Changes in the Biological Characteristics of Walleye Pollock Related to Demographic Changes in the East Sea During the Late 20th Century

Abstract

Walleye pollock Gadus chalcogrammus (hereafter, pollock) was one of the predominant fish species in Korean waters during the 1970s and 1980s, but catches decreased rapidly beginning in the late 1980s and the fishery collapsed in the 2000s. The biological characteristics of fish species tend to depend on their biomass and environmental conditions. To investigate the changes in the biological characteristics of pollock (such as their size frequency, condition factor, and maturation) associated with biomass levels as well as the possible causes of the stock collapse as a result of environmental changes, we used data collected by the Korean National Institute of Fisheries Science (NIFS) during high (1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985) and low (1991-2000) periods of pollock biomass. Density-dependent effects on the pollock population were evident in Korean waters: pollock were larger and heavier at length during the low-biomass period. The gonadosomatic index also indicated that the peak spawning season was broad (from October to February) during the high-biomass period and narrower (December and January) during the low-biomass period. The population abundance and recruitment success of Korean pollock appear to have been affected by the warming of the ocean surface from the early 1990s. Thus, we suggest that the biomass fluctuations associated with environmental changes during their early life stages were responsible for the observed changes in the biological properties of pollock.

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

“…The Korean government initially prohibited the fishing of juvenile pollock but lifted this prohibition after 1974, which led to the continuation of juvenile pollock fishing until the early 1990s [64,65]. During the mid-1970s, juveniles constituted over 80% of the total catch, and this high proportion of juvenile catches persisted until the mid-1980s [18]. The high intensity of juvenile fishing appears to have been influenced by both biological characteristics and advancements in fishing techniques and gear.…”

“…This continued fishing for juvenile pollock for over a decade has likely contributed to overfishing [64]. The ongoing and increased fishing pressure on juvenile pollock has had an impact on adult pollock biomass and recruitment [18]. The highest recorded catch of juvenile pollock was in 1981, with a significant decline in the total catch of juvenile pollock after 1984-1985.…”

“…Donghan Bay (DB) in North Korea is the primary spawning ground for pollock in Korean waters [11,18]. Pollock aggregate to spawn during winter, from January to March, and the eggs released during this period remain in the surface layer [19,20].…”

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

“…The East Korea Bay (EKB) off the coast of Korea is known as a major spawning ground for walleye pollock in the EJS (figure 1) [8][9][10], and the species living in the Korean fishing area spawn in the bay [10,11]. In contrast to the stable catches in Japan and Russia, the catch in Korea has significantly declined since the 2000s and has not yet fully recovered [4,9]. Due to the importance of walleye pollock in commercial fisheries, the decline in pollock stocks has posed a critical challenge in managing Korean fisheries.…”

Draft Assembled Genome of Walleye Pollock (Gadus chalcogrammus)

“…The country also focuses on species that are not adapted to artificial aquaculture systems. In this study, we sequenced the genome of Gadus chalcogrammus (walleye pollock), a cold-water species with a deep-sea habitat (200-1,200 m depth) that requires temperatures of 1-10 • C to survive (Bang et al, 2018). It is the second most commonly consumed fish in Korea, and is used worldwide in foods, such as surimi and roe (Anvari et al, 2018).…”