|Publication Type:||Journal Article|
|Year of Publication:||2008|
|Authors:||J. Holmes, Cooke, K., Cronkite, G.|
|Journal:||Reports of California Cooperative Oceanic Fisheries Investigations|
|Keywords:||Aggregation behavior, Article Geographic Terms: INE, Canada, British Columbia, Queen Charlotte Is., Article Subject Terms: Acoustics, Article Taxonomic Terms: Dosidicus gigas, Avoidance behavior, Avoidance reactions, Echo surveys, Fishery surveys, INE, Canada, British Columbia, Vancouver I., INE, Pacific, California Current, Interspecific relationships, ISLANDS, Joints, jumbo squid, marine, marine fish, Merluccius productus, Ocean currents, Pacific hake, predation, Predator prey interactions, Predator-prey interactions, stock assessment, trawling|
During a joint Canada-U.S. Pacific hake (Merluccius productus) acoustic-trawl survey in 2007, 82 jumbo squid (Dosidicus gigas) were captured at depths exceeding 300 m offshore of the continental shelf along Vancouver Island and the Queen Charlotte Islands. Because the acoustic signs associated with these captures were unusual, we compared 38 kHz echograms collected during trawls in which both hake and jumbo squid were caught with those from nearby trawls in which only hake or squid were caught. Hake appeared to be more widely dispersed or less densely aggregated when jumbo squid were captured concurrently. We hypothesize that squid predation causes an avoidance response in hake, thereby altering normal aggregation behavior. Although our evidence of jumbo squid predation on Pacific hake is limited to seven echogram comparisons, this new predator-prey interaction may lead to cascading trophic impacts in the northern California Current. On a practical level, our findings also suggest that the acoustic survey methods, which use a combination of visual echogram interpretation and trawling to verify target identification, will require adjustment. If hake are dispersed over larger coastal areas or do not aggregate as recognizable targets when jumbo squid are present, then additional ship time and other resources may be required for future acoustictrawl surveys.