Covariability in early growth and year-class strength of Barents Sea cod, haddock, and herring: the environmental link

We address the hypothesis that survival of a cohort is directly related to growth rates during the pre-recruit period for marine fish. This hypothesis is widely accepted, but supporting field evidence has been elusive. Here the connection between size and year-class strength at the early stages is examined for the commercially important Barents Sea stocks of cod (Gadus morhua), haddock (Melanogrammus aeglefinus), and herring (Clupea harengus). We show that there is a close link between length and year-class strength at the 0-group stage within and among the populations studied, and that the connection also holds between length at the 0-group stage and strength of recruitment at age 3. Both length and abundance are closely related to temperature. Interannual variability in the temperature conditions is concluded to be the underlying cause of the covariability between growth and year-class strength. We hypothesize that for stocks at the high latitude end of the overall range of the species the environmental signal tends to over-ride density-dependent effects on growth. High temperature will cause a high production of prey items leading to higher growth rates and higher survival through the vulnerable larval and juvenile stages. The duration of the high-mortality and vulnerable stages is also decreased by higher temperature directly increasing the development rate. (C) 2000 International Council for the Exploration of the Sea.