Changes in the abundance and distribution of walleye pollock ( Theragra chalcogramma) in the western Gulf of Alaska (1961–1984)

Changes in the abundance and recruitment of western Gulf of Alaska walleye pollock ( Theragra chalcogramma) during 1961–1984 were examined. Bottom trawl survey CPUE estimates increased between the early 1960s and early 1970s. Independent biomass estimates from acoustic surveys and catch-at-age analyses of foreign and joint venture fisheries indicate that another increase in abundance occurred during 1978–1981, but that stock size has declined since 1981 or 1982. Biomass was estimated at 950 000 metric tons (t) in 1973–1974, 2.3–3.8 million t in 1981 and 1.8 million t in 1984. The fluctuations in stock size reflect substantial changes in year-class strength. These include the occurrence of strong year classes in 1967, 1970, 1972 and 1975–1979. Weak year classes apparently occurred in 1980–1982. Based on spawner-recruit estimates since 1976, pollock recruitment may be strongly density dependent. It is believed that there has been a shift, since 1977, in the abundance of pollock from the Kodiak-Chirikof area, westward towards the Shumagin Islands.