Seasonal Analysis of Spatial Distribution Patterns and Characteristics of Sepiella maindroni and Sepia kobiensis in the East China Sea Region

Climate change is having important effects on the migration routes and seasonal-spatial distribution patterns of aquatic animals, including the cephalopods <i>Sepiella maindroni</i> de Rochebrune (Hoyle, 1886) and <i>Sepia kobiensis</i> (Hoyle, 1885) in the East China Sea region. We conducted bottom trawling surveys from 2018 to 2019 in the East China Sea region to identify the seasonal-spatial distribution patterns, including the locations of spawning and nursery grounds of both species, and to determine how they are related to environmental variables. We used random forests and boosted regression trees to identify the distribution patterns of both species from spring to winter to estimate the annual mean situations. We also predicted the habitat distribution variations in 2050 and 2100 under the SSP1-2.6 and SSP5-8.5 climate change scenarios. From our survey data, we detected increasing biomass densities of <i>S. maindroni</i> from 29.50° N to 28.50° N, where the largest value of 213.92 g·ind^-1 occurred. In spring, juvenile groups were present in coastal areas and larger individuals were found in offshore areas. We identified potential spawning grounds at 29.50°-33.00° N 122.50°-123.00° E adjacent to the Zhejiang coastline, and larger individuals and higher biomass densities in south of the 29.50° N line in summer. In autumn, the average individual weight increased in the 28.00° N 122.00° E→124.00° E area. We located potential <i>S. kobiensis</i> spawning grounds at 27.00° N 122.00°-123.50° E in spring. Growing overwintering juveniles migrated to the area of 29.50°-30.50° N 125.00°-127.00° E in winter. The sea surface temperature of the areas inhabited by both species showed obvious seasonal variation. The SSP1-2.6 and SSP5-8.5 scenarios indicated that the habitat of <i>S. maindroni</i> would shift to the south first and then to the north of the study area with the intensification of CO₂ emissions, and it would first expand and then greatly decrease. However, the habitat area of <i>S. kobiensis</i> would increase. Our results will contribute to a better understanding of the life history traits of both species and the changes in their distribution patterns under different climate scenarios to ensure sustainable exploitation and fisheries management.