Where do four million fish go in Wood River lakes?

Aug 3, 2017

FRI scientists are walking Hansen creek everyday for ecological studies. Hansen is part of the Wood River system which housed a total escapement of more than four million sockeye this season.

Hansen Creek is part of the Wood River system. It’s a half mile long, about a dozen feet wide and averages a depth of only four inches. Late last month, its mouth was blushing red with thousands of sockeye trying to crawl across the rocky shallows up the creek toward their spawning grounds.

The forecasted sockeye escapement for the Wood River was just over one and a half million this season, but Alaska Department of Fish and Game counting towers have tallied more than four million fish swimming up the river to spawn.

KDLG's Nick Ciolino has the story:

“The size of the stream determines how much area there is for adult salmon to spawn in, and that area will fill up with fish,” said Dr. Daniel Schindler of the University of Washington’s Fisheries Research Institute. “Each female will dig a nest that’s maybe two square yards, and at some point you run out of space and the female salmon start digging up each other’s nests.”

In this way, the size of the water shed acts as a natural regulator of the salmon population, limiting the success of individual fish during a large run.

FRI scientists study salmon carcasses
Credit Nick Ciolino/KDLG

It still remains to be seen where the bulk of the four million sockeye in the Wood will go to spawn. While some creeks are sure to see some over-crowding this year, others may still have average or below average returns, which will typically mean a higher success rate for individual fish who try to spawn. The salmon fry birthed from the river bed next spring may also experience over-crowding in the lake systems.

“Of course it’s interesting,” said FRI ecologist, Dr. Tom Quinn, on the size of this year’s run. “The idea of the escapement goals is you tend to reduce the occurrence of these very large runs, and yet from an ecologist standpoint, we like to see the full range of variation.”

FRI scientists keep a close count of the fish in the Wood River system creeks, as part of a long term data collection dating back to the 1940s. The scientists walk each creek three times per season to tally both the live fish in the streams and the dead carcasses. The dead are further classified by whether they were stranded in the shallows or killed by predators. Many of the carcasses are found missing the head and stomach—a pattern inherent in bear predation.

Sockeye stranded in the shallows.
Credit Nick Ciolino/KDLG

“What the bear consumes from a fish will have implications in bear nutrition, and bear reproduction and bear health,” said UW master’s student Alex Lincoln. “What’s left behind is important for the insects that then feed on those carcasses, as well as the trees who depend on some salmon nutrients, and the greater whole ecosystem.”

FRI scientists walk Hansen Creek every day to study bear predation. Fish eaten by bears are measured and categorized by sex and which part of the fish was eaten. Late in July, the total count of fish to Hansen Creek was 2,059.

“You see a huge range,” said Quinn. “We’ve had as many 60 thousand sockeye three years ago, and in earlier years maybe 500, and that’s not over-fishing, that’s just natural variation.”

It’s still very early in the spawning season, and FRI scientists expect the salmon to continue filing into the narrow waterway well into August.

Contact KDLG fisheries reporter Nick Ciolino at fish@kdlg.org or 907-842-5281