Analysis of long-term Atlantic cod tag-recapture data from Norway reveals insights into historical migration patterns and mortality rates of Norwegian coastal cod

Abstract As global fishery resources face increasing pressure, robust data are essential for implementing sustainable management practices. Key insights into migration patterns, connectivity, and mortality rates, both natural and fisheries-induced, are essential for effective management strategies. This study presents a unique tagging and recapture dataset of Atlantic cod. Within this dataset, we focussed on mortality rates and displacement distances of Norwegian coastal cod (NCC), including 23 231 cod released between 1954 and 1983 across four specific release zones north of 62°N, along with 7010 recaptures. Specific subsets of these data were chosen for targeted statistical analyses. Our findings indicate that mean instantaneous total annual mortality (Z) of NCC was >1.0, and possibly even higher in the southern area. NCC tagged during the feeding season (June–October) displayed median displacement distances of 33–115 km, with 5%–35% of individuals dispersing >200 km, and 2%–15% dispersing >500 km. Displacement distances increased with time between tagging and recapture, size at tagging, and was highest for fish recaptured during the spawning season and in the northern zones (Finnmark). These results suggest stronger connectivity between fjords and coastal areas in northern Norway than further south. The size of the release zones used in this study (ranging from 8000 to 29 000 km2) align with NCC’s generally limited dispersal in the southern zones, highlighting their potential as management units, while further analyses are needed for the northern zones.