The GHL, based on a 20 percent harvest rate of a forecast mature biomass of 73,245 tons, compares with the preliminary GHL of 15,674 tons for 2016, based on a 20 percent harvest rate of a forecast mature biomass of 78,372, of which just under 10,000 tons was landed.
ADF&G said that their forecast issued on Dec. 12 would not be updated with winter test fishery weights, as was the practice in previous years. The change was made to save on costs associated with processing winter test samples and staff time developing and reporting an updated forecast and GHL. The accuracy of the forecast was not expected to be impacted significantly by not updating the model with the winter test fishery weights at age due to the relatively small variability seen in weight at age, the agency said.
The forecast indication was that the mature biomass in 2017 would consist of 6 percent age-3, 6 percent age 4, 73 percent age-5, 2 percent age-6, 6 percent age-7 and 7 percent age-8+. The forecast used spring commercial purse seine weights at age from last year’s fishery and average weights were age-3, 64 grams; age-4, 95 grams; age-5, 104 grams; age-6, 132 grams,; age-7, 149 grams; and age 8+, 178 grams.
The department mapped 63.3 nautical miles of herring spawn in the Sitka Sound area in the spring of 2016, compared to the recent 10-year average of 65 nautical miles. The estimated post-fishery spawning biomass in 2016 was 74,676 tons, the total sac roe harvest was 9,833 tons, and an additional 223 tons were harvested in personal use and test fisheries.
Estimated age composition of spawning herring in 2016 was 2 percent age-3; 79 percent age-4; 2 percent age-5; 8 percent age-6; 1 percent age-7, and 8 percent age 8+.
State biologists said the mature biomass forecast for 2017 was similar to the spawning biomass in 2016 because the increase in maturity of the 2012 and 2013 cohorts and the additional age-3 recruits in 2017 balanced the decreases due to natural mortality.