Feeding conditions of north-east Arctic (Arcto-Norwegian) cod larvae compared to the Rothschild-Osborn theory on small-scale turbulence and plankton contact rates

Abstract

Data on first feeding North-east arctic cod larvae in Lofoten, sampled during the period 1976 - 1984, are examined to verify the theory on the influence of microturbulence on the contact rate between predator and prey (Rothschild and Osborn, 1988). The number of prey per gut of the cod larvae are compared to the concentration of prey, Calanus finmarchicus nauplii, and to data on wind speed and static stability of the upper layer. The data indicate that the contact rate increases by 2. 8 when the average wind speed increases from 2 m s -1 to 6 m s -1 . Independent data on cod larval cruising speed, the velocity and concentration of prey organisms, inserted into the model of Rothschild and Osborn (1988) show a comparable increase of the contact rate of 2.2 for the same increase of wind speed. Larval stages of North-east arctic cod are important for the formation of the year class. Larval stages are confined to the mixed layer, and therefore the variable contact rate induced by wind mixing is an important regulatory mechanism for the formation of year class strength.