CHEN Xinjun, LI Jianghua LIU Bilin LI Gang and LU Huajie

1) College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, P. R. China

2) National Distant-Water Fisheries Engineering Research Center, Shanghai Ocean University, Shanghai 201306, P. R. China

3) Key Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources of Ministry of Education of China, Shanghai Ocean University, Shanghai 201306, P. R. China

Fishery Biology of Jumbo Flying Squid Dosidicus gigas off Costa Rica Dome

CHEN Xinjun1),2),3),*, LI Jianghua1), LIU Bilin1),2),3), LI Gang1),2),3), and LU Huajie1),2),3)

1) College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, P. R. China

2) National Distant-Water Fisheries Engineering Research Center, Shanghai Ocean University, Shanghai 201306, P. R. China

3) Key Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources of Ministry of Education of China, Shanghai Ocean University, Shanghai 201306, P. R. China

The jumbo flying squid (Dosidicus gigas) population was surveyed with the help of Chinese squid jigging vessels off the Costa Rica Dome (4°–11°N, 90°–100°W) in 2009 and 2010. The daily catch ofD. gigasin the two survey cruises ranged from 0 to 5.5 t and was mostly obtained from the areas bounded by 6°–9°N and 91°–94°W and by 6°30′–7°30′N and 96°–97°W. The sea surface temperature in the areas yielding the most catch ranged from 27.5 to 29℃. The sex ratio of the total catch was 3.75:1 (female: male). The mantle length of the squid ranged from 211 to 355 mm (male) and from 204 to 429 mm (female) with an average of 297.9 and 306.7 mm, respectively. In the relationship of the mantle length (mm) and body weight (g) of the squid, there was no significant difference between sexes. The female and male were at a similar maturity, and most individuals are maturing or have matured with a few females being spent. The size (mantle length) and age at the first sexual maturity were 297 mm and 195 d in females, and less than 211 mm and 130 d in males, respectively. Most of the sampled stomachs (70.6%) had no food remains. The major preys of the squids were fish, cephalopods and crustaceans, with the most abundantMyctophum orientaleandD. gigas. The preys in more than 65% of the non-empty sampled stomachs evidenced the cannibalism ofD. gigas. The results improved current understanding of the fishery biology ofD. gigasoff the Costa Rica Dome, which may facilitate the assessment and management of relative fishery resources.

Dosidicus gigas; fishery biology; Costa Rica Dome

1 Introduction

In last two decades, jumbo flying squid,Dosidicus gigas(d’Orbigny, 1835), has evolved as one of the most important species of cephalopod fisheries in eastern Pacific.D. gigasis widely distributed in eastern Pacific on north from California (37°N), on south to Chile (47°S) and on east up to 125°W (Nesis, 1983; Nigmatullinet al., 2001). The highest abundance ofD. gigasusually occurs off Peruvian and Chilean coast in southern hemisphere as well as in Gulf of California and off the western coast of Baja California in northern hemisphere (Markaida and Sosa-Nishizaki, 2003; Liuet al., 2010). Additionally,D. gigasis distributed in the water off Costa Rica Dome with a strong upwelling. Japanese squid jiggers targetedD. gigasin this area obtained a high catch during fall of 1997 (El Ni?o) but a poor catches during fall of 1999 (La Ni?a) (Ichiiet al., 2002) in the water off Costa Rica Dome.

The fisheries biology ofD. gigaswas previously studied in Gulf of California as well as Peruvian and Chilean water (Nigmatullinet al., 2001; Chenet al., 2008). Nigmatullinet al.(2001) found that the population structure ofD. gigaswas complex and comprised of three groups in terms of sizes: 1) the small-sized (130–260 mm in the mantle length (ML) of adult males and 140–340 mm of adult females, mainly in near-equatorial area), 2) the medium-sized (240–420 mm in ML of males and 280–600 mm in of females, widely in the eastern Pacific, and 3) the large-sized (larger than 400–500 mm ML of males and 550–650 nm to 1000–1200 mm of females, mainly in northern and southern periphery, mostly northward of 10°–15°N and southward of 10°–15°S. Off the Costa Rica Dome,D. gigasis one of the most important and highly abundant squid species in marine ecosystem. Ichiiet al.(2002) described the size and maturity of jumbo flying squid in this area. Chenet al.(2013) found that the ML ofD. gigaswas 205–429 mm and the age was no more than 10 months in females and 8 months in males as were indicated by their statoliths microstructure. The maximum absolute daily growth rate and instantaneous growth rate ofD. gigasin ML were reached during its age of 181–210 d and 151–180 d for females and males, respectively. Additionally, Chenet al.(2013) proposedthat the Costa Rica Dome and adjacent waters serve as a potential spawning ground because of the high proportion of mature squid as well as the presence of rhynchoteuthion paralarvae and high primary productivity resulted from the strong upwelling.

At present, little information is available on the fishery biology ofD. gigasin the waters off the Costa Rica Dome. Based on the two scientific surveys ofD. gigasby Chinese squid jigging vessels in the waters off the Costa Rica Dome in 2009 and 2010, the present study aimed to identify the environmental variables that influence the spatial distribution ofD. gigasand to provide information on the population structure, maturity, and feeding characteristics of this squid species, further improving understanding of the biology ofD. gigasoff the Costa Rica Dome. The information derived in this study is critical for quantifying the population dynamics of this squid and is of guiding significance to the assessment and management of this important marine resource.

2 Materials and Methods

The two surveys ofD. gigaswere carried out with the two Chinese squid jiggers, Fenghui 16 and Zhe Yunyu No 807 (Table 1). Sampling stations were pre-selected and defined by 30’×30’ longitude and latitude. The final sampling positions were defined as the actual sites whereD. gigaswere caught (Fig.1). A total of 565 individuals were randomly sampled from the catch and taken to the laboratory. The sampling location, water temperature, and salinity at different water depths from surface to 300 m deep were measured with Sea-birds (SE-37). The number of jig lines in use (15–20 jiggers per line), fishing depth, time at the beginning and end of each drift, and total catch were recorded.

The dorsal ML (to 1 mm) and body weight (BW, to 10 g) were measured for all samples. The sex was identified and the maturity was evaluated with naked eyes following method described early (Lipinski and Underhill, 1995). The maturity was graded into the five stages,i.e., I–II, immature; III, maturing; IV, mature; and V, spent. Major preys in the stomach contents were identified based on laboratory analysis of undigested tissues. The degree of stomach fullness was recorded using the following scales: 0–empty; 1–little content and less than 1/5 full; 2–less than half full; 3–more than half full; and 4–full (Chenet al., 2007). The daily ages of females and males were determined by the statoliths microstructure,i.e., 130–289 d and 130–240 d, respectively (Chenet al., 2013).

The BW-ML relationship was quantified using the following equation:

whereWis the BW, andaandbare two parameters to be estimated. Logarithm transformation was applied to the equation and the parametersaandbwere estimated using the linear least squares method (Ricker, 1975). The method of analysis of variance (ANCOVA) was used to test the difference between sexes.

Table 1 Key parameters of the squid jigging survey vessels

Fig.1 The two survey areas covered by the Chinese squid jigger vessels off the Costa Rica Dome in 2009 and 2010.

All individuals were examined to determine the ML and age at which 50% squid were mature (referred to as‘size at first maturity’ or ‘ML50%’, and ‘a(chǎn)ge at first maturity’ or ‘Age50%’). The change in the proportion of mature individuals with length or age was fitted to the logistic model with the least squares method (Liuet al., 2010), in which,

wherePiis the relative frequency of mature individuals in length classMLiorAgei,canddare the regression constants, and ML50%(or Age50%) =c/d. Data analysis was performed in SAS (Version 9.1).

3 Results

3.1 Catch and Its Relationship with Environmental Factors

During the two surveys, the daily catch (CPUE) ofD. gigasranged from 0 to 5.5 t with no bycatch. The total catch was 95.5 t and the average CPUE reached 0.72 t. Overall, 75.7% of the fishing days had the CPUE lowerthan 1 t, and 17.4% of the fishing days had CPUE more than 2 t. The catch mainly came from the areas bounded by 6°–8°N and 95°30′–97°W, and by 6°–9°N and 91°–95°W (Fig.2). The high density ofD. gigasappeared in the above two areas under different environmental conditions (Table 2).

In the fishing area of 6°–8°N and 95°30′–97°W and during the period from July to September, surface water temperature ranged from 27.5 to 29.0℃, from 14.0 to 15.0℃ at the depth of 50 m and from 13.0 to 13.7℃ at the depth of 200 m. The corresponding water salinity ranged from 33.4 to 33.9, from 34.8 to 34.9 and from 34.8 to 34.9, respectively (Table 2). In the fishing area of 6°–9°N and 91°–95°W and during the period from February to March, water temperature and salinity were 28.0–29.0℃and 33.8–33.9 on the surface, 24.0–25.0℃ and 34.3–34.4 at the depth of 50 m, and 15.0–17.0℃ and 34.7–34.8 at the depth of 200 m, respectively (Table 2).

Fig.2 The spatial distribution of daily catch of D. gigas in the 0.5°×0.5° latitude and longitude off the Costa Rica Dome in 2009 and 2010.

Table 2 Summary of the survey areas and sample collection of D. gigas

3.2D. gigasPopulation Structure

In total, the sex ratio of the catch was 3.75: 1 (female: male), significantly higher than the expected (1: 1;P＞0.05). The ML of males ranged from 211 to 355 mm with a mean of 297.9 mm and that of females ranged from 204 to 429 mm with a mean of 306.7 mm. The BW of males ranged from 170 to 1050 g with a mean of 615 g and that of females ranged from 240 to 2120 g with a mean of 712 g. The majority (72.5%) of the males were 280–340 mm in ML while the majority (73.8%) of females were 260–360 mm in ML (Fig.3a). A similar range was observed for BW, the majority (78.0%) of the males were 400–800 g and the majority of females (71.6%) were 400–1000 g (Fig.3b).

Fig.3 The mantle length (a) and body weight (b) composition of female and male squid.

3.3 ML-BW and ML-Somatic BW Relationship

Fig.4 The relationship between body weight and mantle length of male (a) and female (b) squid.

The ML (cm)-BW (g) relationship of the samples collected were estimated as

for males (Fig.4a), and

for females (Fig.4b), respectively. There was no significant difference in the BW-ML relationship between sexes (P＞ 0.05).

3.4 Maturity

The maturity of the squid was different between sexes (Table 3). In males, 81.4% of the total were at stage IV, 15.2% at stage III, and 3.4% at stage II. In females, 42.4% of the total were at stages I–II, 40.1% at stage III, and 26.6% at stage IV (Table 3). There were only 0.9% of the females at stage V (Table 3). For a given size, males were more likely to be mature than females (Table 3).

Table 3 Composition of the sexual maturity stages of female and male D. gigas

Female ML50%estimated was 297 mm and Age50%was 195 d. The change in the proportion of mature females with size and age (Fig.5) were described by the following equations:

Fig.5 The size (a) and age (b) at first maturity of female squid.

For males, the relationship between the proportion of maturity and the size and age could not be quantified with logistic models because immature males were lacking, and ML50%or Age50%was not estimated. However, we believe that the size and age at first maturity of males should be smaller or younger than those of the smallest specimen in this study (i.e., 211 mm and 130-day-old, respectively) because only 2 immature males were found in the catch.

3.5 Diet

The stomachs analyzed rarely had food remains and on average 70.6% of the stomachs were empty. Regarding the fullness stages, 19.9% and 8.1% of the samples were graded to stage 1 and 2, respectively, while only 1.4% of the total samples were graded to stage 3.

The stomach contents included three major prey groups: fish, cephalopods and crustaceans, which represented 55.8%, 38.1%, and 6.1% of the stomach contents by weight, respectively. The species remains in the stomach contents were identified as Myctophidae, Sardinella, andD. gigas. Approximately 65% of the stomachs showed the evidence of cannibalism. However, cannibalism was much greater for the squids caught in the light field around the survey vessel, and small squid (ML＜10 cm) were often attacked by large-sizedD. gigasaround the squid jigging vessels in the fishing area of 6°–8°N and 95°30′–97°W during August to September.

4 Discussion

4.1 CPUE Distribution and Its Relationship with Marine Environment

The results from this study showed thatD. gigaswas widely distributed in the survey area, and that the majority of the catch came from the areas defined by 6°–8°N and 95°30′–97°W and by 6°–9°N and 91°–95°W. Our results were consistent with the previous (Ichiiet al., 2002) despite the distribution density ofD. gigasvaried. Ichillet al. (2002) reported that the fishery operation forD. gigaswas conducted in the waters of 7°–9°N and 92°–100°W from June through November in 1997, and the monthly average CPUE (tonnes per vessel per day) was 19.4 tonnes in August, 15.2 tonnes in September, and 8.5 tonnes in October. In 1999, the fishery was only conducted in the same fishing areas from August to September and the monthly average CPUE was low, 3.1 tonnes in August and 2.3 tonnes in September. The jumbo flying squid abundance within the 200 nautical miles exclusive economic zone of the Costa Rica Dome was unknown because the fishery was not permitted.

The distribution ofD. gigaswas closely related to sea surface temperature (SST) and its optimal SST ranged from 27.5 to 29℃ in the waters off the Costa Rica Dome. Ichiiet al.(2002) found that SST was warmer throughout the fishing areas in October 1997 (El Ni?o) and August to September of 1999 (26–30℃) but was cooler in October 1999 (La Ni?a) (22–26℃). The oceanographic conditionsof this fishing ground are not the same as those in the southeastern Pacific. Ichiiet al.(2002) found that a high abundance of squid occurred in association with the well-developed countercurrent ridge (upwelling) off the Costa Rica Dome during fall 1997, but not during fall 1999 when the countercurrent ridge was less developed. In the southeastern Pacific, the fishing ground of squid was likely formed as a result of the upwelling from Peru Current. Waludaet al.(2006) reported that the high density ofD. gigastook place in waters with SST of 17–22℃in the Peruvian waters. Liuet al.(2010) found that the suitable SST forD. gigaswas 17.5–21℃ on the northern fishing ground (20°–30°S) and 14–16℃ on the southern fishing ground (37°–41°S) off Chilean waters. Therefore, we concluded that SST greatly influenced the spatial distribution and abundance ofD. gigas, which was in agreement with the results obtained in previous studies (Anderson and Rodhouse, 2001; Nigmatullinet al., 2001).

4.2 Population Structure

The intraspecific structure ofD. gigasin the eastern Pacific is complex (Nigmatullinet al., 2001). There are many local, sometimes allopatric but mostly sympatric and parapatric groups, which differ from each other in a variety of important ecological aspects. The distributional ranges of both the small- and medium-sized groups overlap fully or partially, and the small-sized group is found predominantly in the equator adjacent area (Nigmatullinet al., 2001). Ichiiet al.(2002) found the same pattern in October 1997 and 1999, that is, ML of jumbo flying squid ranges from 16 to 35 cm (mostly between 17 and 28 cm) in October 1997, and from 15 to 39 cm (mostly between 18 and 29 cm) in October 1999. The size of our samples ranged from 204 to 429 mm in ML, likely covering the possible size range of this species. Within the Gulf of California, the population structure ofD. gigaswas complex and consisted of three groups of different sizes at maturity (Markaida, 2006). It is unknown if theD. gigasstock off the Peruvian and Chilean coast is the same population of squid that inhabits the Gulf of California and off the Costa Rica Dome in the north of the equator.

4.3 Sex Ratio and Maturity

Ichiiet al.(2002) found that female squid was dominant in the catch in 1997 and 1999, accounting for 90%–94% of the total population with 5%–15% of the female samples copulated. There was a tendency that mature and large females were more frequently distributed toward southern areas in both years. Of the samples collected in two surveys in the present study, female squid accounted for 79.0% of the total, lower than that obtained by Japanese squid jigger in 1997 and 1999. In our survey, the medium-sized squid jigger with three lines of 1.3 mm in diameter was used. Thus, it is less likely to catch the small-sizedD. gigas, mostly males, compared with large individuals. The observed skewed sex ratio could be attributed to the selectivity of fishing gears.

We found that maleD. gigasmatured at smaller sizes than the females did, as is commonly described in cephalopods (González and Guerra, 1996). However, the size range of mature male and femaleD. gigasin this study differ from that found in other waters. Tafuret al. (2001) reported that the male squid had a size at first maturity of 136–474 mm during 1991 to 1995, and that the range of size at first maturity of female squid was 285–327 mm in the Peruvian waters. Hernandez-Herreraet al. (1998) and Markaidaet al. (2004) showed that theD. gigaspopulations within the Gulf of California matured at a larger size, 510 mm in females and 420 mm in males. Liuet al. (2010) found that the size at first maturity was 638 mm ML in females and 565 mm ML in males in the waters off EEZ of Chile. The difference in the size at first maturity among fishing areas can be related to the different geographical populations or spawning populations. Alternatively, the size at first maturity ofD. gigasmay vary with environmental conditions as well. Argüelles and Tafur (2010) described the inter-annual variability of the size at maturity, somatic and reproductive investment of mature males, and females ofD. gigasduring the spawning peak (October–March) during 1994–2006 in the Northern Humboldt Current Ecosystem (Peruvian waters).

4.4 Growth and Diet

Significant difference was found in the slope of logarithmic length-weight relationship between the results of this study and the previous. The parameter (b) of the length-weight relationship was smaller than that reported by Ibanez and Cubillos (2007) in central-south Chile in 2003–2004 (b=3.2 for both sexes), and by Chenet al.(2010) off EEZ of Chile in 2006–2008 (b= 2.8036 for males, andb=3.1446 for females). These parameters are different from those of purpleback flying squid,Sthenoteuthis oualaniensis, near the equator of the northwest Indian Ocean (b= 2.9115 for females, andb=2.5842 for males; Chenet al., 2007).

High occurrence of cannibalism in the diet of the squid in the study area (＞65%) proved thatD. gigasis a species with high cannibalistic feeding. This result is consistent with previous findings in the Gulf of California (Markaida, 2006). In the present study, myctophids, mainlyMyctophum orientale, were predominant in the waters off the Costa Rica Dome.D. gigasis a predator-opportunist, whose feeding spectrum is different with sizes and regions (Wang and Chen, 2005). The feeding habits ofD. gigaschange during ontogeny with a shift in preference from crustaceans to fish, and the prey size increases as the squid grows (Schchetinnikov, 1989). The prey size, on average, is 5–7 cm and occasionally larger than 10–15 cm for large adult squid (Markaida and Sosa-Nishizaki, 2003). In addition, diet varies by location and is dominated in different places, by mesopelagic fishes such asBenthosema panamense,Triphoturus mexicanus, andVinciguerria lucetiain the Gulf of California and adjacent waters (Markaida and Sosa-Nishizaki, 2003).

In summary, we have surveyed theD. gigaspopulation in two cruises in 2009 and 2010. The results greatly improved our understanding of fishery biology ofD. gigasoff the Costa Rica Dome and may guide the assessment and management of relative fishery resources. Further studies are needed to investigate the spatial and temporal variability in the distribution and migration, population structures and key biological parameters ofD. gigasin the waters off the Costa Rica Dome as well as the California and Peruvian waters and to identify the key habitat requirements of this important marine species.

Acknowledgements

The authors would like to thank the anonymous reviewers for their making valuable comments resulting in significant improvements of the manuscript. The authors also thank the supports of the two scientific surveys made by Fenghui No 16 and Zhe Yunyu No 807. This work was funded by National Nature Science Foundation of China (NSFC 41276156), National High-tech R&D Program of China (863 Program; 2012AA092303), Project of Shanghai science and technology innovation (12231203900), Industrialization program of National Development and Reform Commission (2159999), and Shanghai Leading Academic Discipline Project. Also this study was supported by National Distant-water Fisheries Engineering Research Center.

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(Edited by Qiu Yantao)

(Received September 26, 2012; revised November 4, 2012; accepted August 26, 2013)

? Ocean University of China, Science Press and Spring-Verlag Berlin Heidelberg 2014

* Corresponding author. Tel.:0086-21-61900306

E-mail:xjchen@shou.edu.cn