Application of Captive Broodstocks to Preservation of ESA-Listed Stocks of Pacific Salmon: Redfish Lake Sockeye Salmon Case Example
Thomas A. Flagg, W. Carlin McAuley, Paul A. Kline, Madison S. Powell, Doug Taki, and Jeffrey C. Gislason
Abstract.—In December 1991, the National Marine Fisheries Service listed Snake River sockeye salmon Oncorhynchus nerka as endangered under the U.S. Endangered Species Act. Snake River sockeye salmon are a prime example of a species on the threshold of extinction, with the last known remnants of this stock returning to Redfish Lake, Idaho. On the basis of critically low population numbers and coincident with the listing, a captive broodstock project was implemented by federal, state, and tribal partners as an emergency measure to save Redfish Lake sockeye salmon. During the decade of the 1990s, a total of 16 wild fish returned to Redfish Lake (0–8 per year); all were captured for the broodstock program. Amplification of the population through captive broodstocking resulted in hundreds of thousands of progeny (prespawning adults, eyed eggs, presmolts, and smolts) replanted to habitats. Between 1999 and 2002, more than 300 adults returned from the ocean from captive broodstock releases—an amplification of almost 20 times the number of wild fish that returned in the 1990s. Important lineages of Redfish Lake sockeye salmon continue to be maintained in culture as preserves for genetic variability and for numerical and demographic amplification of releases to the habitat. It is virtually certain that the broodstock program has, at least for the short-term, prevented extinction of Redfish Lake sockeye salmon. Over the course of the program, operational issues included development of successful captive husbandry procedures, maintenance of genetic diversity, assessment/enhancement of habitat carrying capacity, and intensive evaluation of restocking efforts. In this paper, we discuss these issues as a model approach.