A final forecast won’t be announced until late February, but the Alaska Department of Fish and Game has put the preliminary guideline harvest level for the 2012 Sitka Sound sac roe herring fishery at 29,008 tons. Last year’s guideline harvest level for that fishery was 19,430 tons.
Winter test fisheries for this lucrative harvest will take place in January. The forecast and GHL will be finalized using average weight-at-age from sampling of the winter test fishery, state officials said.
This GHL is based on a 20 percent harvest rate of the forecast biomass of 145,042 tons of mature herring. The forecast indicates that the spawning stock will consist of 13 percent age 3, 24 percent age 4, 25 percent age 5, 14 percent age 6, 11 percent age 7, and 13 percent age 8 and older herring.
State biologists use an age-structure-analysis model to estimate abundance, survival rates and maturation rates needed to forecast the biomass of mature herring expected to return to Sitka Sound during the upcoming spawning season. The model uses a long time series of abundance and age composition data from department surveys conducted during and following the spring fishery.
Herring abundance is estimated using aerial surveys designed to map the length of shoreline receiving spawn, and dive surveys, which estimate the density of eggs and the average width of the spawn. In the spring of 2011, the department documented 78.3 nautical miles of herring spawn in the greater Sitka Sound area.
Last year the ASA model estimated 132,000 tons of herring spawned in the Sitka Sound area and the commercial sac roe herring harvest was 19,430 tons for a total return of 151,430 tons.