Effects of water temperature changes on the early life stages (egg and larvae) of walleye Pollock (Gadus chalcogrammus) – Laboratory experiments and field applications

The Long-Term Dynamics of Walleye Pollock Stocks in Relation to Oceanographic Changes in the East Sea

“…In Korean waters, the rate of warming in the upper layer, which serves as the primary habitat for larvae and eggs, is higher than that of the intermediate and deep layers where adult pollocks reside [47]. These changes in oceanic conditions in spawning grounds affect mortality during the early life stages [10,48,49]. Specifically, the timing of creating suitable oceanic conditions for spawning and hatching [50], advection of eggs and larvae [17,51], and food sources are important factors influencing changes in survival rates and mortality during the early life stages [4,52].…”

“…Most pollock spawn between January and March, with the eggs remaining in the surface layer after release as pelagic eggs [16,41]. The suitable temperature range for spawning grounds falls between 2-5 • C, considering the known optimal spawning temperature [21] and its correlation with low mortality [9,10,17,22,23]. Hence, changes in the spatiotemporal distribution of the spawning grounds were estimated using the following methods: (1) Assessing changes in the duration of suitable temperature (2-5 • C) for spawning (DTS) and its horizontal distribution at each decade using daily SST data, and (2) Analyzing long-term changes in the regional proportion for suitable spawning conditions (2-5 • C) (RPS) relative to the total area of DB.…”

“…However, pollock production in Japan and Russia has either remained stable or slightly increased after 2000 [8], while the pollock catch in the United States and Canada, situated in the North Pacific, has not continued to decline since 2000 but has instead maintained a stable level [8]. In Korean waters, pollock fisheries have also undergone a drastic decline since the late 1980s, with catches plummeting below 1000 tons, nearly reaching extinction since 2000, in contrast to production in other countries [7][8][9][10][11].…”

“…(2) ocean warming in their habitat grounds [7,9,10]; and (3) food availability impacting growth, survival, and recruitment [31,32]. However, these hypotheses are primarily based on simple correlation analyses of individual parameters affecting changes in total pollock catch, such as water temperature and zooplankton biomass [29].…”

“…Additionally, these hypotheses lack ecological information, such as size and sex composition, for each period. To gain a more comprehensive understanding of the drivers behind changes in fishery resource biomass, it is imperative to consider varying responses to oceanic conditions and overfishing at each life stage and their corresponding mechanisms [7,10,30].…”