JUNEAU, Alaska — The Alaska Department of Fish and Game said it has been overestimating how many Chinook and sockeye salmon make it up the Taku River.
Department officials said the statistical bias is being corrected by new state-of-the-art studies, the Juneau Empire reported Sunday.
The department said it had been overestimating the salmon numbers by 30 to 40 percent. The estimates were conducted using a decades-old “mark-recapture” system.
Department coordinator Ed Jones said seal predation and the old system have caused much of the problem.
The department uses a series of buckets, called a fish wheel, to scoop salmon from the river and deposit them in a holding tank. The Canyon Island fish wheel has been in the same place since the 1950s, only, “It used to be wooden, now it’s aluminum,” Jones said.
The wheel turns 24 hours a day while in operation during the summer months. The problem, Jones said, is that staying in the holding tank can cause fish to become lethargic when released later on. Biologists refer to is as a “sulk rate” and it leaves fish open to predation.
Jones said there’s a big herd of seals that sit down river of Canyon Island, preying on the “sulking” fish.
Seals would pick off a small amount of these fish naturally, Jones said, which means they might not be overestimating by quite as much as radio telemetry studies suggest. He estimated the amount of stunned fish lost to seals to actually be around 30 percent.
The department said that the discrepancy doesn’t mean either of the stocks are any worse off than they have been, but fishers are concerned the bias could impact ongoing negotiations with Canada over who has the right to harvest sockeye since both countries fish on the river.
Information from: Juneau (Alaska) Empire, http://www.juneauempire.com