Effects of anthropogenic feeding on the growth rate, nutritional status and migratory behaviour of free-ranging cod in an Icelandic fjord

Abstract

The growth rate of wild, free-ranging cod increased substantially in a 17-month feeding experiment in Stödvarfjördur, a small Icelandic fjord. The feed, mainly capelin and herring, was dispensed in the fjord from a boat three times a week, 2-10 tonnes per month. During feeding an audio signal was transmitted and the response of the fish observed with an underwater video camera. Within a few weeks thousands of cod had been conditioned to feed. To study the growth rate and migratory behaviour, 2539 cod were tagged and released in Stödvarfjördur and three control areas. All the recaptured fish tagged in the control areas had liver indices less than 10% (unconditioned fish), whereas nearly half of the recaptured fish tagged in Stödvarfjördur had liver indices greater than 10% (conditioned fish); 95% of the conditioned cod were recaptured within 5 nmi from the feeding areas. The growth rate and liver index of cod tagged in Stödvarfjördur were significantly correlated. The mean growth rate was 8.3 and 15.4 cm · yr-1 and 725 and 2254 g · yr-1 for the unconditioned and conditioned cod, respectively. © 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.