The frequency of cetacean strandings is increasing, with multiple causes identified. We examined temporal and spatial trends in stranding numbers along the coastal areas of the East China Sea from 1990 to 2021. Using structural equation models, we analyzed the relationships between strandings and climate, oceanic properties, and human activities. Our findings revealed time-dependent interannual variability in strandings but no linear trend, indicating relative stability in cetacean strandings. Seasonal patterns were observed only in narrow-ridged finless porpoises (Neophocaena asiaeorientalis), with significant spring increases (March to May). Clustering of strandings occurred in central Fujian and northern/southern Taiwan, according to spatial analysis. The impact of variables on cetacean strandings varied across time periods. Storm surges, coastal fishing, and the Pacific decadal oscillation were associated with stranding events from 1990 to 2006. However, from 2006 to 2021, the influence of storm surges weakened, while the climate index only indirectly affected strandings through sea surface temperature and salinity, with an increased intensity in the effects of winter sea surface temperature and salinity. Structural equation models unveiled the cascading effects of environmental changes on strandings. This study reports changing trends in cetacean strandings and identifies relevant variables. Although not exhaustive, understanding the reasons behind strandings enhances our comprehension of cetacean responses to environmental changes, supporting targeted conservation and management efforts.

Accurately modeling the distribution of keystone species is of utmost importance to gain a comprehensive understanding of their complex ecological dynamics and to develop effective strategies for sustainable scientific management. In the coastal China ecosystem, the swordtip squid (Uroteuthis edulis) stands out as a keystone species with significant commercial and ecological value. Despite its importance, research on the ecological dynamics of this species remains limited and requires further investigation. To investigate the spatial and temporal variability in the distribution of U. edulis and identify the key environmental drivers in the East China Sea (ECS) and southern Yellow Sea across different seasons, we generated ensemble models using oceanographic variables and fishery-independent scientific survey data collected from 2016 to 2018. Our results revealed that U. edulis predominantly inhabited the central and southern regions of the ECS throughout the year. The primary environmental variables driving its distribution varied by season, with the sea surface temperature being the most important in spring, sea surface height in summer and autumn, and depth in winter. During summer and autumn, the suitable habitats of U. edulis were found to be largest and extended northwards towards the coastline. However, they migrated southwards to the waters near the edge of the ECS continental shelf with smaller suitable areas in the spring and winter. These results suggested that U. edulis exhibited season-specific habitat preferences and responded to changing environmental conditions throughout the year. The observed seasonal distribution patterns were likely influenced by the fluctuating mixture of waters (ocean currents) from different sources, with varying physical and chemical characteristics throughout the year. Our study provides baseline data for comprehending the population dynamics of U. edulis and highlights the significance of considering species’ habitat preferences in a dynamic environment.

Nursery habitats play a significant role in completing fish life cycles, and they are now recognized as essential habitats. Monthly variations in nursery ground distributions of Larimichthys polyactis were investigated in the southern Yellow Sea in 2019. Bayesian hierarchical models with integrated nested Laplace approximation were utilized to model the preferential nursery habitats of L. polyactis larvae. The study analyzed the spatial and temporal distributions of the larvae and juveniles based on three environmental variables: sea surface temperature, sea surface salinity, and depth. Additionally, this study examined the utilization of habitats by different fish life stages and ontogenetic shifts. A total of 3240 individuals were collected from April to June, with the peak occurring in May (0.05 ind./m³), and the distribution areas varied between different months. The prediction of the model reveals the ecological adaptability of L. polyactis to temperature variations. The optimal temperature for L. polyactis density ranges from 12.5 °C to 16.5 °C in April and 16.5 °C to 17.5 °C in May, demonstrating a broad temperature tolerance for L. polyactis survival. In addition, there are variations in distribution patterns among different developmental stages. Larimichthys polyactis spawn in the inshore and nearshore waters, and after hatching, larvae in the pre-flexion stage tend to remain aggregated near the spawning beds. However, larvae in the advanced development stage (post-flexion) and juveniles move towards the sandy ridge habitats along the coast and start to migrate offshore in June. This study provides valuable insights for the effective management of fishery resources in the area and can be utilized to identify marine areas with specific habitat features that require conservation.

Trichiurus japonicus is an economically important fish that ranks 11th in global marine fish capture production. However, the reproductive characteristics of this fish have undergone notable changes in recent decades, potentially affecting the quality of offspring and sustainable utilization. To improve our understanding of the physiological regulation of maturation in T. japonicus, untargeted liquid chromatography mass spectrometry was utilized to identify the small molecules that characterize the comprehensive metabolic profiles of ovaries during ovary development from stage II to stage IV. According to the results of OPLS-DA, the ovarian metabolite profiles of the three developmental stages were separated. The concentrations of 124 and 100 metabolites were significantly altered between stage II vs. III and III vs. IV, respectively. Lipids and lipid-like molecules accounted for the largest proportion of the altered metabolites, followed by amino acids, peptides, and analogues. The significantly altered metabolites-enriched pathways differed slightly between stages II and III and stages III and IV. Steroid-related pathways were heavily affected during stages II to III, while significantly altered metabolites from stages III to IV were involved in oocyte-maturation-related pathways. Through metabonomics analysis, potentially important metabolic pathways and metabolites between different ovarian stages were detected, providing basic information for further investigation of maturation mechanisms in wild fish.

In order to understand the diel vertical migration and transport pattern during their early life stages, the vertical distribution of larvae and juveniles of the small yellow croaker (Larimichthys polyactis) in the Yangtze River estuary was investigated. Four sampling cycles were carried out at the station (122°39′ E, 31° N) during May and June 2015. The samples were collected by vertically discrete plankton hauls in three strata of the water column: surface (0~2 m depth), middle (8~10 m depth), and bottom (18~20 m depth). The total number of small yellow croaker larvae was 5523, of which 65.2% and 25.8% were postflexion larvae and juveniles, respectively. Most of the individuals were collected in mid-May, and the sum of the quantity in May accounted for 94.8%. In all cruises, the highest abundance occurred at the bottom, while the surface maintained the lowest abundance. The flexion larvae, postflexion larvae and juveniles moved up to the surface and middle at night, but there was no significant difference between night and daytime for preflexion larvae in each stratum. The postflexion larvae and juveniles showed low temperature responses and a preference for the bottom habitat, respectively, while the preflexion and flexion larvae had weaker selectivity to the water layer and occurrence time. The abundance of larvae and juveniles in the middle layer was significantly higher at flood tide than at ebb tide, and it was more dominant at night than during the day. The study indicates that larvae and juveniles of the small yellow croaker change their located depth with diel vertical migration and utilize the faster speed of the mid-upper layer, which contributes to their ingress into the Yangtze River estuary nursery ground.