Using 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.

中文翻译：

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基于底拖网调查数据的北部湾平均营养层年代际尺度变化

利用海底拖网调查数据检查南海北部湾的渔业资源，对种群密度，优势物种组成，平均营养水平和捕捞不平衡指数的变化进行了综合分析。结果表明，从1961年到2017年，海湾地区渔业资源的种群密度下降。从北部湾进行的拖网调查中优势物种的组成在1961–1962年至2016–2017年间发生了巨大变化，并显示了从底层物种向中上层物种的转变从高营养水平种到低营养水平种。低营养水平物种的捕获量增加，而高营养水平物种的优势下降。海湾鱼类的平均营养水平从1961-1962年的3.90下降到1998-1999年的3.45，每十年的营养水平为0.13，然后开始增加到3。在2016-2017年期间，这一数字为65，每十年的营养水平为0.12。捕捞平衡指数在1998–1999年下降至–0.96，然后略有上升。结果表明，北部湾的渔业资源已被过度捕捞。因此，我们建议降低捕捞压力并加强执行保护措施，例如暂停夏季捕捞，加强捕捞和建造人工鱼礁。