Shuhao Liu

The enoploteuthid squid species Abralia multihamata plays an important role in the epi- and mesopelagic food web. However, little is known about its seasonal and spatial distribution, life history traits, and environmental threats that may affect it. In this study, we used independent scientific bottom trawling surveys conducted in the southern Yellow and East China Seas during 2018–2019 to identify the seasonal spatial distribution characteristics of biomass, number, and size of this species as well as the relationships among these features and measured environmental factors. We also predicted the habitat distribution variations of the species under different climate scenarios (the present, SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5) and seasons. The results revealed a continuously increasing individual size from the southern Yellow Sea to the East China Sea in spring, summer, and autumn, which suggests the possibility of growth differences in different water temperature conditions. The seasonal order of regional mean biomass and number was autumn > spring > summer and winter in the study area, and, for size, it was spring > summer and autumn > winter. This result shows that the majorities of recruitment and breeding groups occurred in autumn and spring, respectively. In addition, our results showed that the most beneficial case in terms of average habitat area was SSP3–7.0 in 2050, and the most loss occurred under SSP1–2.6 and SSP5–8.5 in 2100. Few benefits were predicted for the other cases under the various climate scenarios. This study provides a new understanding of the distribution and life history of A. multihamata 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 Sepiella maindroni de Rochebrune (Hoyle, 1886) and Sepia kobiensis (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 S. maindroni 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 S. kobiensis 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 S. maindroni 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 S. kobiensis 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.