Stock assessment for Atlantic yellowfin tuna based on extended surplus production model considering life history

The modern fishery stock assessment could be conducted by various models,such as Stock Synthesis model with high data requirement and complicated model structure,and the basic surplus production model,which fails to incorporate individual growth,maturity,and fishery selectivity,etc.In this study,the Just Another Bayesian Biomass Assessment(JABBA)Select which is relatively balanced between complex and simple models,was used to conduct stock assessment for yellowfin tuna(Thunnus albacares)in the Atlantic Ocean.Its population dynamics was evaluated,considering the influence of selectivity patterns and different catch per unit effort(CPUE)indices on the stock assessment results.The model with three joint longline standardized CPUE indices and logistic selectivity pattern performed well,without significant retrospective pattern.The results indicated that the stock is not overfished and not subject to overfishing in 2018.Sensitivity analyses indicated that stock assessment results are robust to natural mortality but sensitive to steepness of the stock-recruitment relationship and fishing selectivity.High steepness was revealed to be more appropriate for this stock,while the fishing selectivity has greater influence to the assessment results than life history parameters.Overall,JABBA-Select is suitable for the stock assessment of Atlantic yellowfin tuna with different selectivity patterns,and the assumptions of natural mortality and selectivity pattern should be improved to reduce uncertainties.

Population dynamics modelling with spatial heterogeneity for yellow croaker(Larimichthys polyactis)along the coast of China

As one of the top four commercially important species in China,yellow croaker(Larimichthys polyactis)with two geographic subpopulations,has undergone profound changes during the last several decades.It is widely comprehended that understanding its population dynamics is critically important for sustainable management of this valuable fishery in China.The only two existing population dynamics models assessed the population of yellow croaker using short time-series data,without considering geographical variations.In this study,Bayesian models with and without hierarchical subpopulation structure were developed to explore the spatial heterogeneity of the population dynamics of yellow croaker from 1968 to 2015.Alternative hypotheses were constructed to test potential temporal patterns in yellow croaker’s population dynamics.Substantial variations in population dynamics characteristics among space and time were found through this study.The population growth rate was revealed to increase since the late 1980s,and the catchability increased more than twice from 1981 to 2015.The East China Sea’s subpopulation witnesses faster growth,but suffers from higher fishing pressure than that in the Bohai Sea and Yellow Sea.The global population and two subpopulations all have high risks of overfishing and being overfished according to the MSY-based reference points in recent years.More conservative management strategies with subpopulation considerations are imperative for the fishery management of yellow croaker in China.The methodology developed in this study could also be applied to the stock assessment and fishery management of other species,especially for those species with large spatial heterogeneity data.

Sexual and spatio-temporal variation of Lake Erie Walleye growth and maturity:A consequence of multiple impacting factors

Sexual and spatio-temporal variations have been observed in the life history parameters of many aquatic species and their causes have been related to harvesting pressure and environmental changes.This study aims to explore sexual,spatial and temporal variation in the growth and maturity through weight-at-length,length-at-age,and maturity-at-length relationships for Lake Erie Walleye(Sander vitreus)as a case to test some hypotheses.Hypotheses on whether harvest pressure and environmental changes(both local and global scale)caused the temporal changes of these life history traits were further diagnosed.Sexual and spatio-temporal variations in these life history traits were formulated using mixed-effects models.Our study found that geographic basin,sex,year and cohort all have substantial effects on the growth and maturity of Walleye based on survey data from 1989 to 2015.Multiple factors including water supply of Lake Erie,temperature,fishing pressure of Walleye,and global climate factors were found to correlate with the temporal variations of growth and maturity of Walleye significantly.Our findings should contribute to the future interpretation of Walleye life history variations and population dynamics.The methodology constructed in this study could be applied to explore the heterogeneity and impacting factors for other species in aquatic ecosystems.