Northern and Transboundary Sockeye Matched Scale-Tissue Sampling

Provisions of the 1999 Pacific Salmon Treaty (PST) specify abundance-based harvest sharing arrangements of Nass and Skeena River sockeye salmon returns for the U.S. and Canada. The United States is allowed to harvest a fixed percentage of the annual allowable harvest of Nass and Skeena sockeye stocks in Alaska’s District 101 gillnet and District 104 purse seine fisheries. Accurate estimates of the stock-specific catch in commercial fisheries of each nation are required to estimate the total return of these stocks and the percentage of each stock caught in treaty-limited fisheries.
Since 1982, scale pattern analysis (SPA), sometimes in conjunction with other biological markers, has been used to survey the weekly catch of Northern Boundary and Transboundary sockeye salmon stocks in Southeast Alaska fisheries. However, problems in accurately estimating stock-specific catches and total returns of sockeye salmon in the early years of the Pacific Salmon Treaty resulted in an extensive investigation, and it was concluded that improved stock identification techniques, such as genetic stock analysis, were needed to accurately evaluate effectiveness and improve, if possible, existing run reconstruction methods. Two blind tests of scale analysis vs. genetic analysis demonstrated that, while both techniques were accurate, the genetic analysis had higher precision and could also often identify many specific stocks, while scale analysis is limited to identifying a few stock-groups. Neither technique can identify enhanced fish where the brood stock came from wild stocks that are also present in the mixed stock fisheries; thus, otoliths are used in annual stock composition estimates and run reconstructions.
ADF&G proposes to continue collecting weekly otolith, tissue, and scale samples of sockeye from the Southeast Alaska commercial harvest in the District 101 gillnet and District 104 purse seine fisheries, among other districts and fisheries for projects that complement this program. Stock identification analysis using age composition, thermal mark presence, and new, more stock-discrete DNA techniques will be conducted at NOAA’s Auke Bay Laboratory. This project also complements the continuing work by DFO in Areas 3, 4 and 5.