Bottom longline fishing of red tilefish (Branchiostegus japonicus) is one of the most important commercial of fishing in the East China Sea. The present study aimed to investigate hook selectivity in B. japonicus and D. tumifrons, by means of experiments using three hook sizes (“J”: #15, #13 and #11) and was conducted in the East China Sea from June to August 2018. Altogether 602 B. japonicus fish and 858 D. tumifrons fish were caught. With respect to the size of the hook used, the total length-frequency varied significantly for both B. japonicus and D. tumifrons that were caught. The total length and four mouth parameters (upper and lower jaw length as well as height and width of mouth opening) of the two species showed a positive linear relationship. A logistic model created using the maximum likelihood method was used for elucidating hook selectivity; the best fit model with the minimum Akaike’s Information Criterion value was selected as the final model. The 50% selection lengths were 224.827 and 233.179 mm for B. japonicus; 201.461 and 202.603 mm for D. tumifrons using “J” #13 and “J” #11 hooks, respectively. To preserve the reproductive potential of younger fish in the stocks, the size of the “J” #13 hook was selected as the minimum hook size that should be used for the sustainable development of bottom longline fishing for B. japonicus and D. tumifrons.

This study systematically evaluated the dynamic habitat suitability of Portunus trituberculatus in the East China Sea and the Yellow Sea region (referred to herein as the East Yellow Sea region for brevity) under climate change impacts by integrating a species distribution model (Biomod2) with multi-source environmental data. Through the construction and evaluation of an ensemble model combining 10 algorithms, using the Area Under the Curve (AUC) and True Skill Statistic (TSS) for validation, we identified seabed temperature, seabed salinity, and chlorophyll as key environmental factors. Results showed that current high-suitability areas are concentrated in coastal Jiangsu, the Yangtze River estuary, and Zhoushan Archipelago waters, which overlap significantly with fishing hotspots. Under future climate scenarios, the species’ suitable habitat distribution is projected to shift significantly poleward: In the SSP5-8.5 scenario 2100, low/medium suitability areas increased by 38.2% and 88.2% respectively, while high-suitability areas decreased by 36.5%, with core spawning grounds (e.g., Zhoushan Archipelago waters) showing reduced suitability indices. The Bohai Sea’s summer water temperature unsuitability for Portunus trituberculatus migration creates an “ecological bottleneck” for northward expansion. The study proposes strengthening habitat management in Jiangsu coastal areas and integrating dynamic habitat prediction into fisheries policies to address climate-induced resource redistribution and ecosystem service changes. Our findings underscore the urgency of incorporating climate-driven habitat shifts into adaptive marine spatial planning and fisheries management frameworks.

To investigate the spatiotemporal distribution and causes of blooms of Rhopilema esculentum in Hangzhou Bay during 2024, this study investigated its growth characteristics, including umbrella diameter and body weight, along with environmental factors, spatiotemporal dynamics and yield variations. The analysis was based on the 2024 monitoring data of R. esculentum resources in Hangzhou Bay, together with relevant social research data. The results showed that umbrella diameter and body weight increased over time at all monitoring points. The growth rate of the R. esculentum umbrella diameter declined gradually over time, whereas that of body weight rapidly increased. The daily growth rate of umbrella diameter in the water of Tangnao and Xiaoji Mountains was significantly higher than that in the waters of Tanxu Mountain. A sharp drop in salinity caused by Xin’anjiang Reservoir flood discharge from the 23rd to 28th June was the primary cause of the R. esculentum blooms in Hangzhou Bay. During the special R. esculentum fishing period in the summer fishing moratorium, R. esculentum was mainly distributed in the southern and eastern Hangzhou waters, with a maximum daily yield of 28,000 kg/day. After the 16th, R. esculentum production expanded across the entire bay, with blooms also occurring in Xiangshan Bay and Liuheng, reaching a production peak of 44,000 kg/day. In 2024, R. esculentum production in Hangzhou Bay totalled 250,000 tonnes, breaking historical records. This study revealed the 2024 growth and spatiotemporal dynamics of R. esculentum in Hangzhou Bay, providing a reference for the rational use and protection of the species and revealing the causes of the unprecedented blooms.