Potential Impact of Late 1980s Regime Shift on the Collapse of Walleye Pollock Catch in the Western East/Japan Sea

Abstract

Walleye pollock (Gadus chalcogramma) caught in the Korean fishing area dramatically decreased in the late 1980s. To investigate the potential impact of the late 1980s climate regime shift on the collapse of the pollock catch, we developed a three-dimensional hydrodynamic model with data assimilation and a particle tracking model. Data-assimilated reanalysis showed that sea surface temperature increased by approximately 2°C in the spawning area of pollock in the late 1980s. The suitable spawning area in the East Korean Bay decreased due to warming in the late 1980s. Spawned eggs of walleye pollock were tracked using a particle tracking model for 30 days in January and February during 1983–1992. The number of individuals transported to the nursery within the Korean fishing area from the spawning area was reduced by 74% in the late 1980s. The intensified East Korean Warm Current (EKWC) could be responsible for the decreased number of individuals transported to the southern area in the late 1980s. Warming in the Korean fishing area could also cause a decrease in pollock. These oceanic changes might be linked to climate regime shifts in the late 1980s. The warming regime with positive Arctic Oscillation and weakened monsoon intensified the northward flow of the EKWC and accelerated the warming of the spawning and fishing areas in the late 1980s.

Severe reduction in spawning days and larval abundance of walleye pollock under future warming in the western East/Japan Sea

“…The RCM-ENS shows colder SST in the coastal EKB, where the observational error of the OISST is large (0.4) near the coastal region (figure 2(c)). A cold coastal SST pattern was also shown in a previous study using reanalysis data [14].…”

“…To simulate the transport process for the eggs and larvae, Particle tracking experiments based on ocean circulation models can be useful tools [29][30][31][32][33]. Transport processes of walleye pollock have been explored in several regions using particle tracking models [14,[34][35][36][37]. Despite several studies being undertaken, a high-resolution future simulation resolving the physical environment of western EJS region are currently unavailable.…”

“…Therefore, the Korean government is making efforts to restore walleye pollock resources in Korean fishing area. Physical environmental changes in habitats may be linked to the reduction in walleye pollock catches [12][13][14]. Specifically, after the late 1980s, a warmed regime influenced the western EJS ecosystem [14][15][16].…”

“…Physical environmental changes in habitats may be linked to the reduction in walleye pollock catches [12][13][14]. Specifically, after the late 1980s, a warmed regime influenced the western EJS ecosystem [14][15][16]. Both global warming and periodic climate variability could contribute to driving ecosystem changes.…”

Wintertime sea surface temperature variability modulated by Arctic Oscillation in the northwestern part of the East/Japan Sea and its relationship with marine heatwaves

“…Indeed, there are several physical processes that affect the SST variability in the EJS including: local wind forcing (Minobe et al, 2004;Shimada and Kawamura, 2006), East Asian monsoon (Yeh et al, 2010;Jeong et al, 2022), and the Tsushima Warm Current (TWC) transport (Kim et al, 2004). In addition, it has been reported that the spatiotemporal variability of chlorophyll-a concentration and the fish catch in the EJS is closely associated with its SST variations (Park et al, 2020;Kim et al, 2022;Park et al, 2022). In spite of a wealth of studies, it is still valuable to examine the physical mechanisms that lead to the SST variability in the EJS.…”