Auke Bay Laboratory (ABL)

Stock Identification Program

Yukon River Radio Telemetry Program

The Yukon River chinook salmon radio telemetry program, a cooperative study between the Alaska Department of Fish and Game (ADF&G) and the National Marine Fisheries Service (NMFS), was initiated in 2000 in response to dramatic declines in chinook salmon returns to the Yukon River Basin. The study seeks to improve management and conservation efforts by providing information on chinook salmon migratory patterns, distribution, and run abundance. Work in 2000–01 focused on developing capture methods, tracking techniques, and infrastructure. In 2002–04, researchers conducted a full-scale, basinwide tagging and monitoring program. During 2004, adult chinook salmon migrating upriver were captured with drift gill nets near the village of Russian Mission. Local fishermen were contracted to fish the area, and project personnel were responsible for tagging the fish and collecting data. The gill nets used were effective in capturing chinook salmon while minimizing summer chum salmon bycatch.

A total of 2,132 fish were captured in 2004. Catch per unit effort (CPUE) estimates at the tagging site ranged from 3.4 (Week 22) to 45.0 (Week 24). These estimates correlated closely with weekly capture numbers, especially during the peak of the run (Week 24) when CPUE spiked dramatically. A total of 995 fish were radio tagged during the study. Fish length averaged 826 mm and ranged from 395 mm to 1070 mm. Most fish captured were 6-year-olds (68.4%). A total of 1,092 fish were released without being tagged, 24 fish were recaptures, and 20 fish were handling mortalities. Radio-tagged fish migrating upriver were recorded by remote tracking stations at 39 sites located on important travel corridors and spawning tributaries. Aerial tracking surveys were flown to determine the status of radio-tagged fish in nonterminal reaches of the basin and to obtain movement and distribution information in spawning tributaries. Ninety surveys were flown during the season.

Chinook salmon responded well to the capture and tagging procedure, with 958 (96.3%) fish moving upriver. Movement rates averaged 53 km/day for fish traveling to the upper basin, including 46 km/day for Tanana River fish and 55 km/day for fish returning to the upper Yukon River. Fish returning to reaches in the lower basin traveled substantially slower (34–38 km/day). These rates were comparable to movement information obtained in previous years of the study. A total of 320 (33.4%) fish that moved upriver were harvested in fisheries, including 276 (28.8%) fish in the United States and 44 (4.6%) fish in Canada. An additional 97 fish were recovered or reported by run assessment projects in the basin.

A total of 719 fish were tracked to specific reaches within the basin. Numerous fish traveled into Canada, including 283 (39.4%) Yukon River fish and 8 (1.1%) Porcupine River fish. Most (195,27.1%) Canadian fish were tracked to tributaries of the Yukon River main stem. Fifty-eight (8.1%) fish remained in Canadian reaches of the Yukon River main stem or traveled to associated tributaries not monitored by tracking stations or surveyed by aircraft.

Chinook salmon were also located in U.S. reaches of the upper basin. Substantial numbers of fish returned to the Tanana River (195, 27.1%), and lower numbers were located in other U.S. tributaries. Twenty-four (3.4%) fish remained in U.S. reaches of the Yukon River main stem or traveled to associated tributaries not monitored by tracking stations or surveyed by aircraft. Fish (113, 15.7%) also traveled to tributaries in the lower and middle basin. Although present throughout the run, these lower and middle basin stocks were more prevalent during late June and July. Eighty-nine (12.3%) fish remained in lower and middle reaches of the Yukon River main stem or traveled to associated tributaries not monitored by tracking stations or surveyed by aircraft.

Seventy-seven fish were tagged with radio-archival tags. Fifty-five tags were recovered, including 16 tags in the lower and middle basin, 18 tags in the Tanana River, and 21 tags in reaches of the upper basin. Water depth appears to vary, with fish periodically swimming at depths of more than 20 m. Swimming depth and water temperature data are being analyzed, particularly in reference to movements through areas with fisheries and run assessment projects.

By John Eiler

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AFSC Quarterly Research Reports Jan-Mar 2005