Estimating Abundance for Management of Yukon River Salmon Harvest and Escapement

Within the Alaska portion of the Yukon River drainage three species of Pacific salmon (Chinook salmon Oncorhynchus tshawytscha, coho salmon O. kisutch, and chum salmon O. keta) are managed in season for harvest by commercial, sport, and subsistence fisheries, as well as to meet treaty commitments made under the U.S. / Canada Yukon River Salmon Agreement. The diversity and number of salmon stocks, combined with the geographic range of user groups, adds further complexity to management decisions. While a variety of sources (including gillnet, fishwheel, weir, and sonar projects) generate timing and run-strength indices, much of this information is of limited inseason management value, being obtained after the fish have become unavailable to the fisheries, or because they do not provide historically consistent measures of abundance. Obtaining abundance information timely enough to base management decisions on is complicated by the sheer size, volume, and silt load in the mainstem river, along with the presence of a large number of non-target fish species. To estimate both abundance and timing, the Alaska Department of Fish and Game operates four sonar projects in the Yukon drainage, with two located on the mainstem (one near the mouth of the river and one at the border) and two on tributaries (one in the lower river and one in the upper river). These projects share a number of commonalities, yet each also serves a unique purpose and contributes to the overall long term historical record.