An abundance estimate of ling ( Molva molva) and cod ( Gadus morhua) in the Skagerrak and the northeastern North Sea, 1872

Abstract

Fisheries management may suffer from historical myopia, because most stock assessments are based on time series which are ca. 30–40 years long. This investigation examines changes in population dynamics of two gadoid species in the Skagerrak- northeastern North Sea on a century scale, and argues that long-term, historical abundance estimates are relevant to the determination of biomass reference points in fisheries management. Situated within the field of historical ecology, this paper presents findings on the abundance of ling and cod in 1872. Calculations are based on historical CPUE and catch data. Ling abundance was ca. 100–200 million individuals aged 4+ and probably exceeded cod abundances (ca. 3 million individuals aged 3+) in the Skagerrak and in the northeastern North Sea in 1872. Current ling abundances are unknown but probably lower than in 1872, as reflected in declining landings during the late 1990s–early 2000s. Dominating ling size has also declined since the late 19th century. The estimated historic abundance of cod in the Skagerrak and northeastern North Sea is similar to present abundance of cod in these areas but its spatial distribution has contracted. These changes in the ling and cod populations are consistent with effects of fishing on populations and should be considered when setting fishery management plans for population recovery and sustainability.