Daily Sitka Sentinel

Herring Catch Set At 33K Tons; May be Less

By Sentinel Staff

The 2021 guideline harvest level for this year’s sac roe herring fishery has been set at 33,304 tons, the state Department of Fish and Game announced today.

“However, based on input from processors involved with the Sitka Sound sac roe herring fishery it’s expected that the commercial harvest in 2021 will not exceed 20,000 tons,” said Area Management Biologist Aaron Dupuis, speaking for Fish and Game in today’s statement.

He said the age 5 class is forecast to be “unusually large,” comprising – by number of herring – some 86 percent of the returning population this spring.

The fishery generally takes place in more than one opening in late March, depending on sample results among other factors.

No herring fishery was held in 2020 due to the smaller size of herring and market conditions, and none was held in 2019 after marketable herring couldn’t be found. The GHL for 2020 was 25,824 tons.

Dupuis explained the 2021 estimate was calculated by reducing the GHL derived from the Age Structured Analysis by 21 percent. This “approximates the harvest level available if the number of age 5 fish is 75 percent of that projected.”

“This precautionary approach in determining the GHL takes into account the higher-than-usual uncertainty in the forecasted return of the unprecedented large age class of age 5 herring,” he said. “The size of the forecasted 2021 age 5 herring cohort is unusually large and is more uncertain than other year classes due in part to the magnitude of estimated abundance and the impact of uncertainty in estimated maturity and survival.”

Dupuis said the department has observed the 2016-year class of herring as age 3 fish in 2019, and as age 4 fish in 2020, so the overall uncertainty with the 2021 forecast is less than that of the 2020 forecast.

“This extremely large year class has been observed in other herring populations throughout the Gulf of Alaska in 2019 and 2020,” Dupuis wrote. “The 2021 ASA forecast of mature herring biomass is 210,453 tons of mature herring.” That’s the second largest for Sitka Sound herring, but 16 percent smaller than the 2020 mature biomass estimate of 250,468 tons, Dupuis said.

He said the composition of the expected returning biomass by number of herring is:

- 2% age 3

- less than 1% age 4

- 86% age 5

- 5% age 6.

- 3% age 7

- 4% age 8+.

(Although the ages are broken down by numbers of herring, the breakdown is roughly the same when calculated by biomass, Dupuis said today.)

He explained some of the unusual circumstances this year:

“Because there was no commercial harvest in 2019 and 2020, the forecast used an average of the spring commercial purse seine weights at age from the 2017 and 2018 fisheries harvest: age 3, 79 grams; age 4, 92 grams; age-5, 109 grams; age 6, 126 grams; age 7, 144 grams; and age 8+, 165 grams.”

He said the forecasted average weight across all age classes is 112 grams for this season.

Explaining how Fish and Game forecasts the biomass, Dupuis said the department uses an ASA 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.”

He noted the department mapped 58.5 nautical miles of herring spawn in the Sitka Sound area during the spring of 2020, compared to the recent 10-year average of 60.6 nmi. 

“Egg deposition in 2020 was the highest on record since 1976 and was nearly three times the 2019 estimate, due in part to the increasing maturity of the 2016-year class,” he said. “A large proportion of the eggs were observed along the southern and outer shores of Kruzof Island but, unlike 2018 and 2019, eggs were also spawned along the Sitka road system and among nearby islands.”

The estimated age composition by number of spawning herring in 2020 was: less than 1% were age 3; 88% were age 4; 5% were age 5; 3% were age 6; less than 1% was age 7; and 4% was age 8+.