Natural mortality, stock–recruitment relationship and sustainable yield of the anchovy (Engraulis japonicus) stock in the Yellow Sea were estimated based on acoustic assessments of the wintering anchovy stock from 1987 to 2002. The stock‐recruitment relationship was estimated to be: R = 151.1 × SSB × e−0.299·SSB, where R is given in billion fish and SSB is in million tons. The optimum sustainable yield of anchovy was estimated at 520 000 tons for the period 1987–2002. The ecological consequences of the sharp decline of the anchovy stock observed after 1996 were examined in terms of the reduction in biomass production in the Yellow Sea ecosystem, as well as the consequences of such reduction on predator–prey interactions and species competition.
Detecting and analyzing patterns of distribution shifts and range expansion/contraction is important to understand population dynamics and changes in stock status. Here, we develop a spatio-temporal model for yellow croaker (Larimichthys polyactis), which was fitted to bottom trawl survey biomass data collected in the Yellow Sea in the winter of 2001-2017. The model accounts for both spatial and spatio-temporal structure and can potentially include the effects of surface temperature and of an annual index, the Pacific Decadal Oscillation, represented using a recently developed spatially varying coefficient model. We selected a spatio-temporal model with no covariates based on Akaike's information criterion. The center of gravity for yellow croaker was found to move northwest between 2001 and 2010, and then southwest over the period 2010-2017. These results reflected the predicted progressive disappearance of yellow croaker density hotspots (i.e., highest density areas) in the north and southeast areas of the Yellow Sea, which resulted in the central area of the Yellow Sea becoming the only yellow croaker density hotspot in 2017. This finding has important implications for fisheries management in the context of the China-South Korea fisheries agreement, as it indicates a measurable displacement of yellow croaker biomass toward China. The exclusion of covariates from the spatio-temporal model was not expected a priori and may be due to the facts that environmental
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