ADF&G’s Togiak Herring Forecast is Robust

Alaska Department of Fish and Game
Alaska Department of Fish and Game.

Alaska Department of Fish and Game officials say the 2022 mature herring biomass forecast for Togiak is 357,536 tons, the highest forecast since an age-structured assessment model was first used for the 1993 forecast.

Given the 20% exploitation rate, the coming year’s potential harvest is 71,507 tons in all fisheries and 65,107 tons in the Togiak sac roe fisheries, which are harvested with purse seine and gillnet gear. The gear group allocation specified in the Bristol Bay Herring Management Plan is for 80% purse seine and 20% gillnet.

Togiak herring are targeted for their roe, but those markets have been declining in recent years.

A year ago, the harvest forecast was for 47,348 tons of herring in all Togiak fisheries and 42,639 tons in the Togiak sac roe purse seine and gillnet harvest.

“The buyers in 2021 in Togiak were Silver Bay and Icicle,” Tim Sands, area management biologist for ADF&G in Dillingham said. “Typically buyers like to get as big of fish as they can get and hope to start out with 400+ gram fish for the first few days. Ideally they would have all their harvest average above 350 grams. We have not seen that for the last couple of years.”

“These very large age classes of 5- and -6-year-olds in 2022 will skew the average size lower from the very beginning,” he explained. “It will remain to be seen what the average size is at the start and how quickly it drops.”

State biologists said the large 2022 forecast is due primarily to the largest estimated recruitment of age-4 fish on record in 2021. That’s about 1.5 times larger than the large recruitments seen in the early 1980s and one of the largest recruitments on record in 2020. These cohorts are projected to make up an even larger portion of the 2022 population due to increasing maturity.

The majority of the mature population for the year ahead is age-5 and age-6 fish, both by number – 52% and 20% respectively, and by biomass – 45% and 21%, respectively.

The average weight of herring in the 2022 mature population is forecast at 281 grams. The forecast average weight of a fish vulnerable to the commercial purse seine fishery is 297 grams.

The biologists noted that the forecast has considerable uncertainty, largely due to the recruitment component of the age-structured assessment model. While uncertainty estimates are not yet produced for Togiak forecasts, there is considerable uncertainty in the 2022 forecast due to the recent large age-4 recruitment events and the resultant uncertainty in the forecasted numbers of age-5 and age-6 fish Togiak herring in 2022.

Herring are detected in the Togiak sampling when they recruit into the fishery, a process that begins around age-4 and may not complete until about age-9. Large recruitments in this population generally occur every eight to 10 years and typically last one or two years.