Stock Assessment And Management Strategy For Metapopulation Of Illex Argentinus

Illex argentinus is an abundant squid resources all over the world.It is also an important target species for Chinese squid jigging.Illex argentinus is abundant between 35°S and 52°S where there are 3 to 4 cohorts.The I.argentinus abundance fluctuate severely among different years.Only a few studies were conducted on its stock assessment and management.Hence,studies of I.argentinus should focus on its stock assessment and management to make scientific management strategies and to realize sustainable utilization of I.argentinus resource.In the present thesis,we use fishery capture data of I.argentinus from China and FAO,combined with Sea Surface Temperature and Chlorophylla,based on General Linear Model(GLM)with spatial autorelation and four distance models(exponential,spherical,Gaussian and linear),for CPUE standardization.The results were compared with the results based on standard GLM to get the most suitable model.The Catch Per Unit Fishing Effort(CPUE)based on the most suitable model was used as the relative resource abundant index of I.argentinus.Then,Schaefer model based on Byesian statistics was used to assess its abundance.Single population and metapopulation were the hypothesized populations for management strategy evaluation.(1)Observational Catch per unit effort(CPUE)data are not independent to each other but have spatial autocorrelation.So far,most of the existing CPUE standardization methods assume that the independency of CPUE in spatial level.In this study,Illex argentinus were selected as case study to explore CPUE standardization based on the fishing data of Chinese jigging fishery and the corresponding data of Sea surface temperature and the Chlorophyll-a in the Southeast Atlantic Ocean from January to May from 2000 to 2014.To compare the effect of spatial autocorrelation on CPUE standardization,generalized linear model(GLM)was chosen as basic model,and the spatial autocorrelation was incorporated into the standard GLM.According to Akaike Information Criterion(AIC)and Bayesian Information Criterion(BIC),spatial-GLM performed better than standard-GLM,and the exponential model generated the best goodness-of-fit to the data among four distance models.Also,the precision of standard GLM were more overestimated than that of spatial autocorrelated GLM.It is recommended for us to take spatial autocorrelation into consideration when GLM is used to standardize CPUE data derived from commercial fisheries based on the present study.(2)Stock assessment and management strategy evaluation of I.argentinus based on single population.Single population is the fundamental hypothesis for the present fisheries stock assessment.In this chapter,we assessed the I.argentinus abundance based on Byesian statistical Schaefer model with single population.The results showed that year capture data and resource abundance index could provide sufficient information for Bayesian stock assessment model.Catch mortality is lower than Flim for single population.Abundance recovers to good condition with decreased catch mortality.Decision analysis showed that the abundance could keep at sustainable level under single population with yield rate at 0.3.Yield rate should be set between 0.2 and 0.3 for conservative strategy,where the sustainable catch is around 800 thousand tones.(3)Stock assessment and management strategy evaluation of Illex argentinus based on metapopulation.However,fishery resource is usually composed of several populations,which also has communication that forms metapopulation.In the present study,we used Bayesian based Schaefer model to assess the biomass of Illex argentinus and analyze management strategy based on metapopulation analysis.The results showed that year catch data and resources abundant index provide lots of information for Bayesian stock assessment model.Predicted model parameter value and max sustainable catch of metapopulation are similar to these of single population.Fishing mortality of single population is lower that limit reference Flim.While fishing mortality of southern population of metapopulation is higher than Flim under some calendar years,and then the biomass recover to good condition with reducing of fishing motality.Decision analysis showed that resource can keep at a good condition with sustainable utilization when the yield rate was set to 0.3 for both single population scheme and metapopulation scheme.Yield rates could be set between 0.2 and 0.3 for conservative management strategy,where the sustainable catch is around 0.8 million tons.