Tagging experiments on artificially reared 0-group coastal cod (Gadus morhua L.) in western Norway - results from the releases in 1984

Abstract

In November - December 1984, 8,038 seven to eight month old pond or basin reared cod fry were tagged and released in Heimarkspollen, a landlocked fjord in western Norway. The aim of this study was to investigate whether recapture rate (survival) was influenced by tagging method, release method or size at release, and to study the growth pattern of the different size groups after release. The juveniles were graded in four size groups and tagged with either Internal Steal Tags or Floy Anchor Tags. The fry were released in shallow nearshore waters one by one or in small groups. Tag return to 1 June 1987 from fishing surveys and recaptures reported by local fishermen were 7.6 %. There were no significant differences in percentage recaptured between cod tagged with Internal Steal Tags and Floy Anchor Tags or between single and group released fry. The recapture rates increased with increasing size at release, which indicated size dependent mortality. There was a tendency of growth compensation in the smallest size groups, and for recaptured cod older than two years there was no significant difference in mean length at age between the size groups.