| The jumbo flying squid, Dosidicus gigas, is widely distributed throughout the Eastern Pacific Ocean from California(37°N) south to the southern part of Chile(47°S). It is the largest and one of the most abundant species of the family Ommastrephidae. And it plays a critical role in ocean ecosystem. In order to ensure the efficient and reasonable development and scientific ma nagement, in this study, growth, population structure, habitat environment and life history of D. gigas were studied by analyzing the microstructure and microchemistry of statoliths and beaks. This study may provide scientific basis for the sustainable development of fishery resources.Based on the samples collected by the help of Chinese jigging vessels between 2009 and 2014 off the Peruvian Exclusive Economic Zone(EEZ), the age of D. gigas was estimated by analyzing the increments of statolith and beak microstructure. And the age, growth and population of D. gigas were studied using beak microstructure. The morphometry of beaks was analyzed and the relationship between morphometric parameters of beaks and mantle length, body weight and age were built. Mea nwhile, the effect of individual growth on beak morphology was analyzed. The relationship between beak pigmentation stage and growth of D. gigas was studied using BP neural network. Moreover, the effect of beak pigmentation process on the diet change of D. gigas was primarily discussed. The LA-ICP-MS(Laser ablation inductively coupled plasma mass spectrometry) was applied to determine the trace elements concentrations of statoliths and beaks at different growth stages of D. gigas. The deposition synchronism of trace elements in statolith and beak was analyzed and the different spawning populations were divided using trace elements of early ontogenetic statolith and beak, respectively. The results of this study could be summarized as follows:(1) Beak microstructure and determination of growth increments. The increments in the dorsal region of the beak’s hood were more completed. And to avoid the tip erosion effects, the first increments could be counted in the dorsal area of the rostral sections. This study found that the microstructures of the upper and lower beak were very similar, and both of them contained longitudinal increments and internal rostral axis. However, in terms of the mophology and the pigmentation process, there are differences between the microstructures of upper and lower beak. Results indicated that the growth increments of the upper and lower beak obtained were lineally related with that of the statolith. Values of r2 and slope close to 1 were obtained(P<0.01). Results indicated that both of the microstructures of the upper and lower beak can better estimate the age of the Jumbo flying squid. And the beak should be widely used in the research of age and growth of cephalopod.(2) The age and spawning population of D. gigas based on the beak. The ages were estimated by analyzing the beak microstructures of D. gigas caught off the Peruvian Exclusive Economic Zone(EEZ) from July to October in 2013. The mantle length(ML) of the samples ranged from 204 to 396 mm, and the age was estimated from 123 to 298 days for females and from 106 to 274 days for males. Back-calculated hatching dates were from December 2012 to May 2013. All of the samples were austral summer/autumn spawning cohort. Meanwhile, there was a hatching peak of D. gigas between January an March. Growth in ML and body weight(BW) were best described by exponential functions and there were no significant differences between females and males. Growth rates of ML and BW were similar between females and males, and the maximum absolute daily growth rates and instantaneous growth rate were 2.12 mm/d and 0.59, respectively. This research suggests that the upper beak could be used to study age, growth and population structure of D. gigas. In addition, growth and population structure vary according to season and geographic area.(3) Morphology of the beak and its influencing factors. Among the 12 beak morphometric parameters, the values of correlation coefficients were very high between upper crest length, upper rostrum length, upper lateral wall length, lower crest length, lower lateral wall length, lower wing length and mantle length, body weight and age. The relationship between beak morphometric parameters and mantle length were best described by linear models, and it was significantly different between females and males. The linear functions were best used to describe the relationship between beak morphometric parameters and age, and there was no significant difference between females and males. Except upper lateral wall length, other beak morphometric variables and body weight were best fitted by power models and was no difference between females and males. The principle component analysis showed that the contribution rate of the first principle component of upper and lower beak morphomephy were 95.69% and 95.11%, respectively. The maximum load coefficients of the beak morphometric variables were upper crest length and lower lateral wall length. The Least Significant Difference(LSD) analysis showed that the growth of beak between females and males varied according to mantle length, age and sex maturity. The growth had differences among the sections of beak of same sex individuals. However, if the mantle length is greater than 400 mm, the age of female is greater than 300 days, the age of male is greater than 200 days or the sex maturity stage is greater than stage 3, then the growth of beak is slow. Results indicated that the values of correlation coefficients were very high between beak morphometric parameters and mantle length, body weight a nd age. And the beak can be used to estimate the size, biomass and age of D. gigas. The morphometry of beak should be influenced by body size, age and sex maturity.(4) Beak pigmentation development of Dosidicus gigas and its influencing factors. The relationship was built between beak pigmentation stage and age, mantle length(ML), body weight(BW), sexual maturity stage(SMS) and morphometric parameters of beak using BP neural network. Results showed that the main factors influencing the beak pigmentation stage were age, body weight, sexual maturity stage, upper rostrum length and lower wing length, and their contribution rates were 7.44%, 7.40%, 9.14%, 7.88% and 9.07%, respectively. The beak pigmentation stage increased with age, mantle length, body weight and morphometric indices of beaks, and the relationships were significantly positive. Meanwhile, the beak pigmentation degree increased with the sexual maturity stage. Results indicated that the relationship between pigmentation process and growth of D. gigas and its beak was close. The pigmentation development could not only reflect the growth of D. gigas but also reflect the change of diet.(5) The element composition of beak and statolith and population classification. The LA-ICP-MS was used to determine the trace elements concentrations of statoliths and beaks at different growth stages of D. gigas. Except for Na/Ca and Ba/Ca, the other trace elements in statoliths and beaks showed no significant correlation. Mg/Ca decreased progressively from the nucleus to the edge. This trend might reflect the growth rate of statolith. The concentration of Sr was probably influenced by several factors. Ba/Ca increased from postnuclear zone to the edge, which confirmed that paralarvae and juvenile squid inhabit surface waters, while subadults and adults migrate into deeper and colder waters. P/Ca of beaks decreased from subadult to adult, which might reflect squids migrate into deeper waters. The trace elements in statoliths and beaks of early ontogenetic stages of different spawning population were measured. This study suggest that Sr/Ca and Ba/Ca in early ontogenetic statolith could be used to discriminate different spawning populations. Sr/Ca in embryonic statoliths is mainly influenced by genetic factors, while Ba/Ca in embryonic statoliths is probably not only influenced by genetic factors but also influenced by external environmental factors. And it is turned out that Ba/Ca has negative correlations with ambient temperature. Compared with Sr/Ca, Ba/Ca could better reflect the change of temperature. Zn/Ca in early ontogenetic beak had significant differences between spawning populations. And Zn/Ca was selected to discriminate different populations, which had a high classification rate. This study believe that ambient temperature is probably an vital factor affecting the deposition of Zn. |
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