| Dosidicus gigas,one of the largest pelagic species of cephalopods,is mainly found in the tropical and subtropical regions of the eastern Pacific Ocean,with an abundant distribution from the continental shelf to open waters 550-750 km away from the coastline.D.gigas is one of the three main fishery resources in Latin America,fished mainly in Mexico,Peru and Chile,with total commercial annual catches ranging from650,000 to 900,000 tons from 2006-2016.The influence of D.gigas on the marine ecosystem cannot be ignored,being both an important predator and the most important food source for marine mammals such as seals and whales.Scholars both at home and abroad have made numerous studies on the relationship between the population structure,age and growth,and reproductive characteristics of the cephalopods and the marine environment.However,as a short-lived cephalopod,its key life history processes are highly susceptible to external environmental changes,and it is an important scientific issue to grasp and understand the response of the life history processes of D.gigas to changes in the marine environment,which can help to scientifically conserve and manage the stem fish resources.The statolith is one of the important hard tissues of D.gigas,containing critical information about its entire life history.Therefore,in this study,biological characteristics of D.gigas were statistically analyzed based on samples collected in different climate years off Peru.Differences in growth between years were compared,and changes in fishery biology information such as body length and sex maturity under climate events were analyzed to explore the effects of climate change and ocean environmental changes on the biological characteristics of D.gigas over long-time series.Statistical analysis was also conducted on the sex maturity,initial sexual maturity body length,and gonadal index and body length relationship of D.gigas samples collected in different years to investigate the effects of climate change and ocean environmental changes on their reproductive characteristics.The statoliths of D.gigas samples from abnormal climate years and normal years were cleaned,ground,polished,and their microstructures were photographed and recorded.Their age was calculated based on the growth rings of the statolith,and the effects of climate change and ocean environmental changes on the age and growth of D.gigas over a long-time series were explored.The following research results were obtained:(1)Interannual variation of population structure of D.gigas off Peru.Based on7,514 D.gigas samples collected from off Peru from 2008 to 2020,the fishery biological characteristics of individual weight and mantle length were analyzed to explore their response to marine environmental factors.The study results showed that there were significant differences(P<0.05)in mantle length and body weight relationship between males and females in different years,with small and medium-sized groups being dominant in 2008-2010 and 2019-2020,while small-sized groups dominated in other years,and a few large individual samples were found in certain years.El Ni(?)o events suppressed the growth of D.gigas and produced smaller-sized groups,while La Ni(?)a events favored the growth of medium to large-sized groups.During 2008-2020,the mantle length of small-sized groups decreased by 46 mm,while that of medium-sized groups increased by 28 mm.The b-value of the growth parameter was positively affected by La Ni(?)a events to a greater extent(2010>2020>2011),but a negative impact was observed in El Ni(?)o years(2009>2015),indicating a significant negative correlation between the b-value and sea temperature.Correlation analysis showed that the Ni(?)o index was negatively correlated with mantle length of D.gigas for the previous and current years.The study concluded that the changes in climate during 2008-2020 had a significant impact on the population structure of D.gigas off Peru.(2)Interannual variation of reproductive characteristics of D.gigas off Peru.This study analyzed 7514 D.gigas samples collected by Chinese squid fishing vessels during production in the offshore waters of Peru from 2008 to 2020,and conducted statistical analysis on the relationship between the sexual maturity of different year samples,the first sexual maturity mantle length,the gonadosomatic index and mantle length changes to explore the impact of climate change on the reproductive characteristics of D.gigas in a long time series.The study found that females matured later,and sexually mature individuals mainly appeared in medium-sized groups from 2008 to 2020.Males matured earlier,and except for 2011,sexually mature individuals were present in small groups in other years.Both males and females exhibited precocious sexual maturity in response to long-term changes in the marine environment,and mantle length at first sexual maturity decreased for both sexes,with a decrease of 201.2 mm for females and143 mm for males.High temperatures accelerated the sexual maturity rate of jumbo flying squid,resulting in more sexually mature small individuals,while low temperatures delayed sexual maturity,resulting in more sexually mature large individuals.After 2011,the reproductive capacity of female individuals showed a decreasing trend,while the gonadosomatic index of male individuals did not change significantly.(3)The effect of climatic stress on the early life history of D.gigas on their later individual growth.In this paper,In this paper,we analyzed mantle length and age structure,mantle length-body weight relationship,age at first sexual maturity,and growth rate of adult individuals experiencing different climatic conditions during paralarve and juvenile stages,based on samples of D.gigas collected off Peru from 2008 to 2010.The results of the study showed that there was no significant difference between paralarve and juvenile stages of D.gigas samples experiencing different climatic conditions(P>0.05),and there was a significant difference in the age of maturity and mantle length of adult D.gigas samples experiencing different climatic events during paralarve and juvenile stages(P<0.05);The age at first sexual maturity of individuals experiencing different climatic events in paralarve and juvenile stages were all La Ni(?)a years > normal years >El Ni(?)o years;the Absolute growth rate(AGR)and Instantaneous relative growth rate(G)of individuals experiencing different climatic events in paralarve and juvenile stages were highest at ages 301-330 days,with 1.67 mm/d,2.13 mm/d,1.87 mm/d and 0.41%/d,0.56%/d and 0.45%/d,respectively;Individuals that experienced El Ni(?)o events during paralarve and juvenile stages grew to a smaller mantle length and age and matured sexually earlier,while those that experienced La Ni(?)a events during paralarve and juvenile stages grew to a larger mantle length and age and matured sexually later.It was concluded that sea surface temperature changes experienced during paralarve and juvenile stages did not directly affect the growth of adult D.gigas,but rather a combination of factors such as feeding,incubation time and photoperiod. |
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