Patrones de distribucion, fluctuaciones temporales y algunos parametros poblacionales de cuatro especies de lenguados (Pleuronectidae) frente a la costa occidental de baja California.
Fishes of the family Pleuronectidae are widely distributed in subtropical & boreal oceans (Eschmeyer, 1998; Love et al., 2005), and some species constitute important fishery resources in several countries. Of these, Lyopsetta exilis (slender sole) and Microstomus pacificus (dover sole) are among the most abundant flatfishes in the demersal communities of the northwest Pacific Ocean (Alton, 1972; Demory & Hosie, 1975). From the Oregon to Baja California coast, Pleuronectidae are the most abundant softbottom flatfishes caught in otter trawls (Allen, 1982). The available reports on bottom-trawl surveys off southern California lack information on size-specific abundance of soft-bottom species (Allen, 1982; De Martini & Allen, 1984; Love et al., 1986) and most of these surveys sampled depths greater than 12 m.
Besides changes in overall abundance, fish communities can respond to fluctuations in oceanic regimes by showing changes in their geographic or bathymetric distributions (Allen, 2008). These changes in the geographical distribution have been observed often during warm El Nino events. Water depth directly affects the community structure in the continental shelf and slope in coastal waters that potentially serve as nursery areas (Abookire & Norcross, 1998), and depth also plays an important role in determining the distribution of flatfish (Rogers, 1992; Gibson, 1994; Norcross et al., 1995). There is little information about changes in the structure and distribution of flatfish communities during the above mentioned El Nino (Lea & Rosenblatt, 2000; Allen et al., 2004).
Few studies have been reported on Baja California Pleuronectidae, providing general information on the zoogeography (Castro-Aguirre et al., 1992; Eschmeyer, 1998; Rodriguez-Romero et al., 2008) and distribution (Kramer, 1991; Rosales-Casian, 1996; Rabago-Quiroz et al., 2008).
Flatfish species contribute with an account for 88% to demersal fishes captures in Baja California, with more than 500 ton per year (Balart, 1996). Most incidental flatfish captures are taken by otter trawls and such figures indicate the importance of several flatfish species caught in exploratory fishing surveys in Baja California (Ehrhardt et al., 1982; Aurioles-Gamboa et al., 1993).
In the Pacific waters off California and Baja California coasts 22 species of Pleuronectidae have been recognized (Miller & Lea, 1972; Fischer et al., 1995; Eschmeyer, 1998). Exploratory surveys off the western coast of Baja California collected around 20 flatfish species of the families Pleuronectidae, Bothidae, Paralichthyidae and Cynoglossidae (Martinez-Munoz & Ramirez-Cruz, 1992) on the soft bottoms of the continental shelf and slope.
The objectives of this study were: 1) to describe the temporal and spatial patterns in the distribution and abundance of Pleuronectidae; 2) to assess the relationship between abundance and environmental variables that structure flatfish populations; and 3) to determine the population structure for sizes and the characteristics of the size-weight relationships for each of the species studied.
MATERIALS AND METHODS
Study area and data collection
Fishes were collected from April 1988 to September 1990 from nine cruises aboard the R/V El Puma and R/V Marsep XVI. One hundred and five sampling stations were located off the western coast of Baja California, from Boca del Carrizal (23[degrees]00'N) to Vizcaino Bay (28[degrees]51'N) (Fig. 1). Many hours were spent searching for suitable bottoms during the first cruises. Echosonic exploration to detect stations of positive (not risky) trawling, according to bottom outline, was made using a Simrad sounder. Once the geographic position of the stations was established and recorded, the bottom suitability was verified by sampling the type of substrate with a Smith-McIntyre grab. Ships were positioned on the same stations on subsequent trips with a satellite navigator. Samples were taken during day and night. All fishes were collected using an otter trawl 20 m wide and 9 m high at the mouth and, 24 m in length. The nets, in both cases, were those used in the typical shrimp fishery with a stretched mesh size of 3 cm. The mean speed was 2.5 knots. Trawling time and speed were recorded to estimate the area swept by the net (Sparre & Venema, 1997). The trawls were towed for 30 min at depths of 10 m to 250 m.
Temperature and salinity data were recorded after each trawl by using an internally recording conductivity-temperature-depth sound (CTD). The sediment types for the stations were characterized by the percent distribution of sand, silt and clay (Table 1).
Samples were collected according to a random stratified design to cover different depths and geographic regions. Depth sampled comprised inner shelf (10 to 50 m), middle shelf (51 to 100 m) and outer shelf (100 to 250 m depth). Samples were also randomly distributed along geographical regions: Southern (23-24[degrees]N), Central (25-26[degrees]N) and Northern (27-29[degrees]N).
In order to assess both spatial and temporal variations, species abundance data were averaged by sampling region and depth stratum. Bottom water temperature, salinity and bottom sediment composition data were also included in the analysis as a covariable data matrix.
The records of the catches were transformed by area swept, standardized to units of abundance (ind [ha.sup.-1]) and biomass (kg [ha.sup.-1]). Analysis of variance (ANOVA) was used to describe the variability in abundance and biomass by length class, season, region and depth of the stratum. Differences were considered significant where P < 0.05. The Tukey test was used to determine whether there were significant differences among zones and seasons on both fishes and environmental data.
Fishes and environmental data were log (x+1) transformed previously to fulfill homoscedasticity and normality requirements, in order to validate assumption for parametric analyses applied to the univariate and multivariate tests, to reduce the weighting of abundant species, and to balance the effect of different units of measurement of the environmental parameters.
We used redundancy analysis (RDA) to explore species distribution patterns. This technique is a powerful tool to identify patterns of community structure. This ordination analysis technique allows for the establishment of relationships between the community structure pattern and the environmental data pattern and is designed to extract synthetic environmental gradients from ecological data sets (Ter Braak, 1988). The gradients are basic to describe differential habitat preferences of the species via ordination diagrams (Ter Braak & Verdondchot, 1995).
A forward selection of environmental variables was used to select a minimum set of environmental variables that best explained the distribution and abundance of fishes (Ter Braak & Juggins, 1993). The explanatory variables are represented by vectors pointing towards the maximum change in the value of the associated variable. Species and sample sites marked with points would represent the optimum distribution for a given species. The length of each vector on the biplot would indicate the relative importance of the environmental variable in the ordination. The position and direction of each vector indicates how it is correlated with the other vectors and with each axis. To test the advisability of adding variables, Monte Carlo permutation simulations were conducted. Variables were added as long as their addition contributed significantly to explain variance (P < 0.05). Additionally, the Spearman rank correlation coefficient was used to determine the significance of the relationship between each environmental variable and fishes abundance (Zar, 1996).
Environmental characterization of the sampling stations was done through correlation-based Detrended Redundancy Analysis (RDA) using CANOCO 4.5 software (Ter Braak, 1988).
Individual flatfish were identified, counted, measured to the nearest millimetre standard length (SL), weighed (g) and classified into length classes. The relationship between length and weight of fish is described as follows (Wooton, 1990; Anderson & Neumann, 1996):
W = a [SL.sup.b]
where W is weight in grams, SL is the standard length (mm), a-values is the y-intercept and b is the slope.
The length-weight data were grouped by sex, region and shelf stratum and analyzed for possible differences for these factors. To perform the statistical analysis, the length and weight data were logarithmically-transformed (base 10), linear regressions were fitted to pairs of observations by each species and the slopes of the length-weight relationships for these groupings were compared by an analysis of covariance (ANCOVA) to test for equality of slopes among groups.
The surveys represent different oceanic periods: 1988 (ENSO, very warm), 1989 (cold regime), and 1990 (warm regime). These seasonal and interannual fluctuations in the study area were observed in the patterns of temperature, salinity and organic matter concentration (Table 2). The temperature showed values between 13 and 32[degrees]C at the surface, and between 11 and 24[degrees]C at the bottom.
The surface temperature during the fall of 1988 ranged between 21 and 28[degrees]C while it varied between 13 and 24[degrees]C for the summer of 1989 and between 16 and 32[degrees]C for the summer of 1990. The bottom temperature recorded values of 14 to 19[degrees]C, 11 to 22[degrees]C and 11.5 to 24[degrees]C for 1988, 1989 and 1990 respectively.
When ANOVA was applied to the annual values of surface temperature, significant differences between years were found (f = 67.4, df=8, P < 0.05). Significant differences between the inner and outer shelf were also detected for bottom temperatures (F= 4.21, df = 8, P < 0.05). The Tukey test showed also significant differences between the Central and Northern regions.
The temporal variation of salinity recorded the lowest values in the fall of 1988 (28.0 psu) and in the winter of 1988 (30.2 psu), while the highest values were observed in the summer of 1990 (39.2 psu). Statistical analysis showed significant differences (F = 43.6, df = 8, P < 0.05) between the years 1988-1990 and 1989-1990.
Organic matter of the sediments registered the lowest concentrations in the southern region, ranging between 0.3 and 0.9%. In the central region between Punta Abreojos and Magdalena Bay, organic matter concentrations ranged between 0.5 and 4.0%, with a maximum detected near the 100 m isobath. In Vizcaino Bay, the organic matter values ranged between 0.4 and 2.8%.
ANOVA analysis showed that sediment organic matter values were significantly different between the years 1988 and 1990 (F = 6.93, df = 8, P < 0.05). Differences were also significantly different between the north-southern and southern-central region (F = 10.6, df = 8, P < 0.05).
The total abundance of Pleuronectidae was 3166 ind [ha.sup.-1] and biomass was estimated at 143.9 kg [ha.sup.-1]. Four species of the family Pleuronectidae were found: Pleuronichthys ritteri (spotted turbot); P. verticalis (hornyhead turbot); Lyopsetta exilis (slender sole) and Microstomus pacificus (Dover sole).
The most abundant species was spotted turbot accounting to 78.1% in abundance and 73.8% in biomass of the total catches, being present in more than 60% of the samples. Second in abundance was slender sole with 16% in numbers and 18.5% in biomass, with an ocurrence of 10.6%. Hornyhead turbot and dover sole showed values less than 3% of the abundance and 6% biomass, respectively, but the former accounted for 20% occurrence in the sampling.
Spotted turbot was widely distributed throughout the three regions off the western coast of Baja California. Spatial and temporal relative abundances changed throughout the three-year studied period. During 1988-1989 fishes were more abundant in the southern (1653 ind [ha.sup.-1] and 63.0 kg [ha.sup.-1]) and central (663 ind [ha.sup.-1] and 36.8 kg [ha.sup.-1]) regions. The northern region recorded the minimum abundances with a mean of 156 ind [ha.sup.-1] and 6.4 kg [ha.sup.-1] (Figs. 2a, 2c).
The depth distribution of spotted turbot had the highest abundances in the inner and middle stratum, with 904 ind [ha.sup.-1] and 1033 ind [ha.sup.-1], respectively, with the corresponding biomass values ranging between 62.3 and 31.2 kg [ha.sup.-1]. The minimum values were found in the outer shelf with 505 ind [ha.sup.-1] and 12.6 kg [ha.sup.-1] (Figs. 2b, 2d).
The contours of highest abundance (Fig. 3a) ranged between 156 and 786 ind [ha.sup.-1], in April-July 1988 and 1989 respectively, in the localities of San Ignacio Lagoon and San Juanico Bay, and the waters adjacent to Cape San Lazaro and Margarita Island (center).
In the middle and shallow strata of Vizcaino Bay hornyhead turbot (Fig. 3b) recorded the highest abundances in March 1990, with 61 ind [ha.sup.-1] and 4.6 kg [ha.sup.-1]. Lower values were found between the localities of Bahia San Juanico and San Ignacio Lagoon with 32 ind [ha.sup.-1] and 3.4 kg [ha.sup.-1] respectively. The lowest values of biomass and abundance were found close to Magdalena Bay 3 ind [ha.sup.-1] and 0.21 kg [ha.sup.-1] (Figs. 2a 2d).
Slender sole record their peak abundance of 500 ind [ha.sup.-1] and a biomass of 130 kg [ha.sup.-1] in Vizcaino Bay, at depths between 90 and 200 m (Figs. 2a-2d). The highest abundance values ranged between 8 and 12 ind [ha.sup.-1] in September 1990. The minimum abundance was 6 ind [ha.sup.-1] in San Juanico Bay and Vizcaino Bay, at depths less than 50 m in March and September 1990 (Fig. 3c).
The highest abundance of Dover sole was found in Vizcaino Bay: 93 ind [ha.sup.-1], with a biomass of 2.8 kg [ha.sup.-1] (Figs. 2a-2d).). The highest values of abundance of 79 ind [ha.sup.-1] were observed in July 1989, at depths between 80 and 134 m. The lowest abundance was 2 ind [ha.sup.-1] in March and September 1990 (Fig. 3d).
Dominant Pleuronectidae fishes showed average sizes ranging from 45 to 261 mm. Species composition varied spatially, with the most abundant species shifting in rank depending on the zone. Turbots were more abundant in the inner zone, while slender and dover sole were more abundant in the outer zone. The correlation coefficients between the environment variables and the ordination axes reflect the relative importance of each environmental variable in determining the structure of the Pleuronectidae assemblages. Using the Monte Carlo permutation test, we selected explanatory variables of region, shelf strata, salinity, sediment type (clay, sand, and silt), organic matter, surface and bottom temperature, at the 99% (P < 0.01) significance level.
Thus, Axis 1 corresponds to the northern region, inner and external shelf, surface and bottom temperature, sand, silt and clay, while Axis 2 corresponds to the salinity gradient. The species and environment correlation coefficients were 0.48 for Axis 1 and 0.4 for Axis 2 (Table 3).
The ordination diagram from the first two axes (Fig. 4), with samples coded by depth stratum, showed changes in the Pleuronectidae assemblages from the inner to the outer zone. Axis 1 explained 80.4% of the variance of the relationship between species and environment parameters (region, sediment type and depth gradient). The outer shelf associated with the deeper stations and, sediments with high concentrations of silt and organic matter. By contrast, the inner shelf was associated with sandy sediments.
Species associated with Axis 1 were slender sole and dover sole, while spotted turbot is located on the right side. Axis 2, explains 95.3% of the variance for the relationship between species and the environmental factors salinity and surface and bottom temperatures. Spotted turbot, related to Axis 2, is associated with stations located in the cold waters of the middle and outer shelf.
The spotted turbot population of 1988 included juveniles and adults within a wide range of sizes between 55 mm to 270 mm SL (Fig. 5a). Sizes ranged between 90 and 175 mm standard length (SL) in the southern region and between 75 to 180 mm in the central region. For 1989, the sizes ranged between 70 and 261 mm SL in the southern region and between 45 and 188 mm in the northern region.
For 1990, the corresponding values were 100-210 mm in the south and 140-155 mm in the north. ANOVA was applied to compare size classes according to the region, resulting in significant differences (F = 37.4, df = 420, P < 0.05). However, the Tukey's test did not show significant differences between regions.
The length of hornyhead turbot ranged between 100 and 187 mm SL. The record was wider in the summer of 1990 and included juveniles and adults (Fig. 5b). The narrower range (150-180 mm) was recorded during the winter of 1989. The sizes observed in slender sole ranged between 75 and 200 mm, and included many juveniles during summer 1989 (Fig. 5c). Dover sole was represented mainly by juveniles in the range 90 to 185 SL mm (Fig. 5d).
The sex ratio of Pleuronectidae was close to 1:1, except for spotted turbot (1:1.4). Length-weight equations for all species were highly significant (P < 0.001) for combined sex, male and female samples (Table 4).
Males showed an exponent (b) greater than females, except in hornyhead turbot. For the overall sample of Pleuronectidae, the exponent exceeds the value of 3, except for dover sole, which showed a slightly lower value.
The weight-length relationship for the flatfish in the study area showed significant correlation between these parameters ([r.sup.2] = 0.9), as shown in Table 4.
The hypothesis of isometric growth for this species was discarded, as the allometric index value (b) was significantly different from 3 (Student's t-test, P < 0.05). Length and weight were closely correlated with the determination coefficients ranging from 0.80 to 0.97 in both sexes, which indicated a strong relationship between these two variables except for males of slender sole.
Significant differences between sexes were found for the slopes of the weight/length relationship in the cases of spotted turbot and hornyhead turbot. Females of hornyhead turbot were slightly heavier than males of the same length, whereas the spotted turbot presented the opposite pattern. No significant differences between sexes were found for slender sole ordover sole, perhaps because their populations were composed mainly of young individuals.
Comparing the slopes for different years, only spotted turbot showed significant differences between 1988 and 1990. Comparing regions, it was found that slopes were different in spotted turbot in all three regions, while slopes for hornyhead turbot were significantly different between the central and northern regions. Moreover, when the slopes were compared for depth strata, significant differences between the inner and middle shelf were found for the spotted turbot, and between the middle and outer shelf for the dover sole (Table 5).
On the western coast of Baja California, four the Pleuronectidae species Pleuronichthys ritteri, P. verticalis, Lyopsetta exilis and Microstomus pacificus have been recorded. These species have previously been reported in the area by other authors (Castro-Aguirre et al., 1992; Torres-Orozco & Castro-Aguirre, 1992; Castro-Aguirre & Torres-Orozco, 1993; De la Cruz-Aguero et al., 1994; Rodriguez-Romero et al., 2011). Because they are small and difficult to catch, these flatfishes have low commercial value.
In Palos Verdes, California, these Pleuronectidae dominated the monitored demersal fish fauna in the period 1973-1993, accounting for 53-59% of the fish collected. The proportion of flatfish in the catches increased from 23 to 137 m water depths. These species accounting for the 6% of the total number of fish caught in trawls between 1973 and 1993 (Stull & Tang, 1996). Balart (1996) noted that the flatfish fishery was artisanal and multispecific, and of little relevance in Baja California, the main catches being in Vizcaino Bay. Rodriguez-Romero et al. (2008) recorded the presence of the same species of flatfish mentioned in this study on the west coast of Baja California, but they also included Parophrys vetulus and Hypsopsetta guttulata.
According to our results P. ritteri was the most abundant flatfish in the middle continental shelf, across all the study area, showing a wide range of sizes that included juveniles and adults, and with higher affinity to muddy and sandy bottoms (also recognized by Moles & Norcross, 1995). These authors mention that this species is frequent in the bycatch of the shrimp fishery, with lengths between 143 and 200 mm (within the range of sizes found in this study). Weinberg et al. (2002), recorded low abundance of spotted turbot in summer 2009 in Conception, California, between 72 and 90 m, and with bottom temperature about 7.2[degrees]C.
Further, Allen et al. (1983) reported spotted turbot off Los Angeles, California, with abundances of 6 ind [trawl.sup.-1], that were mostly juveniles.
Kramer (1991) estimated abundances of 1.2 to 16.2 ind [ha.sup.-1] for spotted turbot, mainly in shallow waters (5 to 10 m) off San Diego, California, and with a size range between 75 and 237 mm SL. Moreover, in a study conducted in San Quintin Bay, Baja California (Rosales-Casian, 1996) mentioned the presence of juveniles and adults (21-260 mm SL) of spotted turbot, in shallow waters (5-10 m), characterized by mud-sandy sediments. Both reports reflect similar results to those obtained in the present study, confirming that coastal areas with sandy sediments have high abundances of juveniles and adults of the spotted turbot. Allen (1982) considers coastal bays and lagoons as nursery areas for juvenile fish and this explanation could be valid for this species.
According to the results of this study, the highest abundance of P. verticalis was found around Vizcaino Bay, in the middle and outer continental shelves, which is dominated by sandy-muddy sediment and sand-silt (Chavez, 1995; Pedrin-Aviles & Padilla-Arredondo, 1999). On the other hand, this species have the lowest abundances in the Central region, a pattern observed also by Cross (1985) indicating a random distribution in the southern California coast.
In southern California, Allen et al. (1983) recorded low abundances of hornyhead turbot predominantly juveniles, between 10 and 65 m. Stull & Tang (1996) mentioned that this species preferred shelf depths with warm-temperate conditions and that it was more common in the mid-to-late 1980s, following El Nino. Hornyhead turbot migrated into deeper waters during the El Nino event of 1987-1988 (Allen, 2008).
Rodriguez-Romero et al. (2008) consider this species as very common in the west coast of Baja California, with sizes ranging between 81 and 256 mm SL. In San Quintin Bay, Rosales-Casian (1996) reported sizes between 60 and 140 mm. Kramer (1991), observed a range of 10 mm to 265 mm in southern California. Weinberg et al. (2002) recorded this species off Cape Mendocino (California) up to 119 m depth.
In the Gulf of California, Acevedo-Cervantes et al. (2009) recorded abundant populations of hornyhead turbot between 360 and 450 m, these depths characterized by low temperatures (7-9[degrees]C) and anoxic conditions (<0.5 mL [O.sub.2] [L.sup.-1]) into deeper waters during the El Nino event of 1987-1988 (Allen, 2008).
In the present study, captures of M. pacificus consisted mainly of juveniles inhabiting the middle shelf and outer Vizcaino Bay, dominated by sandy silt sediments with high organic matter concentrations. Hunter et al. (1990) described the ontogeny of this species in southern California in relation to the bathymetric gradient, noting that sexual maturity was reached in deep water with low dissolved oxygen levels and at a mean size of 310 mm SL.
The seasonal catch patterns may be due, in part, to changes in the bathymetric distribution of some of the flatfishes. Dover sole, for example, are more abundant on the shelf off southern California in spring and summer than in fall and winter (Cross, 1985). In northern California and Oregon, Dover sole move onto the shelf in summer to feed, and move back to the slope in winter to reproduce (Hagerman, 1952; Alton, 1972).
In the continental slope of southern California, Cross (1987) records the size range of Dover sole between 110 and 420 mm, and states that this species lives mostly in clay silt sediments with high organic matter content (5 to 14%) and cold water (6.5 to 8.2[degrees]C), these results being similar to those obtained in this study.
According to our results, specimens of Dover sole were collected with an approximate age between 1 and 3 years, ranging between 220 and 290 mm SL for males and between 280 and 350 mm for females, which would correspond to juveniles which have not reached the size of sexual maturity as estimated from maturity-length curves (Hagerman, 1952; Brodziak & Mikus, 2000; Abookire & Macewicz, 2003).
In the present study juveniles and adults of L. exilis were found in the deep stratum (90 to 200 m), with greater occurrence during the summer of 1989. This was confirmed by the results reported by Snelgrove & Haedrich (1985), for immature individuals that they found concentrated at the shallow end of the depth range while adults distribute across all depths. Rodriguez-Romero et al. (2008) consider it as a common species, with sizes ranging from 127 to 222 mm SL, and inhabiting depths between 25 and 800 m on sandy bottoms. This species is more common in cold-temperate waters, where its abundance increased beyond or below 137 m, where this species feed on nektonic benthopelagic preys such as shrimp (Stull & Tang, 1996).
Pearcy (1978) recorded the highest catches of slender sole at stations with a high percentage of clay and silt on the continental shelf off Oregon. McConnaughey & Smith (2000) concluded that the sediment texture is a crucial factor in their habitat and distribution. Furthermore, Amezcua & Nash (2001) emphasize the importance of depth and temperature gradient, and type of sediment, as important factors to explain the structure and abundance of pleuronectid species.
Water depth is one of the main factors affecting the community structure in the continental shelf and slope in coastal waters (Abookire & Norcross, 1998), and depth also plays an important role in determining the distribution of flatfish (Rogers, 1992; Gibson, 1994; Norcross et al., 1997). Benthic community structure and composition have been related to depth (Pearcy, 1978).
Between the northern and southern stations there were differences in temperature and salinity, among other parameters, such as organic matter. Other measured variables, however, such as sediment composition, in regions adjoining each sample site, may explain the additional variance in the assemblage.
The changes in the distribution of pleuronectid species between cold and warm regimes may be due in part to differences in the magnitudes of larval recruitment between these two periods and also to movements of juvenile and adult fish across different depths (Castro-Aguirre et al., 1992; Lea & Rosenblatt, 2000; Funes-Rodriguez et al., 2002; Chavez et al., 2003; Allen, 2008). Changes that occur in the oceanic environment between a cold and warm regime include increased water temperature, a deeper thermocline depth, decreased plankton productivity and reduced transport of the California Current (Hayward, 2000; Juan-Jorda et al., 2009).
On the west coast of Baja California Pleuronectidae abundance varied from 1988 to 1990. Spatial and temporal patterns are described, and inferences are made on potentially important environmental processes that influence fish assemblages. Changes in ocean conditions during the 1988-1990 periods affected the occurrence and abundance of fish in the west coast of Baja California (Castro-Aguirre et al., 1992).
The conclusions of this study indicate that the distribution of Pleuronectidae species varies with depth across the shelf during different oceanic regime periods.
The sex ratio found for these species in the present work was close to 1:1, which is the usual value found for Pleuronectidae (Kramer, 1991; Minami & Tanaka, 1992; Martinez-Munoz & Ortega-Salas, 1999, 2001, 2010).
Length-weight relationship analysis of males, females, and undetermined, shows allometric growth and differences, in the relative growth rate, between sexes of P. ritteri and P. verticalis. Such allometric growth shows similar characteristics (positive allometric growth) to those found by Hagerman (1952) and Martinez-Munoz & Ortega-Salas (1999, 2001) in California and other regions.
We have found obvious differences between sexes for the length-weight relationships of spotted turbot and hornyhead turbot. Cooper (1994) estimated the length to weight ratio for hornyhead turbot in southern California and found, differences between the sexes; the values of the power coefficients of the equation were lower.
We present some estimates of the parameters of the weight-length relationship of species of flatfish along the US west coast in the Table 6. We have found a well-pronounced size sexual dimorphism between male and female turbot. Female were considerably larger than males, which probably relates to earlier maturation, greater longevity, and lower growth rates of females. As a result, this leads to a dominance of females among the oldest fishes that is also characteristic of many other flatfish species (Chen et al., 1992).
Jacobson & Hunter (1993), in their analysis of bathymetric patterns in population structure, also found that Dover sole segregated by sex. The authors attribute such differences to the fact that large Dover sole males undertake seasonal movements less frequently than females, and therefore their growth rates may be expected to be less heterogeneous than those of females that move from the continental slope to the more productive waters of continental shelf during spring.
The length-weight relationship may be influenced by sex, maturity, geographical location, and environmental condition (Bagenal & Tesch, 1978; Weatherly & Gill, 1987; Wootton, 1990; Murphy et al., 1991).
This study was partially supported by the Consejo Nacional de Ciencia y Tecnologia de Mexico (CONACYT), grant P22OCC0R880518, and Universidad Nacional Autonoma de Mexico, which provided the B/O "El Puma" from 1988 to 1991. We also thanks the Instituto de Ciencias del Mar y Limnologia (UNAM) for allowing us to analyze the information, the Centro de Investigaciones Biologicas del Noroeste for processing the surface sediment, to S. Pedrin and G. Padilla for their technical support.
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Received: 13 November 2012; Accepted: 12 September 2013
Marco A. Martinez-Munoz (1), Felipe Fernandez (2), Francisco Arreguin-Sanchez (3), Joandomenec Ros (2) Ricardo Ramirez-Murillo (4), Marco Antonio Solis-Benites (5) & Domenec Lloris (6)
(1) Departamento de Formacion Basica, Unidad Profesional Interdisciplinaria de Ingenieria y Ciencias Sociales y Administrativas, IPN, Av. Te No. 950 Col. Granjas Mexico, 08400, Mexico D.F., Mexico
(2) Departament d'Ecologia, Facultat de Biologia, Universitat de Barcelona Diagonal 645, 08028 Barcelona, Spain
(3) Centro Interdisciplinario de Ciencias Marinas, Instituto Politecnico Nacional Apdo. Postal 592, 23090 La Paz, Baja California Sur, Mexico
(4) Instituto de Educacion Media Superior del DF (IEMS-DF), Plantel Tlalpan I Av. San Lorenzo No. 290, Col. del Valle Sur 03100, Mexico D.F., Mexico
(5) Grupo DePSEA Instituto Antonio Raimondi, Laboratorio de Ecologia Marina Facultad de Ciencias Biologicas, Universidad Nacional Mayor de San Marcos, Apartado 1898, Lima, Peru
(6) Institut de Ciencies del Mar (CMIMA-CSIC), Pasage Maritim de la Barceloneta 37-49
Corresponding author: Marco A. Martinez-Munoz (email@example.com)
Table 1. Cruises (month, year), season (Spr = spring; Sum = summer), number of trawls with Pleuronectidae (trawl-sp), depth range (m), surface temperature (ST), bottom temperature (BT), salinity (psu), type of sediment (%), abundance (Abun), biomass (Biom), during the study period 1988-1990, off the western coast of Baja California. Cruises Season Total No. Depth Temperature Month/Year trawl trawl/sp (m) ([degrees]C) ST Apr-Jul-1988 Spr-Sum 16 11 13-56 -- Oct-1988 Fall 16 4 31-180 21.2-28.0 Feb-1989 Winter 17 3 25-168 16.0-28.0 Jul-1989 Summer 19 17 31-197 13.5-24.0 Mar-1990 Winter 18 15 37-237 13.8-19.0 Sep-1990 Summer 19 16 42-312 16.0-32.0 Cruises Salinity Sediment (%) Month/Year BT (psu) Sand Silt Clay Apr-Jul-1988 -- -- 78.3 12.1 9.7 Oct-1988 14.0-19.2 28.0-34.2 79 13.3 7.6 Feb-1989 12.5-15.1 30.2-35.0 70.6 20.7 8.9 Jul-1989 11.0-22.0 31.0-34.5 64.5 25.1 10.6 Mar-1990 11.0-18.0 30.5-34.6 65.2 23.3 11.6 Sep-1990 11.5-24.6 33.5-39.2 57.2 28.0 15.1 Cruises Abun Biom Month/Year (ind (kg [ha.sup.-1]) [ha.sup.-1]) Apr-Jul-1988 745 49.2 Oct-1988 32 3.1 Feb-1989 31 1.0 Jul-1989 2013 61.0 Mar-1990 193 13.5 Sep-1990 152 16.0 Table 2. Means (standard deviation) of environmental variables and comparison among years in the three regions and strata of the continental shelf off the western coast of Baja California. Surface temperature (Surf. T.), bottom temperature (Bott. T.), salinity, and organic matter (O. Mat). Southern 1,988 1,989 1,990 Surf. T. 24.1 (1.9) 17.7 (1.2) 20.9 (4.4) Bott. T. 13.7 (0.7) 14.1 (1.0) 15.3 (3.2) Salinity 31.7 (2.0) 31.7 (0.3) 35.3 (1.9) O. Mat. 0.67 (0.2) 0.3 (0.2) 0.91 (0.3) Region Center 1,988 1,989 1,990 Surf. T. 22.6 (0.7) 19.2 (3.6) 23.1 (5.1) Bott. T. 16.9 (1.4) 14.6 (2.1) 14.5 (3.0) Salinity 31.9 (0.3) 32.1 (1.0) 34.4 (0.2) O. Mat. 1.14 (0.3) 1.30 (0.6) 2.1 (1.1) Northern 1,988 1,989 1,990 Surf. T. -- 17.1 (1.4) 19.9 (3.3) Bott. T. -- 12.2 (2.0) 13.3 (2.2) Salinity -- 33.1 (0.1) 33.7 (0.1) O. Mat. -- 1.9 (0.7) 1.86 (0.4) Inner 1,988 1,989 1,990 Surf. T. 23.1 (00.2) 18.5 (2.6) 21.0 (4.3) Bott. T. 18.8 (0.4) 15.9 (2.7) 16.3 (3.1) Salinity 31.6 (0.2) 32.2 (0.5) 34.0 (0.4) O. Mat. 0.8 (0.0) 1.0 (0.2) 1.3 (0.3) Shelf Middle 1,988 1,989 1,990 Surf. T. 22.9 (0.7) 18.3 (3.2) 22.2 (4.6) Bott. T. 16.0 (1.0) 13.5 (1.9) 15.5 (3.3) Salinity 32.2 (1.0) 32.1 (1.2) 34.1 (0.4) O. Mat. 1.0 (0.3) 1.5 (0.7) 1.6 (0.7) Outer 1,988 1,989 1,990 Surf. T. 23.9 (2.4) 17.6 (1.2) 21.2 (4.9) Bott. T. 15.2 (0.9) 12.9 (1.1) 13.0 (1.7) Salinity 31.4 (1.8) 31.8 (0.3) 34.8 (1.4) O. Mat. 0.91 (0.3) 1.1 (0.8) 1.8 (1.2) Table 3. Summary of the ordenation axes and intra-set correlation of environmental variables with the first two axis of redundancy analysis (RDA) in the western coast of Baja California (1988-1990). Axes Summary of ordenation axes 1 2 Eigenvalues 0.171 0.032 Species-environment correlations 0.482 0.404 Cumulative percentage variance Of species data 17.1 20.3 Of species-environment relation 80.4 95.3 Sum of all canonical eigenvalues 0.213 Sum of all eigenvalues 1.000 Correlation of environmental variables Northern -0.4606 0.1452 Inner shelf 0.7546 -0.0235 Outer shelf -0.4654 0.1167 Surface temperature -0.6543 -0.4695 Bottom temperature -0.5792 -0.5321 Salinity -0.4084 -0.5989 Organic matter -0.3510 0.0052 Silt -0.4472 0.1255 Sand 0.3972 0.0511 Table 4. Summary of the parameters of the weight-length relationship and sex ratio of the species of Pleuronectidae off the western coast of Baja California. * Statistical difference at P = 0.05. Species n A b Pleuronichthys ritteri [female] 133 3.24*([10.sup.-6]) 3.3718 [male] 185 2.83*([10.sup.-6]) 3.4231 All 422 3.97*([10.sup.-6]) 3.3443 Pleuronichthys verticalis [female] 20 4.38*([10.sup.-6]) 3.3597 [male] 14 1.13*([10.sup.-5]) 3.1561 All 47 4.59*([10.sup.-6]) 3.3474 Lyopsetta exilis [female] 43 2.87*([10.sup.-5]) 2.8576 [male] 32 1.06*([10.sup.-5]) 3.0858 All 99 2.28*([10.sup.-6]) 3.3808 Microstomus pacificus [female] 17 3.08*([10.sup.-5]) 2.8120 [male] 10 2.18*(10-7) 3.7887 All 27 1.29*([10.sup.-5]) 2.9748 Species [r.sup.2] Ratio sex Pleuronichthys ritteri [female] 0.97 [male] 0.94 All 0.96 1:1.4 * Pleuronichthys verticalis [female] 0.97 [male] 0.95 All 0.97 1:0.7 Lyopsetta exilis [female] 0.80 [male] 0.65 All 0.89 1:0.8 Microstomus pacificus [female] 0.93 [male] 0.92 All 0.88 1:0.7 Table 5. Comparison of slopes between sexes, years, region, and shelf areas of the species of Pleuronectidae off the western coast of Baja California. 1988-1990. *Statistical difference at P = 0.05. Species n F t [r.sup.2] P = 0.05 Pleuronichthys ritteri Sexes 318 1716.84 2.619 0.92 * 88-89 358 820.19 0.099 0.87 0.920 88-90 166 526.8 1.952 0.91 * 89-90 212 450.9 0.990 0.86 0.323 Region South-Center 258 629.54 1.927 0.88 * Center-North 246 634.80 6.149 0.88 * South-North 234 627.92 6.500 0.89 * Shelf Inner-Middle 269 576.11 1.954 0.86 * Inner-Outer 340 886.47 0.561 0.88 0.574 Middle-Outer 129 307.35 1.643 0.88 0.103 Pleuronichthys verticalis Sexes 34 309.34 4.124 0.97 * 89-90 47 237.61 1.270 0.94 0.2107 Region Centre-North 47 286.32 2.254 0.95 * Shelf Inner-Middle 40 184.36 1.241 0.93 0.2226 Inner-Outer 21 108.61 0.692 0.95 0.4978 Middle-Outer 33 160.65 0.037 0.94 0.9706 Lyopsetta exilis Sexes 75 104.94 0.8544 0.82 0.3958 Middle-Outer 99 124.91 1.591 0.79 0.1147 Microstomus pacificus Sexes 27 56.12 0.5330 0.88 0.5991 Middle-Outer 27 103.52 3.767 0.93 * Table 6. Estimated parameters of the weight-length relationship of some Pleuronectidae species along the US West coast. Species a b Microstomus pacificus All 4.0659 x [10.sup.-3] 3.2479 Male 3.7064 x [10.sup.-3] 3.2736 Female 4.4149 x [10.sup.-3] 3.2254 Male 2.440 x [10.sup.-3] 2.95 Female 2.389 x [10.sup.-3] 2.97 Pleuronichthys verticalis Male 0.8915 1.767 Female 0.3027 2.145 Hypsopsetta guttulata All 2.213 x [10.sup.-5] 3.044 Glyptocephalus zachirus All 8.647 x [10.sup.-4] 3.5553 Male 1.026 x [10.sup.-3] 3.5598 Female 8.158 x [10.sup.-4] 3.5112 Species Locality Microstomus pacificus All Pacific northwestern Male US West coast Female Male Eureka US West coast Female Pleuronichthys verticalis Male Southern California Female US West coast Hypsopsetta guttulata All Anaheim, California US West coast Glyptocephalus zachirus All Oregon, US West coast Male Female Species Source Microstomus pacificus All Brodziak & Mikus (2000) Male Female Male Hagerman (1952) Female Pleuronichthys verticalis Male Cooper (1994) Female Hypsopsetta guttulata All Lane (1975) Glyptocephalus zachirus All Hosie & Horton (1977) Male Female
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|Title Annotation:||articulo en ingles|
|Author:||Martinez-Munoz, Marco A.; Fernandez, Felipe; Arreguin-Sanchez, Francisco; Ros, Joandomenec; Ramirez-|
|Publication:||Latin American Journal of Aquatic Research|
|Date:||Nov 1, 2013|
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