Decadal‐Scale Variation in Mean Trophic Level in Beibu Gulf Based on Bottom‐Trawl Survey Data

Abstract

AbstractUsing bottom‐trawl survey data to examine fishery resources in the Beibu Gulf, South China Sea, changes in stock density, dominant species composition, mean trophic level, and the fishing‐in‐balance index were comprehensively analyzed. The results show that the stock density of fishery resources declined in the gulf from 1961 to 2017. The composition of dominant species in trawl surveys from Beibu Gulf changed greatly from 1961–1962 to 2016–2017 and showed a shift from bottom species to pelagic species and from high‐trophic‐level species to low‐trophic‐level species. Catches of low‐trophic‐level species increased, while the dominance of high‐trophic‐level species declined. The mean trophic level of fish from the gulf declined from 3.90 in 1961–1962 to 3.45 in 1998–1999 at a rate of 0.13 of a trophic level per decade and then began to increase to 3.65 in 2016–2017 at a rate of 0.12 of a trophic level per decade. The fishing‐in‐balance index dropped to –0.96 in 1998–1999 and then slightly increased. The results indicate that fisheries resources in the Beibu Gulf have been overfished. Therefore, we recommend reducing fishing pressure and strengthening the implementation of protection measures, such as summer fishing moratoriums, enhancement, and artificial reef construction.