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Adult sockeye and pink salmon tagging experiments for separating stocks in northern British Columbia and southern Southeast Alaska, 1982-1985

Abstract

Adult sockeye (Oncorhynchus nerka) and pink (O. gorbuscha) salmon were captured, tagged, and released in coastal fisheries of southern Southeast Alaska and northern British Columbia between 1982 and 1985. Sockeye salmon were tagged in 1982 and 1983; pink salmon were tagged in 1982, 1984, and 1985. The tagging experiments were part of a cooperative effort by the United States and Canada to assess contributions of stocks of each country to fisheries of the region and to learn about the coastal migrations of these salmon.

Catches and escapements in Alaska and Canada were sampled for the purpose of estimating numbers of tagged fish that either were caught among or escaped to contributing stocks. Estimated numbers of tagged fish in catches and escapements were used to assess stock composition of catches of the fisheries during the tagging years.

Most sockeye salmon in Alaskan fisheries were of Canadian origin, and only a small percentage of the catch in Canada was of Alaskan origin. Alaskan sockeye salmon were relatively more numerous in 1982 than in 1983, compared to Canadian stocks of those years. Sockeye salmon from the Canadian Nass and Skeena Rivers constituted major portions of catches of most fisheries. In 1983, southward-migrating stocks, probably mainly from Canada's Fraser River, occurred in outer coastal fisheries of Alaska and Canada, and in Canadian fisheries at the southern end of the study area.

Most pink salmon in nearly all Alaskan fisheries throughout the season were of Alaskan origin. Only in two of nine Alaskan fishing areas examined did the percentage from Alaskan stocks drop below 75% at times. Percentage of Alaskan pink salmon in Canadian fisheries was also substantial, but more variable among areas and years of tagging than in Alaska. In Canada, percentage of Alaskan pink salmon was generally greatest in areas adjoining Alaska.

The interpretation of the experiments for assessing stock composition in fisheries was fraught with difficulties. Among the shortcomings were large potential errors in estimates of numbers of tagged fish escaping to the spawning grounds. However, numerical studies showed that stock-composition estimates for sockeye or pink salmon would generally not be misleading because of such errors. Lack of information on stock origin of tagged fish caught in intervening fisheries and the apparent incomplete accounting for tagged fish in sampled catches and escapements were further deficiencies whose potential effects on stock-composition estimates were not examined.


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