Post-escape dispersal of juvenile Atlantic cod Gadus morhua from Norwegian fish farms and their potential for recapture

Abstract

The escape of fish from sea-based aquaculture facilities is regarded as a potential environmental threat and is one of the biggest challenges the industry has faced in recent years. In addition to preventing escapes by improving farming operations and procedures, effective and operational routines are needed for recapturing fish should an escape occur. This study investigated the post-escape dispersal of juvenile Atlantic cod Gadus morhua L. from commercial sea cages in coastal Norway using acoustic telemetry. It also assessed the efficacy of different techniques (e.g. cod pots, fyke nets, and gill nets) for recapturing escaped fish. Results suggest that escaped juvenile cod can experience a high size-related predation pressure immediately after escape due to high numbers of large fish aggregating around the cages. Consequently, the escapees rapidly disperse from the farms and seek shelter in littoral areas. Once in shallower waters, they stay relatively close (<10 km) to the farm during the first 2 mo following an escape. This suggests a high potential for recapture if the effort is focused on the littoral area and not in the immediate vicinity of the farm. No escapees were caught using live recapture methods, and a low number of recaptures (<5%) were achieved with gill nets deployed in littoral areas. Moreover, high by-catch rates and a subsequent high workload suggest this method may be inappropriate for the recapture of escapees.