Capture of wild saithe (Pollachius virens) and cod (Gadus morhua) in the vicinity of salmon farms: Three pot types compared

Large numbers of wild members of commercially important fish species tend to congregate around fish farms. This effect is in conflict with the interests of fishermen because wild fish cannot be harvested close to fish farms due to the fishery exclusion zone, which is intended to prevent fishing gear from damaging the cages. We studied the potential for harvesting wild fish around a Norwegian salmon farm using three different types of pots. Our video observations showed that large quantities of wild fish, in particular saithe (Pollachius virens), aggregated in close vicinity of the cages. Pots set underneath salmon cages produced 17 times higher catches of saithe and five times higher catches of cod (Gadus morhua) than pots set at a distance of 100 m from the cages. The pots set underneath cages also caught larger cod. Large rigid pots were shown to be more efficient than smaller flexible pots. The stomach content of small cod was dominated by pellets, while large cod were feeding mainly on saithe. We suggest that dense aggregations of saithe and small cod beneath fish cages were associated with the supply of waste feed, whereas larger cod were attracted by the saithe. We conclude that pots have great potential for harvesting gadoids beneath salmon cages, but catches decline dramatically with the distance from cages.