Length-based stock assessment for Procambarus clarkii aquaculture management in China: An alarming of ongoing recruitment overfishing

Abstract

Procambarus clarkii is a commercially significant species both domestically and internationally, and has become the most extensively farmed fishery species in China. However, accurately assessing stocks is often challenging, especially for data-poor fisheries, which undermines effective fishery management. This study aims to identify gaps in the stock status of P. clarkii and provide guidance for effective aquaculture management to promote the sustainability in the P. clarkii aquaculture industry. A total of 2035 crayfish were collected to obtain length-frequency data from March 2016 to February 2017 in the Selection and Reproduction Center of Crayfish, Houhu management area, Qianjiang, China. The seasonally oscillating von Bertalenffy Growth Function (VBGF) was fitted using two optimized ELEFAN approaches (ELEFAN_SA, a simulated annealing algorithm; ELEFAN_GA, a genetic algorithm) to estimate the growth, mortality, and exploitation rates of P. clarkii population. ELEFAN_SA provided a better fit and was subsequently used to derive the following results: an asymptotic total length (Linf) of 130.86 mm, a growth coefficient (K) of 0.63 year−1, initial condition parameter (t0) of −0.32 year−1, expected longecity (tmax) of 4.44 year−1, a total mortality (Z) of 1.96 year−1, a natural mortality (M) of 0.58 year−1, a fishing mortality (F) of 1.38 year−1 and a exploitation rate (E) of 0.70. The Thompson and Bell model estimated the overall stock biomass at approximately 1.92 tons, with the biological reference levels of F0.1 = 0.78 year−1, F0.5 = 0.59 year−1, E0.1 = 0.40, and E0.5 = 0.30. The current F and E (1.38 year−1 and 0.70) exceeded the established thresholds, indicating a high risk of overexploitation of the P. clarkii population. Jones' length-based cohort analysis demonstrated P. clarkii individuals with a total length ranging from 86 mm to 102 mm were more vulnerable to fishing pressure, and that the current fishing selectivity primarily targeted at immature juvenile P. clarkii. The results of GTG-LBSPR model estimated the stock's spawning potential ratio (SPR) at 0.33, which was below the target SPR of 0.4, suggesting a possible ongoing recruitment overfishing. Based on the findings of this study, it strongly advocates for collaborative efforts among researchers, fishery managers, and fish farmers in finding practical and effective measures, such as implementing the size limit for the first capture, that ensure the long-term reproductive capacity and sustainability of P. clarkii populations. Furthermore, it highly encourages moderate fishing pressure on fast-growing and reproductive potential individuals to offset negative impacts of overfishing and promote high SPR and sustainability.