Yield-per-Recruit, Utility-per-Recruit, and Relative Biomass of 21 Exploited Fish Species in China's Coastal Seas

Lu Zhai,Daniel Pauly

doi:10.3389/fmars.2019.00724

Abstract

Based on growth and related fishery parameters, three approaches, yield-per-recruit(Y/R), utility-per-recruit (U/R) analyses and relative biomass (B/B0) analyses were applied to 21 economically important, trawl-caught species in China’s coastal seas to estimate their relative yield, economic value and biomass under different schedules of fishing mortality and mean length at first capture. The results show that all species suffer from overfishing, given the high average fishing mortality (F~1 year-1) and small mesh size (~1 cm) used by trawlers. Long-term Y/R would double and U/R (expressed as price per landed weight) would increase 5-fold if mesh size were increased to about 10 cm. Comparing Y/R and U/R showed that the benefits of higher prices for larger individuals were detectable only if larger mesh sizes are used, so that individuals are caught only after they have been able to grow. The Y/R analyses also allowed estimating the biomass of the 21 assessed populations relative to their unexploited biomass, i.e., B/B0. Species-specific B/B0 values ranged from 0.01 to 0.58, with a mean of 0.16 (+/- 0.03), i.e., much lower than the 50% reduction corresponding to Maximum Sustainable Yield (i.e., B/BMSY =1), or B/B0 =0.5). This confirms the many authors who reported systematic overfishing along China’s coastlines, and suggests that rebuilding stocks should be the foremost goal of fisheries management in China.

Highlights

According to statistics of the Food and Agriculture Organization of the United Nations (FAO, 2016), the People’s Republic of China, was the top-ranking fishing country in the world with domestic marine catches of about 10 million t in the 2010s.As part of its Thirteenth Five-Year Plan (2016–2020), China listed the need for improvement of its fishery management systems
The estimated mean size at first capture (Lc) of 11 of 14 species were smaller than their predicted length at age zero, i.e., with the current mesh size, most of the fish are predicted to be caught as soon as they are hatched, i.e., as larvae
It has been often assumed that fisheries produce the maximum sustainable yield (MSY) when E = M/Z = 0.5, i.e., F = M

Summary

Introduction

According to statistics of the Food and Agriculture Organization of the United Nations (FAO, 2016), the People’s Republic of China (hereafter referred to as “China”), was the top-ranking fishing country in the world with domestic marine catches of about 10 million t in the 2010s (www. fao.org and www.seaaroundus.org).As part of its Thirteenth Five-Year Plan (2016–2020), China listed the need for improvement of its fishery management systems. Several policies aiming at stabilizing fisheries catches have been proposed, but their implementation has not necessarily been successful. One of the most important management measures, the “Double Control” system, was proposed in the early 1990s to regulate fisheries by controlling the number of engine-powered fishing vessels and the cumulative power of the fleet (Shen and Heino, 2014). Despite a decrease in the number of fishing vessels since 2004, cumulative fleet engine power and tonnages have increased (Anonymous, 1979–2019; Figure 1A), and CPUE and total catch continued decreases that began in 1998 (Shen and Heino, 2014; Figure 1B)

Methods

Results

Conclusion