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Based on fishery resources and environmental data collected during six cruises conducted in the spring and autumn from 2021 to 2023 in the northern Beibu Gulf, South China Sea, we conducted an analysis on spatiotemporal distribution of crimson seabream (Paerargyrops edita). We employed a gradient forest analysis (GFA) and generalized additive model (GAM) to investigate the relationship between their distribution and six environmental factors, including sea surface temperature (SST), sea surface salinity (SSS), sea surface chlorophyll a concentration (Chla), bathymetry (Depth), sea surface height (SSH), as well as the Niño 3.4 index (NI). The results revealed distinct spatiotemporal variations in the distribution of crimson seabream in the northern Beibu Gulf, with an average stock density of 114.21 kg/km2. During spring, there was a significantly higher abundance at 160.46 kg/km2 compared to the autumn value of 67.95 kg/km2. In the first analysis, based on 1000 runs of the GFA, it was observed that the selected explanatory variables demonstrated excellent predictive capabilities for variations in stock density. Specifically, the SST, SSS, and NI were found to have a high importance, indicating a significant influence of climate and environmental factors such as the El Niño-Southern Oscillation (ENSO) and SST on the crimson seabream abundance. Subsequently, we constructed a GAM to further investigate the impact of environmental factors on the distribution patterns of crimson seabream. The GAM also confirmed a strong correlation between the selected environmental factors and crimson seabream abundance. The main distribution of crimson seabream abundance exhibited a significant negative correlation with the SST, which fell within the range of 24–28 °C. The stock density of crimson seabream slightly increased at SSS levels ranging from 32.5 PSU to 33.5 PSU, indicating a correlation between the two factors. The crimson seabream was distributed across a Chla range of 0–4 mg/m3, with a gradual increase in stock density as the Chla levels increased. Stock density was positively correlated with SSH, but was negatively correlated with NI. In this study, we examined the distribution of crimson seabream and its main influencing factors by incorporating various environmental factors and a network analysis under different climate events. This research provides theoretical support for investigating the mechanisms of fishery stock in response to climate change. It also contributes to the existing body of knowledge on changes in fish resources in Beibu Gulf during abnormal climate events.

Marine ecosystems are a primary conservation concern because of the separate and synergistic effects of overfishing and climate change on their productivity and biodiversity. For the purpose of implementing ecosystem-based fisheries management, it is essential to understand how fish stocks respond to climate change in marine ecosystems, especially those that have been overexploited. The Beibu Gulf in the northwestern part of the South China Sea has long been one of China’s major fishing grounds. After the collapse of the demersal ecosystem in 1990 s, small pelagic fishes, including Japanese jack mackerel (Trachurus japonicus) and Japanese scad (Decapterus maruadsi), have occupied a more-important ecological niche in this gulf. However, insufficient research on how small pelagic fish respond to climate change creates great uncertainty for implementing the current management measures. This study used fish data of trawl surveys and environmental data to investigate possible mechanisms leading to dramatic fluctuations in small pelagic fish populations and their possible effects on the Beibu Gulf marine ecosystem. Abnormal blooms of small pelagic fish, especially T. japonicus and D. maruadsi, occurred following four La Niña events (in 2007/2008, 2010/2011, 2011/2012, and 2020/2021). Moreover, the dominant fish species shifted observably and regularly, Shannon–Wiener diversity and Pielou’s evenness decreased significantly in the northeastern coastal waters of the gulf, and the spatial pattern of the fish community was reorganized in this ecosystem. The small pelagic fish blooms in summers probably resulted from a combination of climate change, overfishing, and a summer fishing moratorium, which thereby caused a series of responses in the marine ecosystem. Fluctuations in the small pelagic fish populations after La Niña events seemed more dramatic after the collapse of demersal fish stocks. Therefore, we emphasize the need for implementing ecosystem-based, preventive, and adaptive fisheries management.