Abstract ▼ AI-Helper

Commercial catch of walleye pollock (Gadus chalcogrammus) in South Korean waters has been recorded since the mid 20th century. Based on the availability of fisheries, we could identify three developing stages of fishery over the last 5 decades: the beginning stage of fisheries (Period 1: 1958-1968),...

Commercial catch of walleye pollock (Gadus chalcogrammus) in South Korean waters has been recorded since the mid 20th century. Based on the availability of fisheries, we could identify three developing stages of fishery over the last 5 decades: the beginning stage of fisheries (Period 1: 1958-1968), peak fishing Period (Period 2: 1973-1985) and after peak fishing (Period 3: 1991-2002). To investigate the recruitment variability, we examined the length frequency of pollock caught from commercial fisheries, and the properties of habitat environment. A significant difference in length frequency distribution was found within study period. Relative length frequency indicated that the large-sized old pollock (>40 cm) as well as the immatures were obviously abundant in Period 1, while the high proportions of middle size pollock (37-43 cm) were common in Period 2 and Period 3, and length range became narrower in Period 3 than Period 2. Assuming the first maturity at 25cm and the 50% maturity at 37cm, the Proportional Size Distribution (PSD) was estimated. PSD in Period 2 (mean=60) was lower than Period 3　(mean=71). Recruitment variability seemed to be stable in Period 2, because it is usually interpreted that the PSD range of 30-70 indicates the stable recruitment. The annual PSDs also showed the opposite trend with the abundance at age-2 and age-3 estimated from the Cohort analysis. The Cross-Correlation Function analysis showed that there was a significant positive correlation between juvenile walleye pollock catch and zooplankton biomass in June with a time lag of 3 years (r=0.549, p<0.05). Furthermore, there were significant positive correlations between juvenile pollock catch and December seawater temperatures at 10 m and 20 m with a time lag of 3 years (r = 0.515 for 10 m, and 0.507 for 20 m, p<0.05), and with December seawater temperatures at 50 m and 75 m with a time lag of 2 years (r = 0.659 for 50 m, and 0.592 for 75 m, p<0.05). Age-2 abundance estimated from the Cohort analysis was positively correlated with April seawater temperature at 75m with a time lag of 2 years (r = 0.671, p<0.05). These results imply that biotic as well as abiotic environmental factors during the early life stages of pollock have a significant influence on the variability in walleye pollock recruitment.