Bogstad, Bjarte

Helle, Kristin

Ottersen, Geir

NORA - Norwegian Open Research Archives

CM 2001/ V:21  Not to be cited without prior reference to the authors   Current patterns during pelagic stages determine interannual variability  in length-at-age of juvenile Arcto-Norwegian cod  by Geir Ottersen1, Kristin Helle, and Bjarte Bogstad Institute of Marine Research, P.O. Box 1870 Nordnes, N-5817 Bergen, Norway.   ABSTRACT2 The large Arcto-Norwegian stock of cod (Gadus morhua L.) in the Barents Sea exhibits a pattern of pronounced year-to-year variability in individual growth. Earlier authors have suggested both density-dependent and density-independent causes. Here three hypotheses for the observed close inverse relation between abundance and length-at-age of juveniles (1-4 year old fish) are suggested and evaluated: I) Population size, high abundance leading to reduced growth (density-dependent growth). II) Population size, through altering geographical distribution pattern and thus ambient temperature. III) Abiotic, density-independent mechanisms during the pelagic stages. Enhanced inflow of warm, prey-rich Atlantic water masses from the southwest leads to an abundant cohort as 0-group distributed farther east into colder water masses, which causes lower post-settlement growth rates. Based on comprehensive data, we conclude that year-to-year differences in juvenile length-at-age mainly are a consequence of distribution patterns determined during the pelagic first half year of the fishes’ life (hypothesis III). We can not reject density-dependent growth effects directly related to variability in food rations (I), but our data do not suggest this to be the main mechanism. II) is rejected, mainly due to year-to-year differences in length being established already at age 2, which is too early for such movements.                                                   1 Current address: University of Oslo, Dep. Biology, Div. Zoology, P.O. Box 1050 Blindern, N-0316 Oslo, Norway 2 The full paper this presentation is based on will appear in Canadian Journal of Fisheries and Aquatic Sciences. 

Current patterns during pelagic stages determine interannual variability in length-at-age of juvenile Arcto-Norwegian cod

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