The use of tagging studies to determine the optimal time for estimating acoustic abundance of spawning cod

Abstract

Abundance estimates of the spawning stock of northeast Arctic cod have, in recent years, been made on the basis of acoustic surveys. Migration in and out of the surveyed areas during investigation has been considered as a possible major source of error in the estimates. This paper evaluates the possibility of using recapture results from tagging experiments to illustrate migration to and from the Lofoten spawning area. Further optimal time period and survey strategy for such surveys are discussed. Tagging-recapture results seem to illustrate the movements of cod around the time of peak spawning reasonably well. Year-to-year variations are demonstrated. It is concluded that the effect of migration on the acoustic estimates of spawning cod in Lofoten is minimized by carrying out the survey during the last 3 weeks of March.