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Composicion de especies, estructura de tallas e indices reproductivos de pez espada (Xiphias gladius) en la zona de isla de Pascua.

Species catch composition, length structure and reproductive indices of swordfish (Xiphias gladius) at Easter Island zone

INTRODUCTION

The early Chilean swordfish fishery (1930-1985) consisted of an artisanal harpoon fleet that operated mainly off the country's northern and central coasts (Barbieri et al., 1990). The following years saw the introduction of gillnets and the use of larger, more automated vessels, which permitted fishing between 27[degrees] and 40[degrees]S within the Economic Exclusive Zone (EEZ). According to Barbieri et al. (1998), as of 1989, artisanal landings decreased in conjunction with the rising importance of the industrial fleet, which has longer vessels and mechanized operating systems for fishing and freezing the catches. This fleet relies on surface longlines; these are lines with hooks and live bait that are suspended from the surface and can reach up to 70 km in length (Barbieri et al., 1998; Ward et al., 2000; Yanez et al., 2003).

The swordfish harpoon fishery was largely seasonal and the fishing season off northern and central Chile lasted only a few months. However, the implementation of gillnets and the use of satellite sea surface temperature images for seeking out fishing zones prolonged the fishing season through September-October of each year. Likewise, the industrial longline fleet, whose fishing trips last up to two months, extended the fishing season until November and December and expanded the fishing zone beyond the EEZ, reaching up to 800 nm from the coast (Barbieri et al., 1998). At present, the industrial fleet halts activities in summer due to low yields in the traditional fishing zones off the Chilean coast. Nonetheless, the coinciding interests of private businesses and government in some research projects have encouraged some companies with freezer vessels to explore the oceanic area around Isla de Pascua (Easter Island) in late spring and summer in search of new fishing zones and yields that would allow these vessels to operate year-round.

Regarding other oceanic areas with active swordfish fisheries (Ovchinnikov, 1970; Beckett, 1974; Palko et al., 1981; De Metrio et al., 1989; Ward & Elscot, 2000), very little is known about the swordfish fishery in the southeastern Pacific in terms of both the species present and vulnerable to the fishing gear as well as their relative abundances and biological parameters. With the exception of the works done using information from the Japanese tuna fleet (Shingu et al., 1974; Miyabe & Bayliff, 1987; Nishikawa & Shimizu, 1991; Uosaki & Bayliff, 1999; Okamoto & Bayliff, 2003), or evaluation studies done mainly by multinational organisms (Bartoo & Coan, 1989; Joseph et al., 1994; Hinton & Deriso, 1998; Hinton & Bayliff, 2002; Hinton et al., 2005), no background information is available on the swordfish fishery in the open ocean off Chile. A study done by Zarate (1997) identified a possible swordfish reproduction zone in the southeastern Pacific in the area surrounding Isla de Pascua Nonetheless, as this area is not usually visited by commercial Chilean vessels, the species catch composition, population structure, and reproductive information required to validate the hypothesis of swordfish reproduction in this area are not known.

For the conservation of highly migratory species exploited in international waters, it is important to have updated biological-fishery information for managing fisheries such as that of swordfish. Therefore, the objectives of the present study were to characterize the catches and yields of longline swordfish vessels and the reproductive aspects of the target species, in the waters surrounding Isla de Pascua and Isla Salas y Gomez, where exploratory campaigns were carried out between 2001 and 2006.

MATERIALS AND METHODS

The study area included the fishing zone of the EEZ and the high seas adjacent to Isla de Pascua and Isla Salas y Gomez (15[degrees]-35[degrees]S; 90[degrees]-120[degrees]W). This area was prospected during five summertime campaigns from 2001 to 2005-2006 (Fig. 1). Each fishing campaign was carried out by an industrial longline freezer vessel (Table 1). American-type surface longlines (Florida style) were used; these are horizontal longlines in which a mother line (polyamide monofilament) is suspended by buoys at the surface; 5 monofilament gangions with 60-75 g swivel and balanced Mustad-type hooks (9/0) are placed at regular intervals (40-50 m) between each buoy. Squid (Illex argentinus) was the main bait used, along with chemical lights (lightsticks) for visual attraction. Information on the operational regime was recorded for each set, that is, the position and time of setting and retrieval, and the number of hooks used. In the 2002 and 2004 campaigns, the effective catch depth (m) and temperature ([degrees]C) were recorded using MICREL P2T600 sensors that were configured to record the variables every 30 s throughout the entire fishing period.

[FIGURE 1 OMITTED]

All the ichthyofauna caught was identified to the species level using FAO keys and manuals (Collette & Nauen, 1983; Compagno, 1984a, 1984b; Nakamura, 1985) and were then recorded (census sampling). The eviscerated weight of the species of commercial interest was determined on industrial scales or, in their absence, with conversion tables based on the length of the specimen. In order to determine the relative importance of the target species and bycatch, we calculated the nominal yield in number of individuals and eviscerated weight (kg) for every 1,000 hooks set (ind or kg 1,000 [hook.sup.-1]). In order to compare the nominal swordfish yield between each of the campaigns carried out (years), a one-way analysis of variance was performed (ANOVA).

For swordfish and marlins, the length was measured (rounded to the lowest centimeter) from the lower jaw to the fork of the caudal fin (LJFL), whereas for tuna and teleost fishes, the fork length (FL) was recorded. In the case of the sharks, the length was measured from the nose to the fork of the caudal fin (FL). Histograms of frequency were obtained for the target species and most frequent bycatch species ([greater than or equal to] 4% in number). One-way ANOVA was used to compare the average sizes of both swordfish and blue sharks per campaign and sex. For swordfish, the sex was determined through macroscopic observation of the gonads, whereas in the elasmobranchs, it was established by the presence of gonopods. The sex ratio of the swordfish was determined as the percentage of females with respect to the total sexed specimens. The female gonads were weighed in situ using a scale with precision to the gram; for specimens over the size of first sexual maturity (165 cm LJFL; Zarate, 1997), the gonadic index (GI) was calculated using the following expression, modified from Kume & Joseph (1969):

IG = (w/[LMIH.sup.3]) x [10.sup.4]

where w corresponds to the weight of the gonad (g) and LJFL to the lower jaw-fork length (cm). The calculations were done for each specimen, with stratified results per year and month.

RESULTS

Spatially, the fishing activities of the five campaigns covered the entire study area, with certain clusters of sets to the east and northwest of Isla de Pascua (Fig. 1). A total of 150 fishing sets were completed, in which 155,060 hooks were set. The number of hooks per set ranged from 320 to 1,800, with an average (standard deviation; SD) of 1,033.7 (SD = 323.6). Information registered by sensors during 44 fishing sets (29%) indicated that the effective catch depth oscillated between 34.2 and 176.8 m (average = 54.7 m; SD = 21.8), and an average water temperature of 21.8[degrees]C (SD = 1.8[degrees]C) in a range of 15.8 to 25.4[degrees]C.

In total, 3,781 fish were caught: 1,667 (44.1%) were swordfish, 1,071 (28.3%) sharks, 456 (12.1%) marlins, 318 (8.4%) tuna, and 269 (7.1%) other teleosts. Of the sharks, the most important species was the blue shark (Prionace glauca) (n = 622; 16.5% of the total catch), followed by the brown sharks (Carcharhinus spp.) (n = 262; 6.9%). Among the elasmobranchs, the observers also identified the pelagic stingray (Pteroplatytrygon violacea) and the cookie-cutter shark (Isistius brasiliensis). These individuals were immediately discarded and, thus, it was not possible to include them in the totals. Of the tunas and istiophorids, the striped marlin (Tetrapturus audax) (n = 301; 8.0%) and the yellowfin tuna (Thunnus albacares) (n = 185; 4.9%) were the most important species. Table 2 shows the species catch composition and nominal catch rates in number and weight.

The nominal fishing yield for all species reached 964.1 kg x 1,000 [hook.sup.-1] (24.4 ind x 1,000 [hook.sup.-1]), with the swordfish having the greatest total yield (587.9 kg 1,000 [hook.sup.-1]; 10.8 ind x 1,000 [hook.sup.-1]), followed by the blue shark (106.4 kg x 1,000 [hook.sup.-1]; 4.0 ind x 1,000 [hook.sup.-1]), and the striped marlin (64.6 kg x 1,000 [hook.sup.-1]; 1.9 ind x 1,000 [hook.sup.-1]) (Table 2). No significant differences were observed in the 2001 to 2003 swordfish yields (ANOVA, [F.sub.2,63] = 1.55; p = 0.22). On the other hand, during the 2004 and 2005-2006 campaigns, although the yields were very similar, they differed from the results obtained in previous years, probably due to the experience accumulated in the previous campaigns.

The total number of specimens measured in all the campaigns reached 3,528, with swordfish constituting 1,816 (51.5%). The swordfish catches were mostly male, with a global sex ratio of 40.1% females. The sex ratio at size (Fig. 2) indicated a predominance of males to 255 cm LJFL; from this size on, females predominated. No differences were observed in the average sizes of swordfish by sex (ANOVA, [F.sub.1,1.744] = 1.99; p = 0.16). This tendency was maintained in all seasons except for the campaign done between December 2005 and February 2006, in which the average size was greater for the females (ANOVA, [F.sub.1,464] = 9.91; p < 0.01). When the average sizes were grouped by sex and compared annually, significant differences were found (ANOVA, [F.sub.4,1.741] = 10.35; p < 0.01), with catches of larger specimens mostly in 2005-2006. The range of grouped sizes fluctuated between 75 and 325 cm LJFL, with an average of 170.2 cm (SD = 38.5) (Table 3). The size structure (Fig. 3a) was relatively symmetrical and multimodal, with the principle modes centered on 150 and 175 cm LJFL in males (Fig. 3b) and 145 and 165 cm in females (Fig. 3c). Male blue sharks were predominant in most seasons, with a global sexual proportion of 43.1% of females. Differences were observed in the average sizes between sexes (ANOVA, [F.sub.1,559] = 221.06; p < 0.001), with averages 223.1 cm FL (males) and 186.0 cm FL (females). For males, the FL varied between 115 and 278 cm (n = 319) and for females between 105 and 275 cm (n = 242). The size frequency histogram (Fig. 3d) showed three main modes: mostly females at 175 cm (Fig. 3f) and mostly males at 210 and 260 cm (Fig. 3e). It should be pointed out that females showed exclusive predominance up to 195 cm, after which the males predominated. For striped marlin, the average LJFL was 215.0 cm (SD = 24.5; n = 227), ranging from 119 to 319 cm. A leptokurtic frequency distribution was observed, with a mode centered on 210 cm LJFL (Fig. 4a). The average size of the brown sharks was 182.6 cm FL (SD = 30.0; n = 140) with a somewhat symmetrical and multimodal frequency distribution; the principle mode was 170 cm FL (Fig. 4b). The sexual proportions did not differ, with 49.6% (n = 139) being female. The yellowfin tuna averaged 119.8 cm FL (SD = 27.5, n = 191), ranging in size from 65 to 167 cm, with the principle mode of the size frequency distribution centered on 140 cm FL (Fig. 4c). The last highly represented species in the catches was the shortfin mako shark (Isurus oxyrinchus), which presented an average FL of 210.4 cm (SD = 34.1; n = 166), and a size structure with principle modes at 160 and 230 cm FL (Fig. 4d). As with P. glauca, the sexual proportion favored males, with 30.9% females (n = 152).

[FIGURE 2 OMITTED]

A total of 670 females were sampled for a reproductive analysis of the swordfish. Of these, 343 corresponded to specimens longer than the size at first sexual maturity. The maximum GI values were over 7 in all the campaigns, although the indicators of centrality for the annual GI (medians) were not very high (0.61.7) (Fig. 5a). On a monthly scale (Fig. 5b), the behavior of the indicator was similar, with the medians ranging between 0.6 in November (n = 72) and 2.7 in March (n = 5). The greatest individual observations of GI were concentrated from December to February and then declined in March (Fig. 5b).

DISCUSSION

Relatively few publications on longline pelagic fisheries have covered the species catch composition. In the five fishing campaigns studied herein, 23 fish species were caught, of which 17 are considered to be commercial and six incidental. These latter bycatch species were immediately discarded and included the pelagic stingray, the cookie-cutter shark, "barracudas" (Gempilus sp. and Alepisaurus sp.), an amberjack (Seriola sp.), and the skipjack tuna (Katsuwonus pelamis). Barria et al. (2005) reported the presence of 35 species caught by the Chilean surface longline fishing fleet in 2004 in the traditional fishing zones: 22 teleost fishes, 9 cartilaginous fishes, and 6 species from other groups such as cephalopods, mammals, birds, and turtles. The results presented herein show a lower number of species in the oceanic zone off Chile than in the more coastal zone. Nonetheless, these results must be considered carefully since the oceanic fishing effort was significantly lower than that in the common fishing zones. Moreover, it is also possible that the vulnerability of some species could change due to different conditions of the physical environment. In the swordfish fishery of the Atlantic Ocean (Uruguayan EEZ and international waters), 50 species have been recorded: 27 teleost fishes, 15 cartilaginous fishes, and eight other species of birds, mammals, and turtles (Marin et al., 1998). On the other hand, landings of the Spanish longline swordfish fishery, as reported by Buencuerpo et al. (1998), included 25 species, the most common being the shortfin mako shark, the blue shark, and swordfish.

[FIGURE 3 OMITTED]

The analysis per species indicated that swordfish made up approximately 45% of the total catches in number; the sharks (mostly blue shark), marlins, and tuna, respectively constituted 28%, 12%, and 8%. The most important species in the bycatch of the swordfish fishery carried out in the traditional fishing zones of the Chilean fleet were the blue shark (57.5%) and the shortfin mako shark (18.1%) (Barria et al., 2005). The numerical dominance observed for swordfish in this study agrees with that reported by Beerkircher et al. (2002) for the pelagic longline fishery on the southeastern coast of the United States (22[degrees]-35[degrees]N, 71[degrees]82[degrees]W). In that area, swordfish made up 40% of the catches, whereas elasmobranchs, tuna, and marlins were respectively 15%, 13%, and 4%. The shark Carcharhinus falciformis was the dominant elasmobranch species (31.4%). On the contrary, Buencuerpo et al. (1998) reported a greater proportion of sharks in the catches from the Strait of Gibraltar in the East Atlantic. There, the most common species were the blue shark (67%), swordfish (17%), and shortfin mako shark (12%). Kotas et al. (2000) reported catches off South Brazil that were 69% sharks and 31% teleosts. Of these sharks, the blue shark represented 50% the total catch, whereas swordfish were only 14% of the bony fishes.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

The difference in the proportion of teleost fishes (principally swordfish) and elasmobranchs could be due in part to the longline design. For example, the North American fleet uses monofilament (polyamide) leaders, whereas the Spanish fleet uses wire. This probably has an important effect on the retention of sharks and the species catch composition (Berkeley et al., 1981; Marin et al., 1998; Kotas et al. 2000). Recently, Kerstetter & Graves (2006), working in the North Atlantic, also found differences in the catch compositions depending on the type of hook used and the season of the year. With a circular-type hook, records showed 35% elasmobranchs (principally pelagic stingrays and blue sharks), followed by tuna (24%), other teleost fishes (19%), and swordfish (17%). When "J" type hooks were used, however, the greatest catches corresponded to swordfish (65%), followed by teleost fishes (19%), principally Lepidocybium flavobrunneum, and sharks and rays (10%). Another source of variability in the composition of the long-line catches corresponds to the fishery target species. Lins et al. (2005) studied the catches of both local and foreign longline fleets off north-eastern Brazil, finding that the catches consisted mainly of bigeye tuna (39%), yellowfin tuna (36%), and swordfish (23%). These results denote the strong intentions of the foreign fleets (oriental) to catch tuna rather than swordfish. Thus, both the constitution of the gear and the spatial-temporal variability can produce significant differences in the composition and number of species in the catches. Future studies are needed around Isla de Pascua to evaluate the presence and relative abundance of the fish populations that inhabit this region in other seasons of the year.

In the study area, global swordfish yields were greater (587.9 kg or 10.8 ind x 1,000 [hook.sup.-1]) than the value recorded by the Chilean industrial fleet in 2005 (497 kg x 1,000 [hook.sup.-1]) (Barria et al., 2006). Nonetheless, given the results of the monthly fleet operation--a minimum yield in December (309 kg x 1,000 [hook.sup.-1]) and a maximum in November (729 kg x 1,000 [hook.sup.-1])--the yield in this area is intermediate. In the North Atlantic, Stone & Dixon (2001) reported an average of 38.8 ind ~1,440 [hook.sup.-1], whereas Kerstetter & Graves (2006) and Marin et al. (1998) found catch rates of 9.0 to 33.7 ind x 1,000 [hook.sup.-1] and 0.7 to 8.7 ind x 1000 [hook.sup.-1], respectively.

When using the sizes of first sexual maturity estimated by Zarate (1997), the catches off Isla de Pascua consisted of juvenile and adult swordfish specimens, with similar size structures and principle modes for both sexes. The swordfish population structure was dominated by males, with a total sexual proportion of 40.1% females. The analysis of the sexual proportion by size range indicated that the percentage of males is predominant in sizes smaller than 240 cm LJFL, after which the female proportion is predominant. Similar results have been found by Guitart-Manday (1964 fide Taylor & Murphy, 1992), Mejuto et al. (1995) and Arocha & Lee (1996). It has been established that swordfish over 220 to 230 cm are generally females, since the males have a lower growth rate and a shorter life span (Suzuki & Miyabe, 1990; Taylor & Murphy, 1992). The difference in the sexual proportion was also explained by a change in behavior in the spawning period as a result of a change in the catchability or availability of the mature females (De Martini et al., 2000). Since the present work only includes observations from spring and summer, it was not possible to determine seasonal changes in the sexual proportion. Nevertheless, unlike that reported by Barria et al. (2005) for the traditional fishing zones close to the continent, where the monthly sexual proportion is around 50% (or slightly greater) for females, these results suggest a sexual segregation, probably associated with a reproductive zone of this species (Taylor & Murphy, 1992; Arocha & Lee, 1996; De Martini et al., 2000).

From a macroscopic point of view, swordfish reproduction in the Eastern Pacific has been studied by diverse authors (Kume & Joseph, 1969; Uchiyama & Shomura, 1974; Weber & Goldberg, 1986; Miyabe & Bayliff, 1987; Nakano & Bayliff, 1992; Garcia-Cortes & Mejuto, 2002). Nonetheless, the criteria for calculating reproductive indexes vary between authors, who use different measures of length (e.g. LJFL vs. eye-fork length, EFL) and different sizes at first sexual maturity for the fish. For example, Kume & Joseph (1969) consider females to be mature when they have gonad indexes [greater than or equal to] 3 using the EFL, or [greater than or equal to] 2.09 when using the LJFL, according to the transformation of Mejuto & Garcia-Cortes (2003). Other authors such as Arocha et al. (1994) and Macias et al. (2005), who studied swordfish reproduction in the Atlantic and Mediterranean, respectively, qualify specimens as mature with a GI [greater than or equal to] 3. However, the average value of this indicator is used for both groups (size, spatial, or seasonal) and individual specimens. In general, these indexes should be used with care if they are not complemented with a histological analysis (DeVlaming et al., 1982).

According to this information, the results obtained in the present study indicate specimens with advanced states of gonad development in the five fishing campaigns. This confirms the report by Zarate (1997) for 1992 to 1993; this author used histology to identify fishes with a high degree of sexual maturity, probably about to spawning, between November and December around Isla de Pascua. The results presented herein show that this zone is a recurrent area for swordfish reproduction in the southeastern Pacific. Nonetheless, and as reported by Zarate (1997), our study revealed relatively few females in reproductive conditions; this justifies maintaining a reproductive monitoring program in this area for several seasons.

The blue shark presented a higher proportion of males. Spatially and seasonally, the segregation of pelagic sharks by sex and size has been documented by Nakano (1994) in the Pacific. Hazin et al. (1994) indicated that females might segregate away from males towards shallower and warmer waters to facilitate the reproductive process. The size structure between sexes also showed differences in its composition, with a significant male predominance over 220 cm FL. Thus, considering the size of first maturity for females and males (Pratt, 1979), the catches were principally made up of adult males and a lesser proportion of adult females. Differentiated growth was also observed in which the females attained a larger size. This characteristic is rather widespread within the elasmobranchs and is attributed to a reproductive strategy, since the females need to be larger in size in order to maintain their offspring. Previous studies have indicated that the blue shark is one of the most productive and abundant species among the pelagic sharks (Cortes, 2000; Campana et al., 2005). The results presented show that, although it is an important species within the catches, its yield is relatively low (4.0 ind x 1,000 [hook.sup.-1]) in this area and period. The catch rates for the blue shark in the North Atlantic seem to be greater. For example, Campana et al. (2005), through a literature review, estimated an average catch rate of 18.4 ind x 1,000 [hook.sup.-1]. Nonetheless, the variability in the Atlantic is high, with catch rates between 5.1 and 40 ind x 1,000 [hook.sup.-1]. On the other hand, off South Brazil, Kotas et al. (2000) observed catches of 3.4 to 40.6 ind x 1,000 [hook.sup.-1]. In the waters off New Zealand, Francis et al. (2001) recorded large interannual variability between fleets and regions, with average values of 1.15 to 114 ind x 1,000 [hook.sup.-1] and typical values of 15 ind x 1,000 [hook.sup.-1]. In Australian waters, the average catch was 5.5 ind x 1,000 [hook.sup.-1], but occasionally reached 100 specimens (Stevens, 1992).

The short-fin mako shark presented an elevated yield in weight (60.0 kg x 1,000 [hook.sup.-1]). Although the catch rate was low, these individuals presented a considerable average eviscerated weight. This species seems to be more abundant in the Atlantic, where in some areas it reaches more than 10% of the catches (Buencuerpo et al., 1998). In the North American longline fleet of the Caribbean and the Gulf of Mexico in the Atlantic, the catch indexes reported by Cramer (1996) oscillated between 3.52 and 11.86 (ind x 1,000 [hook.sup.-1]) from 1985 to 1996. However, recent studies in the eastern North Atlantic, with information from longline vessels that operated between 1992 and 2003, report values between 0.1 and 1.1 ind x 1,000 [hook.sup.-1] (Beerkircher, 2005).

In general, factors such as the intensity of the fishing effort and the longline design could influence the catches of this type of fishery. Information on tuna and istiophorid yields is scarce. Stone & Dixon, (2001) report yields of 6.0 ind x 1.440 [hook.sup.-1] for Tetrapturus albidus and 1.0 ind x 1,440 [hook.sup.-1] for the yellowfin tuna, whereas Kerstetter & Graves (2006) report a catch rate between 6.4 and 10.7 ind x 1.440 [hook.sup.-1] for the yellowfin tuna, but note that this is highly influenced by the season and type of hook used. In the future, it will be necessary to perform studies aimed at researching the trend in the catch rates of the target species, as well as in the bycatch, given the increasing effort of diverse fleets in this area. On the other hand, special emphasis is given the identification and quantification of the species found in this zone, especially for the bycatch, since this information will be fundamental at the moment of evaluating the real impact of fishing on the community structure.

ACKNOWLEDGEMENTS

The authors give special thanks to the officers and crews of the vessels Tami S (Pesquera Omega) and Talcan (Pesquera del Estrecho) for their good disposition and help with the tasks carried out on-board. We also thank R. Lorca, J. Azocar, J.M. Madrid, M. Leiva and M. Cortes for their assistance and collaboration in sampling. Finally we appreciate the contributions from anonymous reviewers that improved the manuscript.

Received: 20 November 2006; Accepted: 24 Jun 2008

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Rodrigo Vega (1), Roberto Licandeo (2), Gaston Rosson (3) & Eleuterio Yanez (4)

(1) Universidad Austral de Chile, Instituto de Ecologia y Evolucion, Casilla 567, Valdivia, Chile

(2) Departamento de Oceanografia, Universidad de Concepcion, Concepcion, Chile

(3) Instituto de Fomento Pesquero, Departamento de Evaluacion de Pesquerias, Valparaiso, Chile

(4) Pontificia Universidad Catolica de Valparaiso, Casilla 1020, Valparaiso, Chile

Autor corresponsal: Rodrigo Vega (rodrigovega@uach.cl)
Table 1. Period prospecting, effort and total catch for each cruise to
the area of Easter Island.

Tabla 1. Periodo de prospeccion, esfuerzo desplegado y captura total
obtenida en cada campana a la zona de isla de Pascua. Cruise (year)

                              2001      2002      2003

Season                       Jan-Mar   Jan-Feb   Jan-Feb

Effort        No sets          22        20        24
              No hooks       30,910    24,481    29,193
Total catch   No specimens     428       524       536
              Weight (kg)    19,168    19,018    19,635

                              2004     2005-2006

Season                       Oct-Dec    Dec-Feb

Effort        No sets          38         46
              No hooks       31,710     38,766
Total catch   No specimens     951       1342
              Weight (kg)    36,175     55,503

Table 2. Catch, nominal yield and average eviscerated weight of the
species retained during the fishing trips to the study zone.

Tabla 2. Captura, rendimiento nominal y peso eviscerado promedio de
las especies retenidas durante los viajes de pesca a la zona de
estudio.

                                                       Catch

Common name           Scientific name              Number    (%)

Swordfish             Xiphias gladius               1,667   44.1
Blue shark            Prionace glauca                 622   16.5
Striped marlin        Tetrapturus audax               301    8.0
Brown sharks          Carcharhinus spp.               262    6.9
Yellowfin tuna        Thunnus albacares               185    4.9
Shortfin mako shark   Isurus oxyrinchus               153    4.0
Dolphinfish           Coryphaena hippurus             127    3.4
Shortbill spearfish   Tetrapturus angustirostris      103    2.7
Bigeye tuna           Thunnus obesus                   83    2.2
Black oilfish         Lepidocybium sp.                 51    1.3
Albacore tuna         Thunnus alalunga                 50    1.3
Wahoo                 Acantocybium sp.                 45    1.2
Black marlin          Makaira indica                   43    1.1
Oilfish               Ruvettus sp.                     30    0.8
Thresher sharks       Alopias spp.                     29    0.8
Opah                  Lampris sp.                      16    0.4
Sailfish              Istiophorus sp.                   9    0.2
Porbeagle shark       Lamna nasus                       5    0.1
Total                                               3,781    100

                           Catch                 Catch rate

Common name            Weight    (%)    (kg x 1.000      (ind. x 1.000
                        (kg)          [hooks.sup.-1])   [hooks.sup.-1])

Swordfish              91,155   61.0       587.9             10.8
Blue shark             16,502   11.0       106.4              4.0
Striped marlin         10,012    6.7        64.6              1.9
Brown sharks            8,106    5.4        52.3              1.7
Yellowfin tuna          4,408    2.9        28.4              1.2
Shortfin mako shark     9,311    6.2        60.0              1.0
Dolphinfish               666    0.4         4.3              0.8
Shortbill spearfish     1,236    0.8         8.0              0.7
Bigeye tuna             3,050    2.0        19.7              0.5
Black oilfish             363    0.2         2.3              0.3
Albacore tuna             963    0.6         6.2              0.3
Wahoo                     402    0.3         2.6              0.3
Black marlin            1,300    0.9         8.4              0.3
Oilfish                   215    0.1         1.4              0.2
Thresher sharks         1,000    0.7         6.4              0.2
Opah                      247    0.2         1.6              0.1
Sailfish                  375    0.3         2.4              0.1
Porbeagle shark           188    0.1         1.2              0.0
Total                 149,499    100       964.1             24.4

                        Average
Common name           eviscerated
                      weight (kg)

Swordfish                54.7
Blue shark               26.5
Striped marlin           33.3
Brown sharks             30.9
Yellowfin tuna           23.8
Shortfin mako shark      60.9
Dolphinfish               5.2
Shortbill spearfish      12.0
Bigeye tuna              36.7
Black oilfish             7.1
Albacore tuna            19.3
Wahoo                     8.9
Black marlin             30.2
Oilfish                   7.2
Thresher sharks          34.5
Opah                     15.4
Sailfish                 41.7
Porbeagle shark          37.6
Total

Table 3. Descriptive length statistics of the main species captured in
the study area. LJFL: lower jaw to the fork of the caudal fin.

Tabla 3. Estadisticos descriptivos de talla de las principales
especies capturadas en el area de estudio. LJFL: longitud desde la
mandibula inferior a la horquilla de la aleta caudal.

                                                      LJFL (cm)

Common name           Scientific name              Minimun   Maximun

Yelowfin tuna         Thunnus albacares               65       167
Albacore tuna         Thunnus alalunga                76       135
Black oilfish         Lepidocybium sp.                56       146
Bigeye tuna           Thunnus obesus                  72       201
Dolphinfish           Coryphaena hippurus             80       135
Black marlin          Makaira indica                 125       295
Striped marlin        Tetrapturus audaz              119       319
Shortbill spearfish   Tetrapturus angustirostris     150       263
Shortfin mako shark   Isurus oxyrinchus               97       308
Porbeagle shark       Lamna nasus                    180       220
Swordfish             Xiphias gladius                 75       325
Opah                  Lampris sp.                     98       106
Sailfish              Istiophorus sp.                195       227
Wahoo                 Acantocybium sp.               105       178
Blue shark            Prionace glauca                 50       278
Brown sharks          Carcharhinus spp.              119       263
Thresher sharks       Alopias spp.                   148       235

                          LJFL (cm)

                              Standard
Common name           Mean    deviation     n

Yelowfin tuna         119.8     27.5        191
Albacore tuna         103.4     11.4         52
Black oilfish         108.5     23.7         44
Bigeye tuna           126.8     29.1         81
Dolphinfish            99.4     13.7         57
Black marlin          211.5     29.7         42
Striped marlin        215.0     24.5        227
Shortbill spearfish   170.1     21.3         49
Shortfin mako shark   210.4     34.1        166
Porbeagle shark       200.0     28.3          2
Swordfish             170.2     38.5      1,816
Opah                  102.3      4.0          3
Sailfish              210.6     13.1          7
Wahoo                 141.2     19.0         40
Blue shark            206.4     35.0        580
Brown sharks          182.6     30.0        140
Thresher sharks       190.9     21.6         31
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Title Annotation:Research Article
Author:Vega, Rodrigo; Licandeo, Roberto; Rosson, Gaston; Yanez, Eleuterio
Publication:Latin American Journal of Aquatic Research
Article Type:Report
Date:Mar 1, 2009
Words:7100
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