Herring Fishery
Dear Editor: It’s been a week of continuous fishing for the sac roe herring seine fleet, which is closing in on 10,000 tons (20,000,000 pounds) caught this season from a quota of 33,304 tons. Those two numbers are very real, but what about the numbers that they are based on? Are those numbers meaningful or make-believe? I’ve been reviewing all available material on the matter, and I am concerned that Alaska Department of Fish and Game’s herring numerology is off the rails.
Entering the season, ADFG told us to expect a biomass of 210,453 tons of herring in Sitka Sound, 86% of which would come from age-5 herring from the super-dominant 2016 boom class. The average herring weight, they said, would be 112g (109g for those age-5 fish), just above the lower limit of commercial viability. The assumed fecundity (eggs per herring) for herring of that size is 16,250 eggs. The fecundity:weight relationship is derived from a study of herring done in Sitka back in 2005, and is applied to the total estimate of eggs in Sitka Sound – 23 trillion in 2020, an ADFG record – to figure out the biomass of herring involved in the production of that many eggs. If any of those numbers have above-average uncertainty, the likely accuracy of the biomass number quickly fades.
Only two of those numbers seem properly meaningful: 86% or so of the herring which spawned in Sitka Sound in 2020 are now age-5, and there were many more trillions of eggs released into Sitka Sound last year than in all other recent years. Those numbers are established through annual observational surveys of moderate intensity which have continued in the midst of COVID and despite the lack of commercial fishing in 2019/2020.
The other numbers – the weight:fecundity relationship, the assumptions around weight-at-age, and the resulting biomass estimate – demand scrutiny.
Last year and this year, the weight-at-age assumptions were drawn from the results of the 2017 and 2018 commercial test sets. Those commercial test sets are considerably biased to begin with, but it is appalling that ADFG is making conclusions based on outdated weight-at-age data from before the Department even became aware of the dominant 2016 age class.
The fecundity:weight data being applied was derived from herring age/weight/fecundity data collected back in 2005. It is not reasonable to assume that this estimate will be accurate in the context of the dynamics associated with such an unusually dominant age class.
My concern is this: there are a few strong indicators (the department’s under-promoted 2019 and 2020 cast net samples; the commercial test set results; the immediate switch at the start of the season to a co-op model) indicate that herring might be coming in smaller than expected. If, in reality, those age-5 herring are 10-20g smaller than forecast, that would imply that a particularly high number of age 6 and above herring have been targeted and caught on the way to 10,000 tons.
Since no aging is done until the end of the season, we won’t know if this is true until the post-mortem, if we ever learn at all. Big old fat fecund female fish are known to represent population resilience. Their disproportionate removal from the population is a threat to any way of life which relies on healthy marine ecosystems. A massive population of similar-sized small-at-age herring competing for similar-sized feed is something a little bit different than “healthy,” and something much different than a good thing in terms of assuring perpetual annual good opportunity for subsistence harvesters.
I’ve written about this issue in greater depth at: https://arcg.is/1e8bSn.
Peter Bradley, Sitka
