Home ranges and spatial segregation of cod Gadus morhua spawning components

Abstract

The study analyses the home ranges and spatial segregation of spawning components of Icelandic cod Gadus morhua based on: (1) conventional tag (CT) recaptures and (2) depth, temperature and tidal locations from electronic data storage tags (DSTs). A total of 5987 CT recapture positions from tagging in geographically distinct spawning grounds from 1991 to 2008 were used in the home range analysis. Despite long-distance feeding migrations conducted by individuals within all groups and feeding home ranges of 25 000 to 125 000 km2, the study revealed a low spatial overlap among a number of spawning components throughout the year. A high fidelity to spawning grounds within most spawning components studied further indicates a strong spatial structure within the cod population. Results from CTs and home range analysis were supported by geographical tidal locations from DSTs. On the other hand, data from 235 DSTs indicate that foraging migrations to depths of 400 to 800 m are underrepresented by conventional mark-recapture methods. This study contributes to the growing knowledge of the within-population diversity and demographic structure of cod and further emphasizes the need for considering these factors in fishery management.