Pop-up archival transmitting (PAT) tags: A method to investigate the migration and behavior of Pacific halibut ( Hippoglossus stenolepis ) in the Gulf of Alaska

Pop-up archival transmitting (PAT) tags provide a fisheries–independent method of collecting environmental preference data (depth and ambient water temperature) and migration distance. In this study, we evaluate the use of pop-up archival transmitting tags as a method to investigate demersal fi sh. We report the results from eight pop-up archival transmitting tagged Pacifi c halibut Hippoglossus stenolepis (from 107 to 165 cm FL) that were released in and around Resurrection Bay, Alaska. Commercial fi shermen recovered three tags, while fi ve tags transmitted data to Argos satellites. Horizontal migration was not consistent among fi sh as four Pacifi c halibut remained in the vicinity of release while the other four traveled up to 358 km from the release site. Vertical movement was not consistent among fi sh or over time; however, they spent most of their time at depths of 150 to 350 m. The minimum and maximum depths reached by any of the Pacifi c halibut were 2 m and 502 m, respectively. The fi sh preferred water temperatures of approximately 6°C, but experienced temperatures between 4.3 and 12.2°C. Light attenuation with depth prevented geolocation software and light sensing hardware from accurately estimating geoposition for the majority of days. The methods, adapted from investigations on large pelagic fi sh, proved to be effective for studying Pacifi c halibut in the northern Gulf of Alaska. PAT tags allowed us to obtain high accuracy locations of the fi sh at the end of the tag deployments as well as preliminary data to identify approximate seasonal locations and to characterize their depth and temperature characteristics. By using PAT tags, we will be able to ensure tag returns during the winter season (which is closed to fi shing) and gain valuable biological information even if fi sh migrate large distances or to unexpected locations. Authors: ANDREW C. SEITZ is with the Institute of Marine Science, University of Alaska Fairbanks, P.O. Box 757220, Fairbanks, AK 99775-7220 and the United States Geological Survey, Alaska Science Center, 1011 E. Tudor Rd., Anchorage, AK 99503. Email: aseitz@ims.uaf. edu. DEREK WILSON and JENNIFER L. NIELSEN are with the United States Geological Survey, Alaska Science Center, 1011 E. Tudor Rd., Anchorage, AK 99503. BRENDA L. NORCROSS is with the Institute of Marine Science, University of Alaska Fairbanks, P.O. Box 757220, Fairbanks, AK 99775-7220. Acknowledgments: This project was made possible through the expertise of Capt. Harold Kalve of the F/V Rocinante during fi shing operations; Dave Douglas, Dan Mulcahy DVM, and Julie Meka of USGS-BRD; Susan Ingles, Richard Hocking, Pam Parker, Brian Mullaly, Jessica Dunning and the staff at Alaska Sea Life Center; and Tom Weingartner, David Leech and the crew on the R/V Alpha Helix from the University of Alaska Fairbanks. Partial funding for this project was provided by the Exxon Valdez Oil Spill Trustee Council and the U.S. Geological Survey Alaska Science Center. The fi ndings presented by the authors are their own and not necessarily the position of the EVOS Trustee Council. INTRODUCTION Pacifi c halibut Hippoglossus stenolepis inhabit continental shelf areas from California to the Bering Sea, and from Russia to Japan. Because of their large size (up to 250 kg) and fi ne fl esh quality, Pacifi c halibut have experienced sustained commercial exploitation for the last century (IPHC 1998). The fi shery is managed as a single stock by the International Pacific Halibut Commission (IPHC), a convention between Canada and the United States of America. The Pacifi c halibut population supports one of the most valuable fi sheries in the Gulf of Alaska and eastern Bering Sea. Coastwide landings over the last fi ve years have averaged around 70 million pounds annually, with annual landed values estimated at between $100 and $170 million (T. Loher, International Pacific Halibut Commission, Seattle, Washington, personal communication). Recently, the IPHC has been confronted with a number of local depletion issues, which suggests that movement by adults may be relatively limited. If a geographic pattern of subpopulations exists, it may bear a substantial impact on landing patterns, especially for individuals and communities whose fi shing operations are prosecuted close to their home port. The debate over the relative biological independence of stocks is likely to become more controversial in the near future as IPHC recruitment models indicate that total exploitable biomass has been declining since about 1999 (Clark and Hare 2001). This decline is expected to continue over the next decade as recruitment responds to changes in large-scale environmental forcing (Clark and Hare 2002). It is therefore necessary to investigate the Alaska Fishery Research Bulletin 10(2):124–136. 2003. Copyright © 2003 by the Alaska Department of Fish and Game