Changes in Distribution Patterns for Larimichthys polyactis in Response to Multiple Pressures in the Bohai Sea Over the Past Four Decades

Abstract

Understanding patterns of change in the distribution of species among their critical habitats is important for analyzing population dynamics and adaptive responses to environmental shifts. We investigated spatio-temporal changes in small yellow croaker (Larimichthys polyactis) using eight alternative models fitted to data from bottom trawl surveys conducted in the Bohai Sea each spring (spawning period) and summer during 1982–2018. These models included different combinations of local sea temperature, fishing pressure, and individual climate index (i.e., North Pacific index, NPI, and West Pacific index, WPI) as explanatory variables. Selection of the most parsimonious model for each season was based on Akaike’s Information Criterion (AIC). The model with NPI as its only explanatory variable was used as a base case for pre-analysis. In spring, a spatio-temporal model with sea temperature as a quadratic effect, plus the spatially varying effects of a climate index and fishing pressure was selected, as the AIC value of this model was reduced by 41.491 compared to the base case model without these effects. In the summer after spawning, the spatio-temporal model with WPI as a climate index covariate lagged by 1-year best explained the spatio-temporal distribution patterns of the stock. The results suggested that small yellow croaker populations significantly decreased in biomass in the Bohai Sea over the study period. A statistically significant northeastward shift in the center of gravity (COG) and a contraction in the distribution range occurred in summer throughout the study period (p<0.05). During the spring sequence (1993–2018), a statistically significant northeastward shift in the COG was also found (p<0.05). Our results showed that biomass-density hotspots of small yellow croaker in both seasons have shrunk or disappeared in recent years. Overall, these findings suggest that the spatio-temporal patterns of the populations in their spawning, feeding and nursery grounds have been influenced over the past 40 years by multiple pressures, and population density in the southwestern areas of the Bohai Sea declined faster and more drastically than in the northeastern areas. This study has important implications for developing targeted spatial conservation measures for small yellow croaker at various stages of its life history under different levels of stress.

Exploring reconfiguration of trends in CPUE to model sustainable TAC options for the pivotal YSLME anchovy fishery

“…The time series are shown in Figure 2. Fishing vessel power data provides the only long time series effort data available in China and is widely used or considered in Chinese fisheries research (e.g., Liu et al, 1990;Lin et al, 2016;Liu et al, 2017;Han et al, 2021;Han et al, 2022). However, these data do not capture advances in the development of fishing technology, vessels and gear.…”

“…In China, the representativeness of nominal CPUE as a proxy for stock biomass has also been doubtful. This is because total vessel power does not account for technological advances, and so has proven to be a poor indicator of fishing mortality (Han et al, 2021;Han et al, 2022). For the YSLME anchovy fishery, total vessel power existed as a measure of effort long before the present technology was developed and matured, and so does not reflect the true changes in fishing effort and efficiency due to the time course of technology diffusion and adoption of further advances in fishing operations.…”

Long-term changes in the spatio-temporal distribution of snailfish Liparis tanakae in the Yellow Sea under fishing and environmental changes

“…Following the implementation of a double control system on fishing vessels in China, the number of fishing vessels decreased and the rate of increase in total horsepower reduced. However, the rate of increase in fishing pressure had greater impact despite the reduced rate of increase in total horsepower due to technological innovation and increased fishing efficiency (Han et al, 2022). In view of this, we chose the highest power group to represent the strength of FP, which was calculated by summing the total horsepower of active fishing vessels above 441 kW, including those from Shandong, Jiangsu, Hebei, and Liaoning Provinces, and Tianjin City recorded in the China fishery statistical yearbooks (MARA, 2003(MARA, -2020.…”