Assessment of Tropical Fish Stocks Using the LBB Method in Dongzhaigang Bay, Hainan Island, China

Abstract

This study used catch/effort (CPUE) and length-frequency (L/F) data to evaluate the status of 26 fish species in the mangroves of the Dongzhaigang National Reserve, Hainan Province, China, sampled in 2009 (16 species), 2014 (18 species) and 2020 (15 species) using CPUE and the length-based Bayesian biomass (LBB) method. The CPUE, both in number and weight, was lower in 2009 than in 2014 and lower again in 2020, with the 2009 low attributed to pollution due to shrimp, pig and duck farming within the reserve. Of the 26 fish species assessed, four experienced a large reduction of length from 2009 to 2020, and nine exhibited a decline in the ratio of current biomass to biomass at carrying capacity (B/B0), which is expressed as the ‘biomass left’. This ratio was, for most species, below 0.5 in 2009, which suggests that overfishing occurred in 2009 and that it has since become worse. Thus, while the CPUE data provided ambiguous results, the L/F data analyzed by the LBB method demonstrated unambiguously that ‘miniaturization’ through overfishing is occurring among the exploited 26 fish species from the mangroves of the Dongzhaigang National Reserve. For the fisheries in the mangals of Dongzhaigang Bay to remain viable, fishing effort should be reduced by local governments working with the affected communities, just as they reduced pollution a decade ago.