Fluctuations in abundance of Northeast Arctic cod during the 20th century

Annual sampling of Northeast Arctic cod for age determinations during 1913-1929 was based on scales, but beginning in 1932, the sampling was based on otoliths. The Norwegian sampling programme was concentrated on landings of mature cod in the winter and of immature cod in the spring. In the late 1920s and early 1930s, age determinations of mature fish indicated a lower frequency of older fish in scale samples than in otolith samples. Misclassification of age in scale samples of immature cod was assumed to be of minor importance. To overcome the misclassification of age in mature fish, a scale-age/otolith-age "key” was applied to scale-age compositions of mature fish. These annual converted age compositions together with the scale-age compositions of immature cod for 1913-1929 were used to establish total annual catch in numbers at age by years. Similar data for 1932-1945 were based on otolithage compositions. In conjunction with similar published data for 1946-1999, a virtual population analysis was run for the entire 20th century after 1913. The historic development of total and spawning-stock biomass, fishing mortality, and recruitment at age 3 was investigated. In addition, the lognormal distribution was applied to the recruitment data for the 87 year classes that were analysed, and the Beverton and Holt and Ricker curves were fitted to the spawning-stock/recruitment data.

Article from Marine Science Symposia Vol. 215 - 100 years of science under ICES. To access the remaining articles please click on the keyword "MSS Vol. 215".