2019 Sitka Herring Harvest Announcement - P.O.W. Report

Wednesday, December 5, 2018

2019 Sitka Herring Harvest Announcement

[Sitka December 3, 2018] The Alaska Department of Fish and Game announced today the guideline harvest level (GHL) for the 2019 Sitka Sound sac roe herring fishery is 12,869 tons based on a 20% harvest rate of a forecasted mature biomass of 64,343 tons. The 2019 forecast is more than the 2018 forecast of 55,637 tons but less than the 2016 and 2017 forecasts (74,707 and 73,245 tons). This forecast is a 9% increase from the model estimate of 2018 mature pre-fishery biomass of 59,257 tons.

Results of the spawn deposition survey revealed that although spawn mileage was approximately half that of 2017, the spawn extended nearly twice as far offshore, and egg density was higher. In 2005 and 2008, a similar situation occurred where the spawn extended far offshore on Kruzof Island due to the very wide shelf of herring spawning habitat. Therefore, due to exceptional spawn along the Kruzof Island shoreline, the 2018 herring spawning biomass was much higher than was apparent from the spawn mileage alone, highlighting the need to conduct annual spawn deposition surveys.

The forecast indicates that the mature population in 2019 will consist of 12% age-3, 43% age-4, 21% age-5, 2% age-6, 18% age-7, and 4% age-8+. The forecast uses spring commercial purse seine average weights at age from last year’s fishery harvest: age-3, 80 grams; age-4, 96 grams; age-5, 101 grams; age-6, 127 grams; age-7, 151 grams; and age-8+, 155 grams. Like the previous two years, this forecast will not be updated with winter test fishery weights as had been done prior to the 2017 fishery.

To forecast biomass, the department uses an age-structured assessment model with a long time series of egg abundance,and age composition data from department surveys conducted during and following the spring fishery. Herring egg abundance is estimated using aerial surveys,designed to map the length of shoreline receiving spawn,and dive surveys,which are used to estimate the density of eggs and average width of the spawn. The department mapped 33.1 nautical miles of herring spawn in the Sitka Sound area during the spring of 2018, compared to the recent 10-year average of 66.6 nautical miles. The estimated post-fishery spawning biomass in 2018 was 56,248 tons,the total sac roe harvest was 2,926 tons, and an additional 82 tons were harvested in test and personal use fisheries.Estimated age composition by number of spawning herring in 2018 was 21% age-3, 30% age-4, 5% age-5, 36% age-6, 2% age-7, and 6% age-8+.

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