Sitka Sound Roe Herring Forecast, 2016 

Nov. 25, 2015

Sitka Sound roe herring fishery

Sitka Sound roe herring fishery

Sitka. . . The Alaska Department of Fish and Game announced today the preliminary guideline harvest level (GHL) for the 2016 Sitka Sound sac roe herring fishery is 15,674 tons based on a 20% harvest rate of a forecast mature biomass of 78,372 tons.   (The 2015 harvest was 8,712 tons.) 

To forecast biomass, the department uses an age structured analysis model using 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 estimate the density of eggs and the average width of the spawn.

The department mapped 87.9 nautical miles of herring spawn in the Sitka Sound area during the spring of 2015, compared to the recent 10-year average of 60.1 nautical miles. The estimated post-fishery spawning biomass in 2015 was 55,804 tons, the total sac roe harvest was 8,756 tons, and an additional 100 tons were harvested in personal use and test fisheries.

The hindcast of total mature population biomass of 64,660 tons was above the 2015 forecast of 44,237 tons. Estimated age composition of spawning herring in 2015 was 46% age-3, 5% age-4, 21% age-5, 3% age-6, 4% age-7, and 21% age-8+.

The hindcast of 2015 mature biomass exceeded the 2015 forecast primarily because of higher than expected numbers of age-3 recruit herring observed in 2015.

The continued increase of mature herring biomass forecasted for 2016 is primarily due to the continued maturation and return of this large cohort as age-4 fish. Estimated maturation rates suggest that 28% of age-3 herring mature and spawn, and that 81% of age-4 herring mature and spawn. This large difference in percentage mature between age-3 and age-4, together with the large number of mature age-3 fish in 2015, is why greater numbers of this cohort are anticipated in 2016 as age-4 herring.

The forecast indicates that the mature biomass in 2016 will consist of 8% age-3, 66% age-4, 3% age-5, 10% age-6, 1% age-7, and 12% age-8+. The preliminary forecast uses average weights at age from last winter’s test fishery sample and the average weights were as follows: age-3, 75 grams; age-4, 89 grams; age-5, 113 grams; age-6, 141 grams; age-7, 158 grams; and age-8+, 183 grams.

The forecast and GHL for the 2016 fishery will be finalized using average weight at age from samples obtained in the winter test fishery to be conducted in late January or early February, 2016. The final forecast will be announced in late February or early March.