Auke Bay Laboratory (ABL)

Groundfish Assessment Program

Shark Research in the Gulf of Alaska With Sonic and Archival Tags

Scientists from ABL use sonic tags and archival electronic tags to study the ecology and life history of the Pacific sleeper shark (Somniosus pacificus) and spiny dogfish (Squalus acanthias) in Alaska waters. Electronic tags can be programmed to continuously record temperature and depth and have proven to be a valuable tool for gathering information on the geographic distribution and vertical habitat of sharks in Alaska waters. Sonic tags transmit to hydrophones deployed remotely in a fixed array or deployed manually from a vessel that follows tagged animals. Archival tags must be physically recovered to retrieve data.

Sonic tags were surgically implanted in the abdominal cavity of 24 Pacific sleeper sharks in Chatham Strait in southeastern Alaska during June 2004. The sonic tags had a predicted operational battery life of 1 year. Thirteen sonically tagged Pacific sleeper sharks (54%) were acoustically relocated with hydrophones deployed from a vessel in a search area of 588 km² within 1 month after release. The relocated sharks were tracked acoustically at depths greater than 500 m, made horizontal movements of 6 km per day, and made vertical migrations off of the bottom. An array of stationary hydrophones was remotely deployed within the same region 8 months after sonic tag release (February 2005) and recovered 4 months later (June 2005). However, no sharks with sonic tags were relocated with the stationary hydrophones. It is unlikely that all of the sharks with sonic tags left the area. One possibility is that the sonic tags had a shorter than expected operational battery life.

Archival tags were attached externally to the dorsal fins of 41 Pacific sleeper sharks in Chatham Strait in May 2005. A total of 88 Pacific sleeper sharks were tagged with archival tags in Chatham Strait during 2003-05. Archival tags were surgically implanted in the abdominal cavity of 62 spiny dogfish in Yakutat Bay in June 2005. A total of 99 spiny dogfish have been tagged with archival tags in Yakutat Bay during 2004-05. Pacific sleeper sharks and spiny dogfish are occasionally encountered as bycatch in Alaska commercial fisheries. The ABL offers a $200 reward for the return of electronic archival tags. Reward posters have been distributed to the Alaska commercial fishing industry and to the local communities where tags were released. To date, no archival tags have been recovered.

Recovery rates of sonic tags with the remote hydrophones and recovery rate of archival tags have been low (0%). Possible causes for low recovery rates include failure of external archival tag attachment methods, shorter than expected battery life of sonic tags, limited acoustic range and tracking technology for sonic tags, and low interception rates of sharks with archival tags in Alaska commercial fisheries. However, future recoveries of archival tags in the commercial fishery are possible, as the batteries of the tags have a life-expectancy of 10 years. These issues were discussed during a NOAA Advanced Technologies Tagging Workshop held during August 2005 in Seattle.

By Dean Courtney


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AFSC Quarterly
Research Reports July-Sept 2005