| The neon flying squid, Ommastrephes bartramii, belongs to Cephalopoda, Coleoidea, Teuthoidea,Oegopsida, Ommastrephidae,Ommastrephes, is widely distributed in temperate and subtropical waters of Pacific, Indian and Atlantic Oceans, and live in surface to 1500 m water layer of the ocean. North Pacific is the main commercially exploited waters of neon flying squid, and also the main fishing waters of Chinese jigging vessels. O.bartramii is important prey of large fishes, seabirds and marine mammals and mainly prey on small fishes, cephalopods and crustaceans, which establish its important role in marine ecosystem.O.bartramii consists of two geographical cohorts, eastern cohort and western cohort. Beaks are the feeding issues of cephalopod. Beaks own characteristcs of morphological stability, good information storage and corrosion resistance, which makes it important carrier of O.bartramii ecological information. According to the samples of the neon flying squidcollected by Chinese jigging vessels during May to November in 2010 in the North Pacific Ocean, we analyze morphology of beaks, growth characteristics of beaks and stable isotopes of beaks to compare eastern and western cohorts, which can provide theoretical foundation for rational exploitation, scientific assessment and management of O.bartramii in North Pacific Ocean. The main results are as follows:(1) Comparison of general biology of O.bartramii. Studies showed that range of mantle length of eastern cohort are larger than that of western cohort. In eastern cohort, range of mantle length of female O.bartramii was 208 to 516 mm, dominant V mantle length of female O.bartramii was ranged from 321 to 410mm; range of mantle length of male O.bartramii was 220 to 280 mm, dominant mantle length of male O.bartramii was ranged from 231 to 250 mm. In western cohort, range of mantle length of female O.bartramii was 187 to 433 mm, dominant mantle length of female O.bartramii was ranged from 201 to 290mm; range of mantle length of male O.bartramii was 163 to 356 mm, dominant mantle length of male O.bartramii was ranged from 201 to 290 mm. In eastern cohort, there is two crests in histograms of mantle length and body weight of female squid, while male only has one, which means female has two small cohort and male has one cohort. In western cohort, there is only one crest in histograms of mantle length and body weight of female and male squid, which means they are the same cohort.There were large quantity variance between female and male of eastern cohort, while western cohort had similar quantity. Sex ratio was 7.12:1 for eastern cohort and 0.98:1 for western cohort, which can be explained by different migration route of two cohorts. Relationships of mantle length and body weight showed that parameter b were more than 3 and R2 were more than 0.9 except eastern cohort male individuals(b<3, R2=0.69).According to growth increments of squid statolith, age range of female squid of eastern cohort was 160 to 399 d, that of male was 157 to 277d; age range of female squid of western cohort was 108 to 301 d, that of male was 107 to 267 d. In eastern cohort, relationship between mantle length and age of female squid present logarithmic curve, while that of male squid present exponential curve; relationship between body weight and age of female squid present power function, while that of male squid present exponential curve. In western cohort, relationship between mantle length and age of squid present linear function, while relationship between body weight and age of squid present exponential curve. In eastern cohort, hatching months of female squid were April to January of the following year, and that of male squid were August to January of the following year, which means the eastern cohort belongs to fall cohort. In western cohort, hatching months of female squid were December to July of the following year, and that of male squid were January to July, which means VI the western cohort belongs to winter-spring cohort. Comparing two cohorts, we found that the maximum age of eastern cohort of female squid is longer than that of western cohort, which corresponds to the mante length. While the maximum age of eastern cohort of male squid is shorter than that of western cohort, which can be explained by small range of mantle length and body weight of eastern cohort of male squid.We also found that growth rates of mantle length of eastern cohort of female squid declined steadily, while growth rates of body weight ascended between 161 to 325 d, declined suddenly between 325 to 355 d and ascended again at last. Growth rates of mantle length and body weight of eastern cohort of male squid ascended steadily. Growth rates of mantle length of western cohort fluctuated a lot, and growth rates of body weight ascended steadily.(2) Comparison of morphological and growth characteristic of beaks. T-test showed that there were significant variance between female and male of eastern cohort in morphology of beaks, while there were no significant variance in western cohort(except UCL, LHL and LCL). Comparing two cohorts, we found that there were significant variance between them(except UWL, LCL, LRL and LRW of male).Comparing relationships of mantle length and 12 morphological parameters, the best fittings were UCL, ULWL, LLWL and LWL in eastern cohort, where female were all power function and male were different(linear: UCL and ULWL, exponential: LLWL, power: LWL). The best fittings were UHL, ULWL, LCL and LLWL in western cohort, where female were all linear function and male were different(linear: ULWL and LLWL, exponential: UHL and LCL). Comparing relationships of body weight and 12 morphological parameters, the best fittings were UCL, ULWL, LLWL and LWL in eastern cohort, where female were all power function and male were different(linear: ULWL and LLWL exponential: UCL and LWL). The best fittings were UHL, ULWL, LCL and LLWL in western cohort, where female and male were all exponential function.PCA found that UCL and LLWL can represent growth of beaks of eastern cohort of female squid, while URL, ULWL and LHLcan represent that of male squid.UHL, UCL, ULWL and LLWL can represent growth of beaks of western cohort of female squid, while UHL, UCL, ULWL and LLWLcan represent that of male squid.Using 10 morphological parameters(UHL, URL, URW, ULWL, UWL, LHL, LCL, LRW, LLWL and LWL) to establish discrimination functions, we found that accuracy rate of eastern cohort was 77.4%, and that of western cohort was 92.7%, which proved that discrimination functions can distinguish two cohorts well.Growth rates of eastern cohort of O.bartramii beaks declined in general, the maximum appeared at 191 to 220 d and the minimum appeared at 341 to 370 d. While growth rates of western cohort of O.bartramii beaks declined after ascended, the maximum appeared at 161 to 190 d and then declined after that.(3) Comparison of stable isotopes of O.bartramii beaks. Stable isotope values of eastern cohort had significant variance(P<0.01), while that of western cohort had no significant variance(P>0.05). There were significant variance in δ13C between upper beak and lower beak of both cohorts(P<0.01), while there were significant variance in δ15N(P>0.05). There were significant variance in δ13C and δ15N between eastern and western cohorts. Carbon nitrogen ratio of upper beak was larger than lower beak.We also found that the relationships of mantle length, body weight and δ13C of both cohorts were linear, while the relationships of mantle length, body weight and δ15N were logarithmic.The relationships between pigmentation stage and stable isotope values of both cohort were logarithmic. |
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