Acoustic Conditioning to Reduce the Impact of Escapement in Atlantic Salmon (Salmo Salar) Net Pen Aquaculture

Net pen culture is the most common method used to raise salmon, however these farms are typically located in areas through which wild salmon inhabit or migrate and escapes may influence wild stocks. Commercial salmon farms can potentially reduce both economic losses to the producer and impacts on wild stocks by recapturing escapees. Acoustic signaling has been used to concentrate fish species for feeding or harvest and to deter fish from specific areas. The present study investigated the approach of conditioning salmon to associate a tone with feeding to entice return to a specific location allowing recapture. The ability of juvenile and sub-adult Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss to detect various frequencies within their hearing range (below 380 Hz) was assessed. Subsequently, the fish were conditioned to associate a 250 Hz pure tone with feeding. Juvenile and sub-adult fish readily conditioned to acoustic signals (87 % in salmon and 97 % in trout) over a period of 4 - 7 days. Following initial conditioning the fish retained the training, regardless of the degree of reinforcement (exposure to a single tone every one, two or four weeks) for a 6 month period without a significant decrease (88 % in salmon and 97 % in trout). No significant differences were observed in either species in response to signal frequency (89 % in salmon and 96 % in trout) or intensity (91 % in salmon and 96 % in trout). Preliminary release and recapture trials conducted in Narragansett Bay to determine the feasibility of recovering fish did not result in return of fish