community in western Ilia in Greece. The population is around 200. Its dialing code is 26230. , Los Cantiles, Isla Granito, and Isla Lobos. The 1273 scat samples collected yielded 4995 otoliths (95.3%) and 247 (4.7%) cephalopod cephalopod (sĕf`ələpŏd'), member of the class Cephalopoda, the most highly organized group of mollusks (phylum Mollusca), and including the squids, octopuses, cuttlefish, and nautiluses.  beaks. Fish were found in 97.4% of scat samples collected, cephalopods in 11.2%, and crustaceans in 12.7%. We identified 92 prey taxa to the species level, 11 to genus genus, in taxonomy: see classification.

Biological classification. It ranks below family and above species, consisting of structurally or phylogenetically (see
 level, and 10 to family level, of which the most important were Pacific cutlassfish (Trichiurus lepturus), Pacific sardine sardine: see herring.

Any of certain species of small (6–12 in., or 15–30 cm, long) food fishes of the herring family (Clupeidae), especially in the genera Sardina, Sardinops, and Sardinella.
 (Sardinops caeruleus), plainfin midshipman midshipman: see toadfish.  (Porichthys spp.), myctophid no. 1, northern anchovy anchovy: see herring.

Any of more than 100 species of schooling saltwater fishes (family Engraulidae) related to the herring. Anchovies are distinguished by a large mouth, almost always extending behind the eye, and by a pointed snout.
 (Engraulis mordax), Pacific mackerel mackerel, common name for members of the family Scombridae, 60 species of open-sea fishes, including the albacore, bonito, and tuna. They are characterized by deeply forked tails that narrow greatly where they join the body; small finlets behind both the dorsal and  (Scomber japonicus), anchoveta (Cetengraulis mysticetus), and jack mackerel (Trachurus symmetricus). Significant differences were found among rookeries in the occurrence of all main prey (P [less than or equal to] 0.04), except for myctophid no. 1 (P>0.05). Temporally, significant differences were found in the occurrence of Pacific cutlassfish, Pacific sardine, plainfin midshipman, northern anchovy, and Pacific mackerel (P<0.05), but not in jack mackerel ([chi square chi square (kī),
n a nonparametric statistic used with discrete data in the form of frequency count (nominal data) or percentages or proportions that can be reduced to frequencies.
]=2.94, df=3, P=0.40), myctophid no. 1 ([chi square]=1.67, df= 3, P=0.64), or lanternfishes ([chi square]=2.08, df=3, P=0.56). Differences were observed in the diet and in trophic trophic /tro·phic/ (tro´fik) (trof´ik) pertaining to nutrition.

Of, relating to, or characterized by nutrition.
 diversity among seasons and rookeries. More evident was the variation in diet in relation to availability of Pacific sardine.


The population of the California sea lion (Zalophus californianus), in the Gulf of California numbers approximately 23,000 individuals, 82% of which inhabit in·hab·it  
v. in·hab·it·ed, in·hab·it·ing, in·hab·its
1. To live or reside in.

2. To be present in; fill: Old childhood memories inhabit the attic.
 the northern region of the gulf above latitude latitude, angular distance of any point on the surface of the earth north or south of the equator. The equator is latitude 0°, and the North Pole and South Pole are latitudes 90°N and 90°S, respectively.  28[degrees] (Aurioles-Gamboa and Zavala-Gonzalez, 1994). In this region are found the most important reproductive areas and the highest pup production of the Gulf. Aurioles-Gamboa and Zavala-Gonzalez (1994) suggested that the high concentration of animals in this region is related to high abundance of pelagic pelagic

living in the middle or near the surface of large bodies of water such as lakes or oceans.
 fish such as Pacific sardine (Sardinops caeruleus) (also known as South American pilchard The South American pilchard, Sardinops sagax, is a sardine of the Family Clupeidae, the only member of the genus Sardinops, found in the indo-Pacific oceans. Their length is up to 40 cm. , FAO FAO,
n See Food and Agriculture Organization.
), Pacific mackerel (Scomber japonicus), Pacific thread herring (Zool.) the gizzard shad. See under Gizzard.

See also: Thread
 (Opisthonema libertate), and anchoveta (Cetengraulis mysticetus) (Cisneros-Mata et al., 1987 (1); Cisneros-Mata et al., 1991 (2); Cisneros-Mata et al., 1997(3)).

Despite the importance of the northern gulf region, feeding studies of the California sea lion at Gulf of California rookeries have been few and have been conducted at different time periods. Researchers have studied sea lion diet in Los Islotes (Aurioles-Gamboa et al., 1984; Garcia-Rodriguez, 1995), Los Cantiles (Isla Angel de la Guarda), Isla Granito (Sanchez-Arias, 1992; Bautista-Vega, 2000), and Isla Racito (Orta-Davila, 1988). These studies have shown that sea lions consume a variety of prey and that differences exist between the diet of sea lions found at different rookeries within the Gulf of California. At Los Islotes, the most important prey were cusk eel cusk eel
Any of several bottom-dwelling, eellike, chiefly marine fishes of the family Ophidiidae.
 (Aulopus bajacali), bigeye big·eye  
Any of several small tropical marine fishes of the family Priacanthidae, having large eyes and reddish scales.

Noun 1.
 bass Pronotogrammus eos), threadfin bass Pronotogrammus multifasciatus), and splitail bass (Hemanthias sp.) (Aurioles-Gamboa et al., 1984; Garcia-Rodriguez, 1995). At Los Cantiles and Isla Granito important prey were lanternfish (Diaphus sp.), northern anchovy (Engraulis mordax), Pacific cutlassfish (Trichiurus nitens), shoulderspot (Caelorinchus scaphopsis), and Pacific whiting (Merluccius productus) (Sanchez-Arias, 1992; Bautista-Vega, 2000), whereas at Isla Racito, important prey were Pacific sardine (Sardinops caeruleus), Pacific mackerel (Scomber japonicus), grunt (Haemulopsis spp.), rockfish rockfish, member of the large family Scorpaenidae (rockfishes and scorpionfishes), carnivorous fish inhabiting all seas and especially abundant in the temperate waters of the Pacific. Rockfishes are found among rocks and reefs.  (Sebastes spp.), and Pacific whiting (Merluccius spp.) (Orta-Davila, 1988).

Some California sea lion prey are important fisheries resources in Mexico. The Pacific sardine, for example, is the target of a fishery begun in 1967 and which, along with the northern anchovy, contributed to most of the volume of the catch (200,870 t during the 1995-96 season) obtained in the Gulf (Cisneros-Mata et al. (3)). The central and northern regions of the Gulf of California harbor the greatest abundance of sea lions and schooling fishes, such as the sardine and anchovy. Because of this, knowledge of sea lion feeding habits and their temporal and spatial variability Spatial variability is characterized by different values for an observed attribute or property that are measured at different geographic locations in an area. The geographic locations are recorded using GPS (global positioning systems) while the attribute's spatial variability is  is relevant to understanding the potential interaction between sea lions and fisheries in the area (Orta-Davila, 1988; Sanchez-Arias, 1992; Bautista-Vega, 2000).

In this article, we present the results of concurrent diet studies conducted at various rookeries and haulout areas of sea lions in the northern rookeries of the Gulf of California to examine the prey consumed, and spatial and temporal variability in their diet.

Materials and methods

Scat samples of California sea lions were collected at Isla San Pedro Martir (SPM SPM - Sequential Parlog Machine , 28[degrees]24'00"N, 112[degrees]25'3"W), Isla San Esteban (EST EST electroshock therapy.

electroshock therapy
, 28[degrees]42'00"N, 112[degrees]36'00"W), Isla Rasito (RAS (1) See network access server.

(2) (Remote Access Service) A Windows NT/2000 Server feature that allows remote users access to the network from their Windows laptops or desktops via modem. See RRAS and network access server.
, 28[degrees]49'30"N, 112[degrees]59'30"W), Isla Granite (GRA GRA Graphic Arts
GRA Grande Raccordo Anulare (circular highway surrounding Rome, Italy)
GRA Graduate Research Assistant
GRA Georgia Research Alliance
GRA Graduate Research Assistantship
GRA Guyana Revenue Authority
, 29[degrees]34'30"N, 113[degrees]32'15"W), Isla Lobes (LOB, 30[degrees]02'30"N, 114[degrees], 28'30"W), and at two colonies of Isla Angel de la Guarda known as Los Machos (MAC, 29[degrees]20'00"N, 113[degrees]30'00"W), and Los Cantiles (CAN, 29[degrees]32'00"N, 113[degrees]29'00"W, Fig. 1). The total number of California sea lions in these seven rookeries was approximately 15,000 animals (that were hauled out) of which about 12.2% inhabit San Pedro Martir, 34.7% San Esteban, 2.8% El Rasito, 10.0% Los Machos, 8.7% Los Cantiles, 11.0% Isla Granite, and 20.6% Isla Lobes (Aurioles-Gamboa and Zavala-Gonzalez, 1994). All the animals were spread out along the shoreline of each island, except at Isla Angel de la Guarda, where they were clustered within two areas: Los Cantiles, on the eastern shoreline and Los Machos on the western shoreline.


Scat samples were obtained at reproductive and non-reproductive haulout areas between June 1995 and May 1996. At El Rasito, sampling was done only at one reproductive area; fresh and dried samples were collected (Fig. 2). If for any reason a scat was not collected (because it was found in pieces or in poor condition), it was destroyed and the site was cleared to avoid collection during subsequent trips. All fresh and dried samples collected were pooled to represent each sampling period. We assumed that the diet information corresponded to a time period close to the collection trip, but some dried scats could have been deposited shortly after the last collection.


Scats were stored in plastic bottles and then dried shortly thereafter to prevent decomposition decomposition /de·com·po·si·tion/ (de-kom?pah-zish´un) the separation of compound bodies into their constituent principles.

 of fish otoliths and other hard parts (which were used in subsequent prey identification) until the scats could be processed at a later date. The samples were processed by soaking in a weak biodegradable biodegradable /bio·de·grad·a·ble/ (-de-grad´ah-b'l) susceptible of degradation by biological processes, as by bacterial or other enzymatic action.

 detergent detergent (dētûr`jənt, dĭ–), substance that aids in the removal of dirt. Detergents act mainly on the oily films that trap dirt particles.  solution for 1 to 7 days before being sifted through nested sieves of 2.00-, 1.18-, and 0.5-mm mesh size. Fish bones and scales, eye lenses of fish and squid, otoliths, cephalopod beaks, and crustacean crustacean (krŭstā`shən), primarily aquatic arthropod of the subphylum Crustacea. Most of the 44,000 crustacean species are marine, but there are many freshwater forms.  fragments were extracted from the samples. Cephalopod beaks were stored in 70% ethanol ethanol (ĕth`ənōl') or ethyl alcohol, CH3CH2OH, a colorless liquid with characteristic odor and taste; commonly called grain alcohol or simply alcohol. , and the other items were dried and stored in vials. Sagittal sagittal /sag·it·tal/ (saj´i-t'l)
1. shaped like an arrow.

2. situated in the direction of the sagittal suture; said of an anteroposterior plane or section parallel to the median plane of the body.
 otoliths and cephalopod beaks were used to identify teleost fish Noun 1. teleost fish - a bony fish of the subclass Teleostei
teleost, teleostan

malacopterygian, soft-finned fish - any fish of the superorder Malacopterygii
 and cephalopods, respectively. Identifications were made by using photographs and diagrams from Clarke (1962), Fitch (1966), Fitch and Brownell (1968), and Wolff (1984), as well as voucher A receipt or release which provides evidence of payment or other discharge of a debt, often for purposes of reimbursement, or attests to the accuracy of the accounts.  specimen material from the 1) Center Interdisciplinario de Marinas Ciencias (CICIMAR), 2) Institute Tecnologico y de Estudios Superiores de Monterrey, Guaymas, 3) Los Angeles County Museum Los Angeles County Museum, Los Angeles, Calif. The original museum opened in 1913. Among its important patrons was William Randolph Hearst, whose enormous collection brought the museum major status among the country's art houses.  of Natural History, California, and 4) Centro de Investigacion Cientifica y de Educacion Superior de Ensenada (CICESE CICESE Centro de Investigacion Cientifica y de Educacion Superior de Ensenada (Spanish) ), Baja California Baja California, state, Mexico
Baja California (Span.: bä`hä kälēfōr`nyä), state (1990 pop. 1,660,855), 27,628 sq mi (71,576 sq km), NW Mexico, on the Baja California peninsula. Mexicali is the capital.
, Mexico. Prey species identifed to family level were coded by using the family name plus a sequential number. Otoliths from prey species that were not identified to species, genus, or family level were coded with "fish species" plus a number.

Three indices were used to describe the diet of sea lions. Percent number (PN) represents the percentage of the number of individuals for each prey taxon taxon (pl. taxa), in biology, a term used to denote any group or rank in the classification of organisms, e.g., class, order, family.  over the total number of individuals found in all scat samples. Percent of occurrence (PO) represents the percentage of scats having a given prey taxon and indicates the percentage of the population that is consuming a particular prey species. The third index, index of importance (IIMP IIMP Integrated Information Management Protocol
IIMP Integrated Information Management Program
) incorporates PN and PO and is defined as

(1) IIM IIM Indian Institute of Management (main Management Institutes of India)
IIM Individual Indian Money (US Department of Interior)
IIM Industrial Information Management
[P.sub.i] = 1/U[U.summation summation n. the final argument of an attorney at the close of a trial in which he/she attempts to convince the judge and/or jury of the virtues of the client's case. (See: closing argument)  over j=1][X.sub.ij]/[X.sub.j],

where [x.sub.i] = number of individuals of taxon i in scat j;

[X.sub.j] = total number of individuals from all taxa found in scat j; and

U = total number of samples with prey.

The IIMP, developed for scat analysis (Garcia-Rodriguez, 1999), was used to determine the importance of prey species, their spatial and temporal variation in the diet, diversity of prey estimates, and measures of similarity among rookeries. Crustaceans were not incorporated into the IIMP index because it was not possible to quantify Quantify - A performance analysis tool from Pure Software.  the number of individuals in the samples.

We used the IIMP Index because it is less sensitive to changes in the number of prey in an individual scat compared to PN. For example, if a scat contains a single prey taxon, the IIMP does not change regardless of the number of individuals of that taxon, in that scat. However, as one increases the number of individuals of a given prey taxon in the scat, the PN will also increase for that prey. The IIMP allows each scat to contribute an equal amount of information, whereas PN can be dominated by a few scats with a large number of a single prey-taxon otoliths. In this manner the IIMP is similar to the split-sample frequency of ocurrence (SSFO SSFO Software Support Field Office
SSFO Self-Storage Fractional Ownership
) index, developed by Olesiuk (1993), where each scat is treated as a sampling unit and does not assume, as does PN, that the distribution of prey hard parts between scats is uniform. However, with the SSFO index, each prey taxon in a given scat is given an equal weight for that scat. If only one species occurs in a sample, its occurrence is scored as 1, if two species occur, each occurrence is scored as 0.5, and so forth (Olesiuk, 1993). The IIMP index incorporates more information than the SSFO index, regardless of the number of individuals of each taxon in the scat. (4)

Percent number (PN) was used only to show differences between broad prey groups (fishes and cephalopods) and PO was used to review the temporal and spatial changes from each main prey (those with average IIMP of at least 10% at any rookery). For all estimations, a single otolith otolith /oto·lith/ (o´to-lith) statolith.

1. Any of numerous minute calcareous particles found in the inner ear of certain lower vertebrates and in the statocysts of many
 (right or left) or single cephalopod beak beak
 or bill

Stiff, projecting oral structure of birds and turtles (both of which lack teeth) and certain other animals (e.g., cephalopods and some insects, fishes, and mammals).
 (upper or lower) represented one individual prey. We tested the hypothesis that the occurrence of the main prey was independent of the rookery and of the date collection using contingency tables and an estimator of chi-square ([chi square]) (Cortes, 1997).

Total length of the otoliths (mm) and the linear equation obtained by Alvarado-Castillo (5) were used to estimate the length of the Pacific sardine (total length mm=7.41+(47.24 x otolith length mm); r=0.85, n=2740). Insufficient data did not allow estimating the size of specimens from May. All estimated lengths were transformed using log10, followed by an ANOVA anova

see analysis of variance.

ANOVA Analysis of variance, see there
 among sampling periods. The size of Pacific sardine consumed by California sea lion was compared to those caught in the commercial fishery. We chose to estimate the size of Pacific sardines because of the broad information available concerning age and growth and other aspects about the fishery and because we found many sardine otoliths in good condition.

Spatial and temporal correlation in composition of diet was compared by using the Spearman spear·man  
A man, especially a soldier, armed with a spear.
 rank correlation In statistics, rank correlation is the study of relationships between different rankings on the same set of items. It deals with measuring correspondence between two rankings, and assessing the significance of this correspondence.  coefficient coefficient /co·ef·fi·cient/ (ko?ah-fish´int)
1. an expression of the change or effect produced by variation in certain factors, or of the ratio between two different quantities.

 ([R.sub.S]) (Fritz fritz  
n. Informal
A condition in which something does not work properly: Our television is on the fritz.

[Perhaps from German Fritz
, 1974). Pairs of IIMP values were used for each prey taxon in a pair of sampling events (rookeries or sampling dates) to examine the correlation among them. This analysis was limited to prey that had an IIMP value of 10% or more. Cluster analysis Cluster analysis

A statistical technique that identifies clusters of stocks whose returns are highly correlated within each cluster and relatively uncorrelated across clusters. Cluster analysis has identified groupings such as growth, cyclical, stable, and energy stocks.
 of average IIMP data for the seven rookeries was used to assess the similarity of the diet among rookeries. The dendrogram A dendrogram is a tree diagram frequently used to illustrate the arrangement of the clusters produced by a clustering algorithm (see cluster analysis). Dendrograms are often used in computational biology to illustrate the clustering of genes.  for the cluster analysis was based on relative Euclidean distances and unweighted pair-grouping methods (UPGMA UPGMA Unweighted Pair Group Method, Arithmetic Mean ) strategy (Ludwig and Reynolds, 1988). We included only prey that, for at least one occasion, had IIMP values [greater than or equal to] 10%.

Trophic diversity was evaluated by using diversity curves (Hurtubia, 1973) developed from IIMP index data. For each date and colony, the cumulative diversity was calculated for increasing numbers of sequentially numbered (but we assumed randomly deposited and collected) scat samples. The diversity curves also allowed us to evaluate sample size (Hurtubia, 1973; Hoffman, 1978; Magurran, 1988, Cortes, 1997) by identifying the point at which the curve flattens. The diversity was estimated by using the Shannon index The Shannon index (incorrectly the Shannon–Weaver index or also incorrectly known as the Shannon-Weiner Index [1]) is one of several diversity indices used to measure diversity in categorical data. :

(2) H' = -[S.summation over i=1][p.sub.i]ln[p.sub.i],

where H' = trophic diversity;

S = total number of prey taxa; and

[P.sub.i] = IIM[P.sub.i], and represents the relative abundance of taxon i obtained from each seat and pooled from scat 1 up to the total number of scats collected.

The values of trophic diversity were then plotted against the number of pooled seats.


Identification of prey

The 1273 scat samples collected during June 1995 through May 1996 (Table 1) yielded fish remains in 97.4% of the samples, cephalopod remains in 11.2%, and crustacean remains in 12.7%. Fish and cephalopods represented 95.3% and 4.7%, respectively, of the 5242 individual prey (excluding crustaceans). The occurrence and number of these prey groups changed temporally and spatially (Fig. 3). We identified 92 prey taxa to the species level, 11 to the genus level, and 10 to family level from 851 scats (Table 2). Remaining scats had damaged prey structures in a condition that prevented us from identifying species to the genus or family level.


We found nine main prey with IIMP average values [greater than or equal to] 10% (Table 3): the Pacific cutlassfish (Trichiurus lepturus), the Pacific sardine (Sardinops caeruleus), the plainfin midshipman (Porichthys spp.), myctophid no. 1, the northern anchovy (Engraulis mordax), Pacific mackerel (Scomber japonicus), the anchoveta (Cetengraulis mysticetus), jack mackerel (Trachurus symmetricus), and the lanternfish (unid. myctophid).

Spatial and temporal variability of the main prey

The importance (IIMP) of the Pacific cutlassfish was greater in Los Cantiles (28.4%), Isla Lobos (20.8%), and Isla Granito (48.5%) than at other sites (Fig. 4). The Pacific sardine was the dominant prey at Los Machos and to the south. There was a significant correlation across the seasons between Los Machos and El Rasito (r=0.998, P=0.04), but not between Los Machos and Isla Granito r=0.602, P=0.59). The IIMP of sardine was also correlated cor·re·late  
v. cor·re·lat·ed, cor·re·lat·ing, cor·re·lates
1. To put or bring into causal, complementary, parallel, or reciprocal relation.

 between El Rasito and San Esteban (r=0.95, P=0.04). The plainfin midshipman did not show a clear pattern, but its presence in the diet increased northeastward from Isla Angel de la Guarda. Lanternfishes, especially myctophid no. 1, were the dominant prey at San Pedro Martir, San Esteban, and El Rasito. The presence of Pacific mackerel was positively correlatcd with the presence of the Pacific sardine. The anchoveta was only found at Isla Lobes, and jack mackerel at El Rasito, San Pedro Martir, and Isla Granito.


The changes in the PO of the main prey coincided with the variations of the IIMP. The occurrence of Pacific cutlassfish, Pacific sardine, plainfin midshipman, northern anchovy, Pacific mackerel, and jack mackerel was significantly different (P<0.04) among rookeries. Myctophid no. 1 showed no significant difference in ocurrence ([chi square]=11.04, df=6, P=0.09); but when all lanternfishes were pooled, their occurrence among rookeries was significantly different ([chi square]=11.13, df=6, P=0.04). We found significant temporal differences in the occurrence of Pacific cutlassfish, Pacific sardine, plainfin midshipman, northern anchovy, and Pacific mackerel (P<0.05), but no significant differences were found among seasons in the occurrence of jack mackerel ([chi square]=2.94, df=3, P=0.40), myctophid no. 1 ([chi square]=1.67, df=3, P=0.6428), or lanternfish ([chi square]=2.08, df=3, P=0.5562).

Size of Pacific sardine consumed by sea lions

The estimated size of the Pacific sardine found in scat was between 101.8 mm and 179.7 mm (mean length of 150.4 mm [+ or -] 13.7 mm). Significant differences were found among sampling periods (F=4.79, df=2, P=0.01), specifically between June and January (Newman-Keuls test; P=0.04) and between September and January (Newman-Keuls test; P=0.01). The average size was 147.4 mm ([+ or -]16.1 mm) in June, 151.7 mm ([+ or -]13.0 mm) in September, and 136.5 mm ([+ or -]13.7 mm) in January (Fig. 5). A similar pattern was found in Los Cantiles, Los Machos, and Isla Granito.


Spatial and temporal correlation in diet

We identified 25 prey taxa that had an IIMP index value of [greater than or equal to] 10% (Table 3) for a given collection. The Spearman rank correlation coefficient of IIMP between any pair of rookeries during June, September, January, and May was not significant (P>0.08). There was no positive correlation Noun 1. positive correlation - a correlation in which large values of one variable are associated with large values of the other and small with small; the correlation coefficient is between 0 and +1
direct correlation
 among any pair of sampling periods for any rookery (P>0.14), except between January and May at San Pedro Martir ([R.sub.S]=0.64, P<0.05) and El Rasito ([R.sub.S]=0.66, P<0.05) and between January and June as well as between January and May at Isla Lobos ([R.sub.S]=0.56, P=0.05; and [R.sub.S]=0.59, P=0.05, respectively).

The similarity in diet was related to the distance between rookeries. A clustering for the seven rookeries was obtained from these 25 prey taxa (Fig 6). We arbitrarily used a "cutoff" distance of 0.3 and 0.4 on the dendrogram as reference points for identifying clusters. The group obtained by using the first distance (0.3) showed four feeding areas: one located in the south (area I: San Pedro Martir, San Esteban, and El Rasito), another in Canal de Ballenas (area II: Los Machos) and two in the north (area III: Los Cantiles and Isla Lobes; and area IV: Isla Granite). When the second distance (0.4) was used, the seven rookeries grouped into two clusters: 1) the southern region and Canal de Ballenas, and 2) the region north of Angel de la Guarda.


Spatial and temporal variability in trophic diversity

Temporal variability in trophic diversity was evident between the rookeries (Fig. 7). In general, two patterns could be differentiated: one in which the diversity varied little throughout the year and the other in which diversity was high in January and low in September. The rookeries San Pedro Martir and Isla Lobos showed the first pattern and Los Machos and Isla Granito (and to a lesser extent, San Esteban and El Rasito) showed the second pattern. In September, when diversity was low, the dominant prey at San Esteban, El Rasito, and Los Machos was Pacific sardine, whereas at Isla Granito, it was Pacific cutlassfish (Fig. 4). The curves obtained for Los Cantiles showed a clear pattern of diversity only in September, although the trend in the January curve would suggest a higher diversity in January than in September.



Stomach acids attack otoliths, affecting their size and number and consequently the estimate of prey occurrence and importance. Erosion of otoliths during digestion digestion

Process of dissolving and chemically converting food for absorption by cells. In the mouth, food is chewed, mixed with saliva, which begins to break down starches, and kneaded by the tongue into a ball for swallowing.
 has been analyzed in studies of pinnipeds in captivity. Bowen (2000) reviewed nine studies that estimated the proportion of otoliths recovered in scat samples to obtain a prey-number correction factor (NCF See National Cristina Foundation. ). He found that NCF is greater than 1.0 because many prey species are not recovered in the scat samples. Additionally, the erosion level can be significantly different among prey species (Bowen, 2000) because of differences in the shape and microstructure mi·cro·struc·ture  
The structure of an organism or object as revealed through microscopic examination.


a structure on a microscopic scale, such as that of a metal or a cell
 of otoliths. Therefore, estimates of biomass based on scat analysis should be carefully interpreted because the consumption of some prey species can be under- or overestimated. Correction factors are needed to compensate for differential erosion for the prey species of each pinniped pinniped: see seal.

Any member of the three existing families of aquatic, fin-footed mammals that constitute the suborder Pinnipedia (order Carnivora; see carnivore).

In this study the most important prey of California sea lions were pelagic fish with small, thin, and fragile otoliths (Nolf, 1993). The lanternfish also have small otoliths--perhaps smaller than those of any other prey taxa found in the scats. Their true importance in California sea lion feeding may be underestimated because of erosion caused by stomach acids (Da Silva sil·va also syl·va  
n. pl. sil·vas or sil·vae
1. The trees or forests of a region.

2. A written work on the trees or forests of a region.
 and Neilson, 1985; Murie and Lavigne, 1985; Jobling and Breiby, 1986; Jobling, 1987; Tollit et al., 1997). Similarly, the presence of cephalopods may have been underestimated because their jaws are composed of chitin, which is harder to digest, and frequently are regurgitated (Pitcher, 1980; Hawes, 1983). However, the high resistance to digestion of cephalopod beaks allows recovery of them in good shape. Thus they are a good choice to use in such diet analyses (Lowry and Carretta, 1999).

A numerical index of prey species importance may over-or underestimate the dominance of prey species in the diet because it does not consider the weight of the prey. For IIMP, a numerical index that assumes a similar weight for all prey species, the true importance of the individual large prey in the diet can be underestimated and the importance of individual small prey can be overestimated. This problem is also present when the PO, PN, and the SSFO index are used because these are all based only upon the number and occurrence of otoliths and cephalopods beaks. As when using PN, and the SSFO, the IIMP does not work for species that cannot be enumerated This term is often used in law as equivalent to mentioned specifically, designated, or expressly named or granted; as in speaking of enumerated governmental powers, items of property, or articles in a tariff schedule. , such as crustaceans.

Given the tendencies of the trophic diversity curves, the sample size was suitable in almost all cases. However, at San Pedro Martir a few more samples would have been useful to fully depict de·pict  
tr.v. de·pict·ed, de·pict·ing, de·picts
1. To represent in a picture or sculpture.

2. To represent in words; describe. See Synonyms at represent.
 the diet. At Los Cantiles, except during September 1995, the samplings should have been more intense because the flattened portion of the diversity curves are not clear. The information, therefore, that comes from those samples could be biased. However, the number of scats that we analyzed contained a high percentage of the consumed species, especially the main prey.

The results of this study indicate that the California sea lion consumed mainly fish and some crustaceans and cephalopods. According to according to
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

 the PN index, fish were more important than cephalopods in the diet of sea lions. In addition, fish were more frequent (PO) than crustacean and cephalopods.

Crustaceans were represented in a similar manner in scats from all rookeries. Cephalopods, however, were more important at San Pedro Martir and San Esteban, probably because they are more common towards the southern gulf. Species of the suborder suborder /sub·or·der/ (sub´or-der) a taxonomic category between an order and a family.

A taxonomic category ranking between an order and a family.
 Oegopsida, which includes oceanic species (Roper and Young, 1975), were most commonly found in scats from these rookeries. Orta-Davila (1988) and Sanchez-Arias (1992) have also noted the low consumption of cephalopods at the northern rookeries. Fish were the most diverse and commonly eaten prey. In contrast to cephalopods, fish were slightly less important in the southern region.

The availability and abundance of the various prey resources influenced the diet of the sea lions in the Gulf of California. The distribution pattern of Pacific sardine closely agrees with its importance in the sea lions diet. The Pacific sardine occurred in high concentrations around Angel de la Guarda and Isla Tiburon during the summer and along

the coast of southern Sonora during the winter, where spawning occurs (Cisneros-Mata et al. (3)). Sardines were consumed in the Canal de Ballenas region during the summer (September), when they are very abundant. Larger size Pacific sardines were consumed by sea lions most frequently during the summer when adult sardines occur more frequently in the Canal de Ballenas. As adult sardine left. Canal de Ballenas (Cisneros-Mata et al., 1997), the proportion of young individuals in the diet of sea lions increased. The fish eaten by sea lions were apparently smaller than those captured by the commercial fisheries. The average estimated size of the sardines consumed was 150.4 mm, whereas the average size of commercially caught fish during the 1995-96 season was 162.4 mm (Cisneros-Mata et al. (3)). This 7% difference in size may have been caused by an underestimation of otolith size because of digestive Ulcers (Digestive) Definition

In general, an ulcer is any eroded area of skin or a mucous membrane, marked by tissue disintegration. In common usage, however, ulcer usually is used to refer to disorders in the upper digestive tract.
 erosion (Jobling and Breiby, 1986). If this is so, then the size of Pacific sardines consumed by sea lions is similar to the size of those captured by the fishery.

Isla Lobos was the only rookery where Pacific sardine was not consumed. This finding differs from those of Cisneros-Mata et al. (3) which show the Pacific sardines present as far north as Isla Lobos. However, their study period was during the 1991-92 El Nino episode, whereas our study occurred during normal oceanographic conditios in 1995-96.

Less is known about the spatial and temporal availability of other important prey. As with commercial captures (Arvizu-Martinez, 1987), Pacific mackerel occurred together with Pacific sardine. Similar variations in occurrence for both species have been noticed from stomach content analyses of the giant squid (Dosidicus gigas) (Ehrhardt, 1991). Lanternfishes were abundant north of Isla Angel de la Guarda (Robison, 1972); however they were not important in the diet of the California sea lion in this region. Their greater importance in the diet at southern rookeries was probably due to the absence of more preferred prey such as Pacific sardine, Pacific cutlassfish, or anchoveta. The consumption of northern anchovy tended to be less important towards Canal de Ballenas, where Pacific sardine reached its maximum importance. The low spatial overlap of these two species has also been noted in other studies. The anchoveta was present only at Isla Lobos. This is an estuarine-lagoon species, typical of coastal lagoons of northern Sinaloa and Sonora (Castro-Aguirre et al., 1995). The presence of this prey in Isla Lobos is possibly due to the sandy coast (Walker, 1960), which is similar to that of the Sinaloa-Sonora coast.

The diet of California sea lions differed among rookeries, probably due to differences in feeding sites and prey availability. Antonelis et al. (1990) studied the foraging characteristics of the northern fur seal The Northern Fur Seal, Callorhinus ursinus, is an eared seal found along the north Pacific Ocean, the Bering Sea and the Sea of Okhotsk. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only species in the genus Callorhinus  (Callorhinus ursinus Callorhinus ursinus

northern fur seal.
) and the California sea lion at San Miguel Island San Miguel Island is the westernmost of California's Channel Islands and the sixth-largest of the eight at 9,325 acres (37.74 km²), including offshore islands and rocks. Prince Island, 700 m off the northeastern coast, measures 35 acres in area.  and found differences between foraging areas among species. The northern fur seal was found most frequently foraging in oceanic water within 72.4 km from the island, whereas Califorinia sea lions forgaged more often in the shallower neritic zone Noun 1. neritic zone - the ocean waters from the low tide mark to a depth of about 100 fathoms
Davy Jones, Davy Jones's locker, ocean bottom, ocean floor, sea bottom, sea floor, seabed - the bottom of a sea or ocean
, within 54.2 km from the island. Different foraging distances in California sea lions from San Miguel Island were found by Melin and DeLong (1999). During the nonbreeding season a higher percentage of foraging locations occurred at distances less than 100 km, whereas during the breeding season Breeding season is the most suitable season usually with favorable conditions and abundant food and water when wild animals and birds (wildlife) have naturally evolved to breed to achieve the best reproductive success.  most of the foraging locations occurred at distances greater than 100 km. These differences are probably due to the increased California sea lion population in San Miguel San Miguel (sän mēgĕl`), city (1993 pop. 118,214), E El Salvador, at the foot of San Miguel volcano (6,996 ft/2,132 m). It has textile, rope, and dairy-products industries. The region produces cotton, henequen, and vegetable oil. ; this increase in population forces sea lions to exploit new areas as a density-dependent response to population growth. Although, these differences could also be due to variability in the distribution of' prey (Melin and DeLong, 1999), as suggested by Antonelis and Fiscus (1980), foraging areas might change with season and annual variations in prey availability and abundance.

Foraging areas in the Gulf of California could lie closer to rookeries than those recorded for San Miguel Island sea lions because the diet was different among rookeries in spite of the shorter distance between them (54.2 km). At Los Islotes, Baja California Sur Baja California Sur (sr), state (1990 pop. 317,764), 27,571 sq mi (71,428 sq km), NW Mexico, on the Baja California peninsula. La Paz is the capital. , adult females fed within 20 km of the colony (Duran-Lizarraga, 1998). Kooyman and Trillmich (1986a, 1986b) reported similar data in sea lion colonies of the Galapagos Islands. In the northern region of the Gulf of California, feeding range could be shorter than that at Los Islotes because of the higher concentration of food at high nutrient nutrient /nu·tri·ent/ (noo´tre-int)
1. nourishing; providing nutrition.

2. a food or other substance that provides energy or building material for the survival and growth of a living organism.
 concentrations (phosphate phosphate, salt or ester of phosphoric acid, H3PO4. Because phosphoric acid is tribasic (having three replaceable hydrogen atoms), it forms monophosphate, diphosphate, and triphosphate salts in which one, two, or three of the hydrogens of the , nitrate nitrate, chemical compound containing the nitrate (NO3) radical. Nitrates are salts or esters of nitric acid, HNO3, formed by replacing the hydrogen with a metal (e.g., sodium or potassium) or a radical (e.g., ammonium or ethyl). , nitrite nitrite

Any salt or ester of nitrous acid (HNO2). The salts are inorganic compounds with ionic bonds, containing the nitrite ion (NO2) and any cation.
, and silicate silicate, chemical compound containing silicon, oxygen, and one or more metals, e.g., aluminum, barium, beryllium, calcium, iron, magnesium, manganese, potassium, sodium, or zirconium. Silicates may be considered chemically as salts of the various silicic acids. ) in Canal de Ballenas that is associated with strong tidal tidal /ti·dal/ (ti´d'l) ebbing and flowing like the waters of the oceans.

Resembling the tides; alternately rising and falling.
 mixing (Alvarez-Borrego, 1983).

Four foraging zones were discerned from dietary differences in sea lions from the seven rookeries studied. Zone I, which included San Pedro Martir, San Esteban, and El Rasito, was characterized by the consumption of lanternfish; zone II, which included Los Machos was characterized by the consumption of Pacific sardine and Pacific mackerel; zone III, which included Isla Granito, by the consumption of Pacific cutlassfish and the northern anchovy; and zone IV, Los Cantiles and Isla Lobos, was characterized by the consumption of the plainfin midshipman and the Pacific cutlassfish. These four zones may indicate differences in habits used by sea lions or may indicate different oceanographic conditions exploited by sea lions. The eastern coast of the Gulf of California displays high photosynthetic pigment A photosynthetic pigment or antenna pigment is a pigment that is present in chloroplasts or photosynthetic bacteria and captures the light energy necessary for photosynthesis.  concentrations, associated with upwelling up·well·ing  
1. The act or an instance of rising up from or as if from a lower source: an upwelling of emotion.

 induced by winds from the northwest in the winter. These conditions may make Canal de Ballenas one of the most important for the distribution of Pacific sardine during the summer.

Trophic diversity varied spatially and temporally. San Pedro Martir and Isla lobos sea lions seem to depend on a more stable feeding areas compared to sea lions at rookeries on Isla Granito and Los Machos, where changes in diversity of consumed species indicated that sea lions feed on fewer species during certain times of the year. Similar results in relation to the changes in diversity were also noticed in the rookeries of the Channel Islands and Farallon Islands The Farallon Islands are a group of islands and rocks found in the Gulf of the Farallones, off the coast of San Francisco, California, USA. They lie 27 miles (43 km) outside the Golden Gate, 20 miles (32 km) south of Point Reyes. They are visible from the mainland on clear days. , California (Bailey and Ainley, 1982; Antonelis et al., 1984; Lowry et al., 1990; Lowry et al., 1991). Perhaps the tendency to have the highest values of diversity and little seasonal variation at San Pedro Martir is the result of this rookery being located in a zone of transition between two biogeographical bi·o·ge·og·ra·phy  
The study of the geographic distribution of organisms.

 areas. This geographical position confers greater environmental heterogeneity het·er·o·ge·ne·i·ty
The quality or state of being heterogeneous.


the state of being heterogeneous.
 and greater ecological diversity (Walker, 1960).

California sea lions in the upper region of the Gulf of California obtain the main portion of their diet from a relatively small number of species. The decrease in abundance of any of these food resources can seriously affect the population, particularly at Isla Granito and Los Machos because sea lions from these rookeries depend on a few species.
Table 1

Number of scats collected at each rookery for each sampling period.

                          June 1995    September 1995    January 1996

San Pedro Martir (SPM)        22             33               88
San Esteban (EST)             50             66               91
El Rasito (RAS)               11             56               58
Los Cantiles (CAN)            20             58               47
Isla Granito (GRA)            24             20               41
Los Machos (MAC)              39             32               36
Isla Lobos (LOB)              72            139               72
Total                        238            404              433

                          May 1996    Total

San Pedro Martir (SPM)        29       172
San Esteban (EST)             67       274
El Rasito (RAS)               25       150
Los Cantiles (CAN)            35       160
Isla Granito (GRA)            19       104
Los Machos (MAC)               0       107
Isla Lobos (LOB)              23       306
Total                        198      1273

Table 2

Prey of California sea lion identified from scat samples collected at
Isla San Pedro Martir, Isla San Esteban, Isla El Rasito, Los Cantiles,
Isla Granito, Los Machos and Isla Lobos from June 1995 through May
1996. n ind. = number of individuals in the sample; PN = percent
number; n occurr = number of occurrences; PO = percentage of
occurrence; IIMP = index of importance.

Scientific name                  Common name                   n Ind.

Trichiurus lepturus              Pacific cutlassfish             306
Sardinops caeruleus              Pacific sardine                 358
Porichthys spp.                  midshipman                      456
Myctophid no. 1                  lanternfish                     714
Engraulis mordax                 northern anchovy                430
Scomber japonicus                Pacific mackerel                103
Cetengraulis mysticetus          anchoveta                       410
Loliolopsis diomedeae            squid                            77
Trachurus symmetricus            jack mackerel                   111
Merlaccius spp.                  Pacific whiting                  55
Pontinus spp.                    scorpionfish                     61
Enoploteuthid no. 1              squid                            95
Caelorinchus scaphopsis          shoulderspot                     65
Octopus sp. no. 1                octopus                          24
Sebastes macdonaldi              Mexican rockfish                 42
Citharichthys sp no. 1           sanddab                         120
Fish species no. 1               --                               49
Haemulopsis leuciscus            white grunt                     176
Peprilus snyderi                 salema butterfish               163
Prionotus spp.                   searobin                         12
Prionotus stephanophrys          lumptail searobin                53
Argentina sialis                 Pacific argentine                19
Fish species no. 2               --                               55
Hemanthias peruanus              splittail bass                   60
Fish species no. 3               --                                9
Micropogonias ectenes            slender croaker                  13
Lepophidium spp.                 cusk-eel                          9
Fish species no. 4               --                               10
Sebastes exsul                   buccanner rockfish               15
Cranchiid no. 2                  Squid                            20
Haemulon flaviguttatum           yellowspotted grunt              11
Selar crumenophthalmus           bigeye scad                      24
Fish species no. 5               --                               33
Paralabrax sp. no. 1             sea bass                          9
Synodus sp. no. 3                lizardfish                       10
Lepophidium prorates             prowspine cusk-eel                5
Fish species no. 6               --                                9
Synodus sp. no. 1                lizardfish                       25
Octopus sp, no. 2                octopus                           8
Gonatus berryi                   squid                             5
Mugil cephalus                   striped mullet                    1
Paranthias colonus               Pacific creole-fish               1
Balistes polylepis               finescale triggerfish            13
Physiculus nematopus             charcoal mora                    30
Hemanthias spp.                  sea bass                          9
Fish species no. 7               --                               10
Uroconger varidens               conger eel                        8
Larimus spp.                     drum                              8
Apogon retrosella                barspot cardinalfish              5
Dosidicus gigas                  squid                             8
Merluccius productus             Pacific whiting                   1
Fish species no. 8               --                                2
Synodus sp. no. 2                lizardfish                       12
Scorpaena sonorae                Sonora scorpionfish               2
Eucinostomus spp.                mojarra                          13
Fish species no. 9               --                                3
Cynoscion reticulatus            striped weakfish                 23
Fish species no. 10              --                               10
Caulolatilus affinis             bighead tilefish                  4
Paralabrax auroguttatus          goldspotted sand bass            18
Fish species no. 11              --                                3
Cranchiid no. 5                  squid                             1
Bodianus diplotoenia             mexican hogfish                   1
Prionotus sp. no. 1              searonbin                         2
Strongylura exilis               california needlefish             1
Synodus spp.                     lizardfish                        6
Fish species no. 12              --                                3
Fish species no. 13              --                                2
Fish species no. 14              --                                3
Fish species no. 15              --                                2
Fish species no. 16                                                2
Porichthys sp. 1                 midshipman                        1
Fish species no. 17              --                                5
Calamus brachysomus              Pacific porgy                     5
Fish species no. 18              --                                1
Fish species no. 19              --                                5
Ophididae no. 1                  --                                1
Fish species no. 20              --                                5
Sebastes sinesis                 blackmouth rockfish               2
Symphurus spp.                   tonguefish                        3
Fish species no. 21              --                                2
Pronotogrammus multifasciatus    threadfin bass                    8
Fsh species no. 22               --                                2
Fish species no. 23              --                                2
Orthopristis reddingi            Bronze-striped grunt             16
Fish species no. 24              --                                2
Fish species no. 25              --                                1
Cranchiidae no. 4                squid                             2
Fish species no. 26              --                                2
Histioteuthis heteropsis         squid                             1
Scorpaenidae no. 1               --                                1
Fish species no. 27              --                                3
Fish species no. 28              --                                1
Fish species no. 29              --                                1
Cranchiidae no. 3                squid                             1
Bollmannia spp.                  goby                              1
Fish species no. 30              --                                1
Cranchiidae no. 1                squid                             1
Paralabrax maculatofasciatus     spotted sand bass                 1
Ophidion scrippsae               basketweave cusk-eel              1
Physiculus spp.                  cod, codling, mora                2
Ophididae no. 2                  --                                4
Unid. Carangidae                 jacks                             8
Unid. Engraulidae                anchovies                         1
Unid. Haemulidae                 grunts                           13
Unid. Labridae                   wrasses                           1
Unid. Mycthophidae               lanternifishes                  216
Unid. Ophididae                  cusk-eel                          2
Unid. Scianidae                  drums                            13
Unid. Scorpaenidae               scorpionfishes                   30
Unid. Serranidae                 sea bass                         13
Unid. Triglidae                  searobins                         1
                                 Unid. Fishes                     39
                                 Unid. Cephalopods                 4
                                 Unid. fishes (very eroded)      381
                                 Remains of cephalopods
                                 Remains of crustaceans

Scientific name                  Common name                     PN

Trichiurus lepturus              Pacific cutlassfish             5.837
Sardinops caeruleus              Pacific sardine                 6.829
Porichthys spp.                  midshipman                      8.699
Myctophid no. 1                  lanternfish                    13.621
Engraulis mordax                 northern anchovy                8.203
Scomber japonicus                Pacific mackerel                1.965
Cetengraulis mysticetus          anchoveta                       7.821
Loliolopsis diomedeae            squid                           1.469
Trachurus symmetricus            jack mackerel                   2.118
Merlaccius spp.                  Pacific whiting                 1.049
Pontinus spp.                    scorpionfish                    1.164
Enoploteuthid no. 1              squid                           1.812
Caelorinchus scaphopsis          shoulderspot                    1.240
Octopus sp. no. 1                octopus                         0.458
Sebastes macdonaldi              Mexican rockfish                0.801
Citharichthys sp no. 1           sanddab                         2.289
Fish species no. 1               --                              0.935
Haemulopsis leuciscus            white grunt                     3.357
Peprilus snyderi                 salema butterfish               3.110
Prionotus spp.                   searobin                        0.229
Prionotus stephanophrys          lumptail searobin               1.011
Argentina sialis                 Pacific argentine               0.362
Fish species no. 2               --                              1.049
Hemanthias peruanus              splittail bass                  1.145
Fish species no. 3               --                              0.172
Micropogonias ectenes            slender croaker                 0.248
Lepophidium spp.                 cusk-eel                        0.172
Fish species no. 4               --                              0.191
Sebastes exsul                   buccanner rockfish              0.286
Cranchiid no. 2                  Squid                           0.382
Haemulon flaviguttatum           yellowspotted grunt             0.210
Selar crumenophthalmus           bigeye scad                     0.458
Fish species no. 5               --                              0.630
Paralabrax sp. no. 1             sea bass                        0.172
Synodus sp. no. 3                lizardfish                      0.191
Lepophidium prorates             prowspine cusk-eel              0.095
Fish species no. 6               --                              0.172
Synodus sp. no. 1                lizardfish                      0.477
Octopus sp, no. 2                octopus                         0.153
Gonatus berryi                   squid                           0.095
Mugil cephalus                   striped mullet                  0.019
Paranthias colonus               Pacific creole-fish             0.019
Balistes polylepis               finescale triggerfish           0.248
Physiculus nematopus             charcoal mora                   0.572
Hemanthias spp.                  sea bass                        0.172
Fish species no. 7               --                              0.191
Uroconger varidens               conger eel                      0.153
Larimus spp.                     drum                            0.153
Apogon retrosella                barspot cardinalfish            0.095
Dosidicus gigas                  squid                           0.153
Merluccius productus             Pacific whiting                 0.019
Fish species no. 8               --                              0.038
Synodus sp. no. 2                lizardfish                      0.229
Scorpaena sonorae                Sonora scorpionfish             0.038
Eucinostomus spp.                mojarra                         0.248
Fish species no. 9               --                              0.057
Cynoscion reticulatus            striped weakfish                0.439
Fish species no. 10              --                              0.191
Caulolatilus affinis             bighead tilefish                0.076
Paralabrax auroguttatus          goldspotted sand bass           0.343
Fish species no. 11              --                              0.057
Cranchiid no. 5                  squid                           0.019
Bodianus diplotoenia             mexican hogfish                 0.019
Prionotus sp. no. 1              searonbin                       0.038
Strongylura exilis               california needlefish           0.019
Synodus spp.                     lizardfish                      0.114
Fish species no. 12              --                              0.057
Fish species no. 13              --                              0.038
Fish species no. 14              --                              0.057
Fish species no. 15              --                              0.038
Fish species no. 16                                              0.038
Porichthys sp. 1                 midshipman                      0.019
Fish species no. 17              --                              0.095
Calamus brachysomus              Pacific porgy                   0.095
Fish species no. 18              --                              0.019
Fish species no. 19              --                              0.095
Ophididae no. 1                  --                              0.019
Fish species no. 20              --                              0.095
Sebastes sinesis                 blackmouth rockfish             0.038
Symphurus spp.                   tonguefish                      0.057
Fish species no. 21              --                              0.038
Pronotogrammus multifasciatus    threadfin bass                  0.153
Fsh species no. 22               --                              0.038
Fish species no. 23              --                              0.038
Orthopristis reddingi            Bronze-striped grunt            0.305
Fish species no. 24              --                              0.038
Fish species no. 25              --                              0.019
Cranchiidae no. 4                squid                           0.038
Fish species no. 26              --                              0.038
Histioteuthis heteropsis         squid                           0.019
Scorpaenidae no. 1               --                              0.019
Fish species no. 27              --                              0.057
Fish species no. 28              --                              0.019
Fish species no. 29              --                              0.019
Cranchiidae no. 3                squid                           0.019
Bollmannia spp.                  goby                            0.019
Fish species no. 30              --                              0.019
Cranchiidae no. 1                squid                           0.019
Paralabrax maculatofasciatus     spotted sand bass               0.019
Ophidion scrippsae               basketweave cusk-eel            0.019
Physiculus spp.                  cod, codling, mora              0.038
Ophididae no. 2                  --                              0.076
Unid. Carangidae                 jacks                           0.153
Unid. Engraulidae                anchovies                       0.019
Unid. Haemulidae                 grunts                          0.248
Unid. Labridae                   wrasses                         0.019
Unid. Mycthophidae               lanternifishes                  4.121
Unid. Ophididae                  cusk-eel                        0.038
Unid. Scianidae                  drums                           0.248
Unid. Scorpaenidae               scorpionfishes                  0.572
Unid. Serranidae                 sea bass                        0.248
Unid. Triglidae                  searobins                       0.019
                                 Unid. Fishes                    0.744
                                 Unid. Cephalopods               0.076
                                 Unid. fishes (very eroded)      7.268
                                 Remains of cephalopods
                                 Remains of crustaceans

Scientific name                  Common name                   Occurr.

Trichiurus lepturus              Pacific cutlassfish             128
Sardinops caeruleus              Pacific sardine                  88
Porichthys spp.                  midshipman                       95
Myctophid no. 1                  lanternfish                     119
Engraulis mordax                 northern anchovy                 43
Scomber japonicus                Pacific mackerel                 42
Cetengraulis mysticetus          anchoveta                        15
Loliolopsis diomedeae            squid                            35
Trachurus symmetricus            jack mackerel                    41
Merlaccius spp.                  Pacific whiting                  25
Pontinus spp.                    scorpionfish                     26
Enoploteuthid no. 1              squid                            23
Caelorinchus scaphopsis          shoulderspot                     25
Octopus sp. no. 1                octopus                          17
Sebastes macdonaldi              Mexican rockfish                 18
Citharichthys sp no. 1           sanddab                          23
Fish species no. 1               --                               25
Haemulopsis leuciscus            white grunt                      21
Peprilus snyderi                 salema butterfish                33
Prionotus spp.                   searobin                          9
Prionotus stephanophrys          lumptail searobin                14
Argentina sialis                 Pacific argentine                13
Fish species no. 2               --                               27
Hemanthias peruanus              splittail bass                   22
Fish species no. 3               --                                6
Micropogonias ectenes            slender croaker                   9
Lepophidium spp.                 cusk-eel                          3
Fish species no. 4               --                                3
Sebastes exsul                   buccanner rockfish               10
Cranchiid no. 2                  Squid                            12
Haemulon flaviguttatum           yellowspotted grunt               3
Selar crumenophthalmus           bigeye scad                      12
Fish species no. 5               --                               19
Paralabrax sp. no. 1             sea bass                          5
Synodus sp. no. 3                lizardfish                        3
Lepophidium prorates             prowspine cusk-eel                4
Fish species no. 6               --                                5
Synodus sp. no. 1                lizardfish                       10
Octopus sp, no. 2                octopus                           7
Gonatus berryi                   squid                             5
Mugil cephalus                   striped mullet                    1
Paranthias colonus               Pacific creole-fish               1
Balistes polylepis               finescale triggerfish             4
Physiculus nematopus             charcoal mora                    12
Hemanthias spp.                  sea bass                          6
Fish species no. 7               --                                8
Uroconger varidens               conger eel                        5
Larimus spp.                     drum                              6
Apogon retrosella                barspot cardinalfish              4
Dosidicus gigas                  squid                             5
Merluccius productus             Pacific whiting                   1
Fish species no. 8               --                                2
Synodus sp. no. 2                lizardfish                        5
Scorpaena sonorae                Sonora scorpionfish               1
Eucinostomus spp.                mojarra                           5
Fish species no. 9               --                                3
Cynoscion reticulatus            striped weakfish                  7
Fish species no. 10              --                                1
Caulolatilus affinis             bighead tilefish                  3
Paralabrax auroguttatus          goldspotted sand bass             4
Fish species no. 11              --                                2
Cranchiid no. 5                  squid                             1
Bodianus diplotoenia             mexican hogfish                   1
Prionotus sp. no. 1              searonbin                         2
Strongylura exilis               california needlefish             1
Synodus spp.                     lizardfish                        5
Fish species no. 12              --                                3
Fish species no. 13              --                                1
Fish species no. 14              --                                1
Fish species no. 15              --                                1
Fish species no. 16                                                2
Porichthys sp. 1                 midshipman                        1
Fish species no. 17              --                                3
Calamus brachysomus              Pacific porgy                     2
Fish species no. 18              --                                1
Fish species no. 19              --                                2
Ophididae no. 1                  --                                1
Fish species no. 20              --                                3
Sebastes sinesis                 blackmouth rockfish               1
Symphurus spp.                   tonguefish                        1
Fish species no. 21              --                                1
Pronotogrammus multifasciatus    threadfin bass                    2
Fsh species no. 22               --                                2
Fish species no. 23              --                                1
Orthopristis reddingi            Bronze-striped grunt              1
Fish species no. 24              --                                1
Fish species no. 25              --                                1
Cranchiidae no. 4                squid                             2
Fish species no. 26              --                                2
Histioteuthis heteropsis         squid                             1
Scorpaenidae no. 1               --                                1
Fish species no. 27              --                                2
Fish species no. 28              --                                1
Fish species no. 29              --                                1
Cranchiidae no. 3                squid                             1
Bollmannia spp.                  goby                              1
Fish species no. 30              --                                1
Cranchiidae no. 1                squid                             1
Paralabrax maculatofasciatus     spotted sand bass                 1
Ophidion scrippsae               basketweave cusk-eel              1
Physiculus spp.                  cod, codling, mora                1
Ophididae no. 2                  --                                1
Unid. Carangidae                 jacks                             3
Unid. Engraulidae                anchovies                         1
Unid. Haemulidae                 grunts                           11
Unid. Labridae                   wrasses                           1
Unid. Mycthophidae               lanternifishes                   71
Unid. Ophididae                  cusk-eel                          1
Unid. Scianidae                  drums                             9
Unid. Scorpaenidae               scorpionfishes                   18
Unid. Serranidae                 sea bass                          6
Unid. Triglidae                  searobins                         1
                                 Unid. Fishes                     16
                                 Unid. Cephalopods                 4
                                 Unid. fishes (very eroded)      231
                                 Remains of cephalopods           14
                                 Remains of crustaceans          162

Scientific name                  Common name                     PO

Trichiurus lepturus              Pacific cutlassfish            15.041
Sardinops caeruleus              Pacific sardine                10.341
Porichthys spp.                  midshipman                     11.163
Myctophid no. 1                  lanternfish                    13.984
Engraulis mordax                 northern anchovy                5.053
Scomber japonicus                Pacific mackerel                4.935
Cetengraulis mysticetus          anchoveta                       1.763
Loliolopsis diomedeae            squid                           4.113
Trachurus symmetricus            jack mackerel                   4.818
Merlaccius spp.                  Pacific whiting                 2.938
Pontinus spp.                    scorpionfish                    3.055
Enoploteuthid no. 1              squid                           2.703
Caelorinchus scaphopsis          shoulderspot                    2.938
Octopus sp. no. 1                octopus                         1.998
Sebastes macdonaldi              Mexican rockfish                2.115
Citharichthys sp no. 1           sanddab                         2.703
Fish species no. 1               --                              2.938
Haemulopsis leuciscus            white grunt                     2.468
Peprilus snyderi                 salema butterfish               3.878
Prionotus spp.                   searobin                        1.058
Prionotus stephanophrys          lumptail searobin               1.645
Argentina sialis                 Pacific argentine               1.528
Fish species no. 2               --                              3.173
Hemanthias peruanus              splittail bass                  2.585
Fish species no. 3               --                              0.705
Micropogonias ectenes            slender croaker                 1.058
Lepophidium spp.                 cusk-eel                        0.353
Fish species no. 4               --                              0.353
Sebastes exsul                   buccanner rockfish              1.175
Cranchiid no. 2                  Squid                           1.410
Haemulon flaviguttatum           yellowspotted grunt             0.353
Selar crumenophthalmus           bigeye scad                     1.410
Fish species no. 5               --                              2.233
Paralabrax sp. no. 1             sea bass                        0.588
Synodus sp. no. 3                lizardfish                      0.353
Lepophidium prorates             prowspine cusk-eel              0.470
Fish species no. 6               --                              0.588
Synodus sp. no. 1                lizardfish                      1.175
Octopus sp, no. 2                octopus                         0.828
Gonatus berryi                   squid                           0.588
Mugil cephalus                   striped mullet                  0.118
Paranthias colonus               Pacific creole-fish             0.118
Balistes polylepis               finescale triggerfish           0.470
Physiculus nematopus             charcoal mora                   1.410
Hemanthias spp.                  sea bass                        0.705
Fish species no. 7               --                              0.940
Uroconger varidens               conger eel                      0.588
Larimus spp.                     drum                            0.705
Apogon retrosella                barspot cardinalfish            0.470
Dosidicus gigas                  squid                           0.588
Merluccius productus             Pacific whiting                 0.118
Fish species no. 8               --                              0.235
Synodus sp. no. 2                lizardfish                      0.588
Scorpaena sonorae                Sonora scorpionfish             0.118
Eucinostomus spp.                mojarra                         0.588
Fish species no. 9               --                              0.353
Cynoscion reticulatus            striped weakfish                0.823
Fish species no. 10              --                              0.118
Caulolatilus affinis             bighead tilefish                0.353
Paralabrax auroguttatus          goldspotted sand bass           0.470
Fish species no. 11              --                              0.235
Cranchiid no. 5                  squid                           0.118
Bodianus diplotoenia             mexican hogfish                 0.118
Prionotus sp. no. 1              searonbin                       0.235
Strongylura exilis               california needlefish           0.118
Synodus spp.                     lizardfish                      0.588
Fish species no. 12              --                              0.353
Fish species no. 13              --                              0.118
Fish species no. 14              --                              0.118
Fish species no. 15              --                              0.118
Fish species no. 16                                              0.235
Porichthys sp. 1                 midshipman                      0.118
Fish species no. 17              --                              0.353
Calamus brachysomus              Pacific porgy                   0.235
Fish species no. 18              --                              0.118
Fish species no. 19              --                              0.235
Ophididae no. 1                  --                              0.118
Fish species no. 20              --                              0.353
Sebastes sinesis                 blackmouth rockfish             0.118
Symphurus spp.                   tonguefish                      0.118
Fish species no. 21              --                              0.118
Pronotogrammus multifasciatus    threadfin bass                  0.235
Fsh species no. 22               --                              0.235
Fish species no. 23              --                              0.118
Orthopristis reddingi            Bronze-striped grunt            0.118
Fish species no. 24              --                              0.118
Fish species no. 25              --                              0.118
Cranchiidae no. 4                squid                           0.235
Fish species no. 26              --                              0.235
Histioteuthis heteropsis         squid                           0.118
Scorpaenidae no. 1               --                              0.118
Fish species no. 27              --                              0.235
Fish species no. 28              --                              0.118
Fish species no. 29              --                              0.118
Cranchiidae no. 3                squid                           0.118
Bollmannia spp.                  goby                            0.118
Fish species no. 30              --                              0.118
Cranchiidae no. 1                squid                           0.118
Paralabrax maculatofasciatus     spotted sand bass               0.118
Ophidion scrippsae               basketweave cusk-eel            0.118
Physiculus spp.                  cod, codling, mora              0.118
Ophididae no. 2                  --                              0.118
Unid. Carangidae                 jacks                           0.353
Unid. Engraulidae                anchovies                       0.118
Unid. Haemulidae                 grunts                          1.293
Unid. Labridae                   wrasses                         0.118
Unid. Mycthophidae               lanternifishes                  8.343
Unid. Ophididae                  cusk-eel                        0.118
Unid. Scianidae                  drums                           1.058
Unid. Scorpaenidae               scorpionfishes                  2.115
Unid. Serranidae                 sea bass                        0.705
Unid. Triglidae                  searobins                       0.118
                                 Unid. Fishes                    1.880
                                 Unid. Cephalopods               0.470
                                 Unid. fishes (very eroded)     27.145
                                 Remains of cephalopods          1.645
                                 Remains of crustaceans         19.036

Scientific name                  Common name                    IIMP

Trichiurus lepturus              Pacific cutlassfish            16.392
Sardinops caeruleus              Pacific sardine                10.020
Porichthys spp.                  midshipman                      9.297
Myctophid no. 1                  lanternfish                     7.901
Engraulis mordax                 northern anchovy                5.199
Scomber japonicus                Pacific mackerel                3.403
Cetengraulis mysticetus          anchoveta                       2.404
Loliolopsis diomedeae            squid                           2.399
Trachurus symmetricus            jack mackerel                   2.273
Merlaccius spp.                  Pacific whiting                 2.206
Pontinus spp.                    scorpionfish                    1.842
Enoploteuthid no. 1              squid                           1.754
Caelorinchus scaphopsis          shoulderspot                    1.728
Octopus sp. no. 1                octopus                         1.614
Sebastes macdonaldi              Mexican rockfish                1.496
Citharichthys sp no. 1           sanddab                         1.220
Fish species no. 1               --                              1.153
Haemulopsis leuciscus            white grunt                     1.093
Peprilus snyderi                 salema butterfish               1.025
Prionotus spp.                   searobin                        0.855
Prionotus stephanophrys          lumptail searobin               0.814
Argentina sialis                 Pacific argentine               0.754
Fish species no. 2               --                              0.737
Hemanthias peruanus              splittail bass                  0.602
Fish species no. 3               --                              0.592
Micropogonias ectenes            slender croaker                 0.547
Lepophidium spp.                 cusk-eel                        0.532
Fish species no. 4               --                              0.511
Sebastes exsul                   buccanner rockfish              0.505
Cranchiid no. 2                  Squid                           0.501
Haemulon flaviguttatum           yellowspotted grunt             0.468
Selar crumenophthalmus           bigeye scad                     0.431
Fish species no. 5               --                              0.384
Paralabrax sp. no. 1             sea bass                        0.373
Synodus sp. no. 3                lizardfish                      0.341
Lepophidium prorates             prowspine cusk-eel              0.335
Fish species no. 6               --                              0.324
Synodus sp. no. 1                lizardfish                      0.324
Octopus sp, no. 2                octopus                         0.308
Gonatus berryi                   squid                           0.274
Mugil cephalus                   striped mullet                  0.265
Paranthias colonus               Pacific creole-fish             0.265
Balistes polylepis               finescale triggerfish           0.245
Physiculus nematopus             charcoal mora                   0.244
Hemanthias spp.                  sea bass                        0.234
Fish species no. 7               --                              0.233
Uroconger varidens               conger eel                      0.189
Larimus spp.                     drum                            0.174
Apogon retrosella                barspot cardinalfish            0.173
Dosidicus gigas                  squid                           0.171
Merluccius productus             Pacific whiting                 0.167
Fish species no. 8               --                              0.159
Synodus sp. no. 2                lizardfish                      0.132
Scorpaena sonorae                Sonora scorpionfish             0.130
Eucinostomus spp.                mojarra                         0.129
Fish species no. 9               --                              0.127
Cynoscion reticulatus            striped weakfish                0.124
Fish species no. 10              --                              0.122
Caulolatilus affinis             bighead tilefish                0.114
Paralabrax auroguttatus          goldspotted sand bass           0.110
Fish species no. 11              --                              0.102
Cranchiid no. 5                  squid                           0.097
Bodianus diplotoenia             mexican hogfish                 0.087
Prionotus sp. no. 1              searonbin                       0.087
Strongylura exilis               california needlefish           0.083
Synodus spp.                     lizardfish                      0.146
Fish species no. 12              --                              0.074
Fish species no. 13              --                              0.065
Fish species no. 14              --                              0.060
Fish species no. 15              --                              0.058
Fish species no. 16                                              0.056
Porichthys sp. 1                 midshipman                      0.052
Fish species no. 17              --                              0.049
Calamus brachysomus              Pacific porgy                   0.043
Fish species no. 18              --                              0.042
Fish species no. 19              --                              0.041
Ophididae no. 1                  --                              0.040
Fish species no. 20              --                              0.039
Sebastes sinesis                 blackmouth rockfish             0.039
Symphurus spp.                   tonguefish                      0.038
Fish species no. 21              --                              0.036
Pronotogrammus multifasciatus    threadfin bass                  0.029
Fsh species no. 22               --                              0.027
Fish species no. 23              --                              0.021
Orthopristis reddingi            Bronze-striped grunt            0.020
Fish species no. 24              --                              0.020
Fish species no. 25              --                              0.016
Cranchiidae no. 4                squid                           0.014
Fish species no. 26              --                              0.014
Histioteuthis heteropsis         squid                           0.014
Scorpaenidae no. 1               --                              0.011
Fish species no. 27              --                              0.011
Fish species no. 28              --                              0.010
Fish species no. 29              --                              0.008
Cranchiidae no. 3                squid                           0.006
Bollmannia spp.                  goby                            0.006
Fish species no. 30              --                              0.005
Cranchiidae no. 1                squid                           0.004
Paralabrax maculatofasciatus     spotted sand bass               0.003
Ophidion scrippsae               basketweave cusk-eel            0.003
Physiculus spp.                  cod, codling, mora              0.003
Ophididae no. 2                  --                              0.002
Unid. Carangidae                 jacks                           0.141
Unid. Engraulidae                anchovies                       0.248
Unid. Haemulidae                 grunts                          0.509
Unid. Labridae                   wrasses                         0.005
Unid. Mycthophidae               lanternifishes                  4.895
Unid. Ophididae                  cusk-eel                        0.098
Unid. Scianidae                  drums                           0.643
Unid. Scorpaenidae               scorpionfishes                  1.078
Unid. Serranidae                 sea bass                        0.176
Unid. Triglidae                  searobins                       0.002
                                 Unid. Fishes                    1.819
                                 Unid. Cephalopods               0.373
                                 Unid. fishes (very eroded)
                                 Remains of cephalopods
                                 Remains of crustaceans

Table 3

Prey of California sea lions having IIMP index values [greater than or
equal to] 10% in at least one sampling period for seven rookeries in
the Gulf of California, Mexico. Blank indicate that species were not
recorded in diet; "--" means unavailable data.

                   Prey species                 June 1995

San Pedro          Engraulis mordax                29.7
Martir             myctophid no. 1                 29.0
                   Porichthys spp.                 11.2
                   Prionotus stephanophrys          0.6
                   enopleoteuthid no. 1
                   Sebastes macdonaldi
                   Haeumulopsis leuciscus
San Esteban        Trichiurus lepturus             24.9
                   Sardinops caeruleus             10.0
                   unid. Myctophidae               13.8
                   myctophid no. 1                  2.8
                   enopleoteuthid no. 1
                   Sebastes macdonaldi
                   fish species no. 1
El Rasito          Porichthys spp.                 26.2
                   unid. Myctophidae               16.4
                   Scomber japonicus               13.8
                   Pontinus spp.                   11.5
                   Octopus sp. no. 1               11.5
                   myctophid no. 1                  6.6
                   Sardinops caeruleus              1.6
                   Trachurus symmetricus
                   Caelorinchus scaphopsis
Los Machos         Sardinops caeruleus             21.0
                   Scomber japonicus               19.0
                   Merluccius spp.                 15.4
                   Trichiurus lepturus             11.7
                   Sebastes macdonaldi              1.8
Los Cantiles       Porichthys spp.                 66.7
                   Trichiurus lepturus             22.2
                   Engraulis mordax                 3.7
                   myctophid no. 1
                   Sardinops caeruleus
                   fish species no. 3
                   unid. Fishes
                   unid. Scianidae
                   Lepophidium spp.
                   Loliolopsis diomedeae
Isla Granito       Engraulis mordax                49.3
                   Trichiurus lepturus             22.0
                   unid. Myctophidae                1.7
                   Sardinops caeruleus              0.9
                   Porichthys spp.                  0.5
                   Cithartchthys sp. no. 1
Isla Lobos         Cetengraulis mysticetus         32.7
                   Trichiurus lepturus             25.2
                   Porichthys spp.                  9.0
                   Loliolopsis diomedeae            4.9
                   Peprilus snyderi

                   Prey species               September 1995

San Pedro          Engraulis mordax
Martir             myctophid no. 1                 10.5
                   Porichthys spp.                  2.0
                   Prionotus stephanophrys          3.3
                   enopleoteuthid no. 1            27.3
                   Sebastes macdonaldi             10.4
                   Haeumulopsis leuciscus
San Esteban        Trichiurus lepturus              3.4
                   Sardinops caeruleus             34.1
                   unid. Myctophidae                3.4
                   myctophid no. 1                 11.8
                   enopleoteuthid no. 1            16.9
                   Sebastes macdonaldi              2.1
                   fish species no. 1
El Rasito          Porichthys spp.                  4.0
                   unid. Myctophidae                1.5
                   Scomber japonicus                3.2
                   Pontinus spp.                    5.1
                   Octopus sp. no. 1
                   myctophid no. 1                  5.1
                   Sardinops caeruleus             40.1
                   Trachurus symmetricus           22.0
                   Caelorinchus scaphopsis          3.6
Los Machos         Sardinops caeruleus             64.1
                   Scomber japonicus
                   Merluccius spp.
                   Trichiurus lepturus              5.4
                   Sebastes macdonaldi
Los Cantiles       Porichthys spp.                 15.5
                   Trichiurus lepturus             38.2
                   Engraulis mordax                 0.4
                   myctophid no. 1                 17.6
                   Sardinops caeruleus              6.8
                   fish species no. 3               0.9
                   unid. Fishes                     0.9
                   unid. Scianidae
                   Lepophidium spp.
                   Loliolopsis diomedeae
Isla Granito       Engraulis mordax                 7.8
                   Trichiurus lepturus             70.1
                   unid. Myctophidae                1.1
                   Sardinops caeruleus
                   Porichthys spp.                 18.2
                   Cithartchthys sp. no. 1
Isla Lobos         Cetengraulis mysticetus          0.1
                   Trichiurus lepturus             27.7
                   Porichthys spp.                 10.3
                   Loliolopsis diomedeae            2.2
                   Peprilus snyderi                23.5

                   Prey species                January 1996

San Pedro          Engraulis mordax                 2.1
Martir             myctophid no. 1                  9.0
                   Porichthys spp.                  6.8
                   Prionotus stephanophrys          3.3
                   enopleoteuthid no. 1             0.8
                   Sebastes macdonaldi
                   Haeumulopsis leuciscus          16.7
San Esteban        Trichiurus lepturus
                   Sardinops caeruleus
                   unid. Myctophidae                4.3
                   myctophid no. 1                  8.9
                   enopleoteuthid no. 1
                   Sebastes macdonaldi              9.7
                   fish species no. 1               1.7
El Rasito          Porichthys spp.                  2.3
                   unid. Myctophidae                8.1
                   Scomber japonicus                3.7
                   Pontinus spp.                    4.1
                   Octopus sp. no. 1                2.9
                   myctophid no. 1                 21.4
                   Sardinops caeruleus              0.9
                   Trachurus symmetricus            5.0
                   Caelorinchus scaphopsis         13.5
Los Machos         Sardinops caeruleus             16.8
                   Scomber japonicus               10.9
                   Merluccius spp.                  8.2
                   Trichiurus lepturus
                   Sebastes macdonaldi             11.3
Los Cantiles       Porichthys spp.
                   Trichiurus lepturus
                   Engraulis mordax                14.3
                   myctophid no. 1                  4.8
                   Sardinops caeruleus             19.0
                   fish species no. 3              14.3
                   unid. Fishes                    19.0
                   unid. Scianidae                 14.3
                   Lepophidium spp.                14
                   Loliolopsis diomedeae
Isla Granito       Engraulis mordax
                   Trichiurus lepturus              2.0
                   unid. Myctophidae               12.6
                   Sardinops caeruleus             18.7
                   Porichthys spp.                  4.6
                   Cithartchthys sp. no. 1         21.7
Isla Lobos         Cetengraulis mysticetus          6.8
                   Trichiurus lepturus             15.8
                   Porichthys spp.                 23.2
                   Loliolopsis diomedeae           11.6
                   Peprilus snyderi                 5.2

                   Prey species                  May 1996

San Pedro          Engraulis mordax                 0.5
Martir             myctophid no. 1                 20.5
                   Porichthys spp.                 15.5
                   Prionotus stephanophrys         10.9
                   enopleoteuthid no. 1
                   Sebastes macdonaldi
                   Haeumulopsis leuciscus           6.0
San Esteban        Trichiurus lepturus              3.0
                   Sardinops caeruleus              4.2
                   unid. Myctophidae               10.9
                   myctophid no. 1                 18.8
                   enopleoteuthid no. 1
                   Sebastes macdonaldi              1.4
                   fish species no. 1              11.0
El Rasito          Porichthys spp.
                   unid. Myctophidae               16.4
                   Scomber japonicus                2.5
                   Pontinus spp.                   10.9
                   Octopus sp. no. 1                7.7
                   myctophid no. 1                  6.8
                   Sardinops caeruleus              7.3
                   Trachurus symmetricus           23.4
                   Caelorinchus scaphopsis         10.5
Los Machos         Sardinops caeruleus              --
                   Scomber japonicus                --
                   Merluccius spp.                  --
                   Trichiurus lepturus              --
                   Sebastes macdonaldi              --
Los Cantiles       Porichthys spp.
                   Trichiurus lepturus             53.1
                   Engraulis mordax
                   myctophid no. 1
                   Sardinops caeruleus
                   fish species no. 3
                   unid. Fishes
                   unid. Scianidae
                   Lepophidium spp.
                   Loliolopsis diomedeae           21.1
Isla Granito       Engraulis mordax
                   Trichiurus lepturus            100.0
                   unid. Myctophidae
                   Sardinops caeruleus
                   Porichthys spp.
                   Cithartchthys sp. no. 1
Isla Lobos         Cetengraulis mysticetus         27.8
                   Trichiurus lepturus             14.3
                   Porichthys spp.                 35.5
                   Loliolopsis diomedeae            3.5
                   Peprilus snyderi

                   Prey species                  Average

San Pedro          Engraulis mordax                 8.1
Martir             myctophid no. 1                 17.3
                   Porichthys spp.                  8.9
                   Prionotus stephanophrys          4.5
                   enopleoteuthid no. 1             7.0
                   Sebastes macdonaldi              2.6
                   Haeumulopsis leuciscus           5.7
San Esteban        Trichiurus lepturus              7.8
                   Sardinops caeruleus             12.1
                   unid. Myctophidae                8.1
                   myctophid no. 1                 10.6
                   enopleoteuthid no. 1             4.2
                   Sebastes macdonaldi              3.3
                   fish species no. 1               3.2
El Rasito          Porichthys spp.                  8.1
                   unid. Myctophidae               10.6
                   Scomber japonicus                5.8
                   Pontinus spp.                    7.9
                   Octopus sp. no. 1                5.5
                   myctophid no. 1                 10.0
                   Sardinops caeruleus             12.5
                   Trachurus symmetricus           12.6
                   Caelorinchus scaphopsis          6.9
Los Machos         Sardinops caeruleus             34.0
                   Scomber japonicus               10.0
                   Merluccius spp.                  7.9
                   Trichiurus lepturus              5.7
                   Sebastes macdonaldi              4.4
Los Cantiles       Porichthys spp.                 20.6
                   Trichiurus lepturus             28.4
                   Engraulis mordax                 4.6
                   myctophid no. 1                  5.6
                   Sardinops caeruleus              6.5
                   fish species no. 3               3.8
                   unid. Fishes                     5.0
                   unid. Scianidae                  3.6
                   Lepophidium spp.                 3.5
                   Loliolopsis diomedeae            5.3
Isla Granito       Engraulis mordax                14.3
                   Trichiurus lepturus             48.5
                   unid. Myctophidae                3.9
                   Sardinops caeruleus              4.9
                   Porichthys spp.                  5.8
                   Cithartchthys sp. no. 1          5.4
Isla Lobos         Cetengraulis mysticetus         16.9
                   Trichiurus lepturus             20.8
                   Porichthys spp.                 19.5
                   Loliolopsis diomedeae            5.6
                   Peprilus snyderi                 7.2


We wish to thank Secretaria de Marina, Armada An earlier brand name for laptop computers from Compaq. The line was noted for its quality and innovative features.  de Mexico, for its great support during the field activities, and the Consejo Nacional de Ciencia y Tecnologia (CONACYT CONACYT Consejo Nacional de Ciencia y Tecnología (National Board of Science and Technology; Mexico, Bolivia, Paraguay) ) for funding this study under grant number 26430-N. The Secretaria de Medio Ambiente, Recursos Naturales y Pesca (SEMARNAP SEMARNAP Secretaria del Medio Ambiente, Recursos Naturales y Pesca (México, Secretariat of the Environment, Natural Resources and Fisheries) ) provided permits for field work (DOO.-700-(2)01104 and DOO.-700(2).-1917). We would like to thank Robert Lavenberg and Jeff Siegel for allowing us the use of otoliths from the collection at the Natural Museum History of Los Angeles Los Angeles (lôs ăn`jələs, lŏs, ăn`jəlēz'), city (1990 pop. 3,485,398), seat of Los Angeles co., S Calif.; inc. 1850.  County and also Lawrence Barnes for his logistical lo·gis·tic   also lo·gis·ti·cal
1. Of or relating to symbolic logic.

2. Of or relating to logistics.

[Medieval Latin logisticus, of calculation
 support during the stay of first author at Los Angeles; we also thank Manuel Nava for allowing us the use of otoliths from the collection in Tecnologico de Monterrey, Campus Guaymas. We are also grateful to Unai Markaida for his assistance in prey identification based on the examination of cephalopods beaks. We thank Mark Lowry fur commenting on an earlier draft of the paper, Norman Silverberg for reviewing the manuscript in English, and two anonymous reviewers fur their valuable suggestions and criticism. The first author would like to thank Centro Interdisciplinario de Ciencias Marinas-IPN for a scholarship (PIFI, Programa Institucional para la Formacion de Investigadores) assigned for postgraduate postgraduate

after first degree graduation, the registerable degree in veterinary science.

postgraduate degree
may be a research degree, e.g. PhD, or a course-work masterate with a vocational bias, or any combination of these.

(1) Cisneros-Mata, M. A., J. P. Santos-Molina, J. A. De Anda M., A. Sanchez-Palafox, and J. J. Estrada. 1987. Pesqueria de sardina en el noroeste de Mexico (1985/86). Informe Tecnico, 79 p. Centro Regional de Investigaciones Pesqueras de Guaymas. INP INP
International News Photo
. SEPESCA SEPESCA Secretariat of Fisheries . Calle 20 No. 605 Sur Col. La Cantera. Guaymas, Son. CP. 85400.

(2) Cisneros-Mata, M. A., M. O. Nevarez-Martinez, G. Montemayor-Lopez, J. P. Santos-Molina, and R. Morales-Azpeitia. 1991. Pesqueria de sardina en el Golfo de California de 1988/89-1989/90. Informe Tecnico, 80 p. Centro Regional de Investigaciones Pesqueras de Guaymas. INP. SEPESCA. Calle 20 No. 605 Sur Col. La Cantera. Guaymas, Son. CP. 85400.

(3) Cisneros-Mata, M. A., M. O. Nevarez-Martinez, M. A. Martinez Zavala, M. L. Anguiano-Carranza, J. P. Santos Santos (sän`ts), city (1996 pop. 412,288), São Paulo state, SE Brazil, on the island of São Vicente in the Atlantic just off the mainland.  Molina, A. R. Godinez-Cota, and G. Montemayor-Lopez. 1997. Diagnosis de la pesqueria de pelagicos menores del Golfo de California de 1991/92 a 1995/96. Informe Tecnico, 59 p. Centro Regional de Investigaciones Pesqueras de Guaymas. INP. SEMARNAP. Calle 20 No. 605 Sur Col. La Cantera. Guaymas, Son. CP. 85400.

(4) Garcia-Rodriguez, F. J., and J. De la Cruz-Aguero. In prep. An index to measure the specie SPECIE. Metallic money issued by public authority.
     2. This term is used in contradistinction to paper money, which in some countries is emitted by the government, and is a mere engagement which represents specie.
 prey importance of California sea lion (Zalophus californianus) based on scat samples.

(5) Alvarado-Castillo, R. Unpubl. data. Departamento de Biologia y Pesquerias, Centro Interdisciplinario de Ciencias Marinas. Avenida IPN IPN Instant Payment Notification (PayPal)
IPN Instituto Politecnico Nacional (México)
IPN Infectious Pancreatic Necrosis
IPN Interplanetary Internet (JPL) 
 S/N (1) (Serial/Number) Common shorthand for serial number.

(2) (Signal/Noise) As in "s/n ratio." See signal-to-noise ratio.
 Col. Palo Playa de Santa Rita, La Paz, Baja California Sur
For other uses, see La Paz (disambiguation).
La Paz is the capital of the Mexican state of Baja California Sur and an important regional commercial center. The city had a 2005 census population of 189,176 persons.
, Mexico 23070.

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National Oceanic and Atmospheric Administration

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 Tech. Rep. NMFS NMFS National Marine Fisheries Service
NMFS National Mortality Followback Survey
NMFS Network Multimedia File System
NMFS Nested Mount File System
 17, 49 p.

Francisco J. Garcia-Rodriguez

David Aurioles-Gamboa

Centro Interdisciplinario de Ciencias Marinas-Instituto Politecnico Nacional

Departamento de Biologia Marina y Pesquerias

Apdo. Postal 592

La Paz, Baja California Sur, Mexico

E-mail address (for F. J. Garcia-Rodriguez):

Manuscript approved for publication 9 October 2003 by Scientific Editor.

Manuscript received 20 October 2003 at NMFS Scientific Publications Office.
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