Age, growth and otolith annulus formation of cod (Gadus morhua) in the Risør area on the Norwegian Skagerrak coast during 1986–1996

Abstract

Cod (Gadus morhua L.) were collected using a trammel net in the Risør area on the Norwegian Skagerrak coast. About 2100 fish were examined, measured, some weighed, and otoliths were collected. Otoliths were used for ageing and for back-calculation of growth. Otolith zone formation differed from that observed in most other areas, as the opaque material was deposited mainly during winter and spring. The oldest fish recorded was 8 years old, but more than 90% were 3 years old or younger. Differences in growth were small between the sampling areas, although fish from the Risør Skerries, an open coastal area, grew slightly faster than those from the fjords in the Risør area. Compared to cod stocks from most other areas, cod from the Risør area at the Norwegian Skagerrak coast have a slow growth. Year classes showed significant differences in growth, but no correlation was found between growth and year-class strength.

Keywords:

• Age
• Cod
• Gadus morhua
• growth
• otoliths
• Skagerrak coast

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

Thanks are due to Mrs K. Enersen for reading the otoliths and for participating in all phases of this project, Mr S. E. Enersen, Mr Aa. Sollie and the captain and crew on R.V. ‘G. M. Dannevig’ for help with the fishing operations. We are thankful for constructive comments from the referees on a previous version of this paper.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark