Thermal Mark Technology for Inseason Fisheries Management: A Case Study

Abstract

Effective management of wild and hatchery salmon stocks in Alaska requires rapid and accurate determination of each component in commercial mixed stock catches. Marking 100% of the hatchery fish with thermally induced bands on their otoliths can potentially reduce uncertainty in the management of mixed stock fisheries, this premise being the subject of our investigation. In 1992 and 1993, adult hatchery pink salmon Oncorhynchus gorbuscha that had been thermally marked by prescribed water temperature manipulation in Gastineau Hatchery passed through commercial fisheries on their return to this Southeast Alaska hatchery. In 1993 we processed otoliths that had been collected from the fisheries in 1992. We also applied an inseason recovery plan to process otoliths from the 1993 run; from a random sample of 400 heads collected from each of 5 commercial and 3 experimental fisheries, 100–150 otoliths were subsampled and examined within 24 h to provide managers with inseason estimates of composition. Later, additional otoliths were processed to increase precision around the estimates and to develop quality control criteria. A total of 3,870 heads from the 1993 fisheries were collected, from which 952 otoliths were processed inseason and 1,359 postseason. The final precision, based on the 95% confidence intervals, fell within +2% of the point estimate for each fishery. The accuracy of detecting marked otoliths was determined by planting 17 known marked otoliths into samples processed for the inseason estimate. All planted otoliths were correctly identified. Personnel were trained to process and read otoliths as part of this project. Their progress was evaluated through samples containing both known marked and known unmarked otoliths and by determining between-reader agreement. The results confirmed the importance of training and indicated that, when learning to detect thermal mark patterns, individual skill development varies. We found thermal mark recovery in this study to be a timely and cost-effective tool for managing mixed stock fisheries. 143 Authors: PETER HAGEN and KRISTEN MUNK are fishery biologists with the Coded Wire Tag and Otolith Processing Laboratory, Alaska Department of Fish and Game, Commercial Fisheries Management and Development Division, P.O. Box 25526, Juneau, AK 99802-5526. BENJAMIN VAN ALEN is a fishery biologist with the Alaska Department of Fish and Game, Commercial Fisheries Management and Development Division, P.O. Box 240020, Douglas, AK 99824-0020. BRUCE WHITE is a fishery biologist with Douglas Island Pink and Chum, Inc., 2697 Channel Drive, Juneau, AK 99801 (present address: Alaska Department of Fish and Game, Commercial Fisheries Management and Development Division, P.O. Box 240020, Douglas, AK 99824-0020). Acknowledgments: DIPAC employees Bill Templin, Mike Jaenicke, Kelly Richards, John Turley, and Randy Bates — sampling, dissecting, and preprocessing otoliths; Joe Cashen and Denise Turley — otolith processing; ADF&G managers Don Ingledue, Joe Muir, and biometrician Jim Blick — field and technical assistance. Project Sponsorship: This project was made possible through a cooperative agreement (COOP-93-075) between the Alaska Department of Fish and Game and Douglas Island Pink and Chum, Inc. Alaska Fishery Research Bulletin 2(2):143–155. 1995. Copyright © 1995 by the Alaska Department of Fish and Game