Length-Based Assessment of Fish Stocks in a Data-Poor, Jointly Exploited (China and Vietnam) Fishing Ground, Northern South China Sea

Zirong Huang,Kui Zhang,Gang Hou,Jiajun Li,Dengfu Shi,Yongsong Qiu,Zuozhi Chen

doi:10.3389/fmars.2021.718052

Abstract

The Beibu Gulf is one of the most important fishing grounds in the South China Sea (SCS), and the fisheries resources in this area are exploited by both China and Vietnam. In recent decades, some indications of overfishing have appeared, including declining catch rates, frequently changing catch composition, and shrinking body sizes in main commercial fish species. Due to limited data availability, only a small subset of exploited fish stocks in this area has been assessed. Here, we applied two length-based methods, electronic length frequency analysis (ELEFAN) and length-based Bayesian biomass estimation (LBB), to stock assessment of nine exploited fish species in the Beibu Gulf. There were total 53, 652 length records of 30 target stocks used in this study during the survey period from 1960 to 2015. The results showed that the two length-based methods presented different ability in estimating exploitation rate (E), and the estimated E ranged from 0.34 to 0.87 using ELEFAN method while ranged from 0.26 to 0.86 using LBB method. The prior information from ELEFAN method was effective for LBB method, as there were significant differences in 66.7% of the 30 target stocks in estimated Linf, and 93.3% in estimated B/BMSY, using LBB method with and without prior information. The estimated Lc/Lc_opt and B/BMSY of LBB method suggest a pressing situation for the fisheries in the Beibu Gulf, as 86.7% of the 30 target stocks had been suffering from growth overfishing (Lc/Lc_opt &lt; 1), and 83.3% had been overexploited or fully exploited (B/BMSY ≤ 1.2). In addition, we suggest using both ELEFAN and LBB methods to fit length-frequency data of data-poor fish stocks because they are complementary in estimating management reference points. We also emphasize collaboration mechanism should be established by China and Vietnam for the sustainability and recovery of fishery resources in the Beibu Gulf.

Highlights

Marine fisheries resources are an important source of animal protein and micronutrients, and provide employment opportunities and income for people worldwide [Food and Agriculture Organization (FAO) (2016); Pauly and Zeller, 2016]
The results showed that the two length-based methods presented different ability in estimating exploitation rates, and the prior information from electronic length frequency analysis (ELEFAN) method was effective for length-based Bayesian biomass estimation (LBB) method
The estimated Lc/Lc_opt and B/be above the MSY level (BMSY) of LBB method suggest a pressing situation for the fisheries in Beibu Gulf, as 86.7% of the 30 target stocks had been suffering from growth overfishing, and 83.3% had been overexploited or fully exploited

Summary

Introduction

Marine fisheries resources are an important source of animal protein and micronutrients, and provide employment opportunities and income for people worldwide [Food and Agriculture Organization (FAO) (2016); Pauly and Zeller, 2016]. Most of exploited fisheries, especially in developing countries, do not have the data required for traditional methods and are considered data-poor. Only 20% of global catch comes from assessed species, and less than 1% of species have been assessed (Costello et al, 2012). The severity of this problem has been gradually realized, and increasing alternative methods for data-poor fisheries have been building in recent years (Dick and Maccall, 2011; Martell and Froese, 2013; Cadrin and Dickey-Collas, 2015; Hordyk et al, 2015; Froese et al, 2018)

Objectives

Methods

Conclusion