An ongoing study of Wallowa Lake’s kokanee and their food sources aims to improve lives of kokanee, and also help fisheries biologists understand if the lake has the resources to support reintroduction of sockeye.

{span}It might be easy for the casual observer to think Northwest fishery management is all about the big stuff: big rivers, big dams, big projects, big dollars. {/span}But at Wallowa Lake, fishery co-managers are focusing in on the little stuff, too. Not only is there hope the added perspective will help with the management of the lake’s current salmon population, it might even help inform future efforts to bring another one back.

Kokanee are the salmon species in Wallowa Lake today — the same species (Oncorhynchus nerka) as sockeye. Kokanee are the land-locked version of sockeye — or rather the sockeye who choose to stay at home and not migrate to the Pacific. (This is much the same as steelhead and rainbow trout — both the same species, but steelhead migrate to the ocean snd rainbows stay in their home streams.) the sockeye having were exterpated from the lake system about 1904 through fishing and the construction of the dam.

Biologists know kokanee feed primarily on an array of tiny aquatic critters called zooplankton. These tiny organisms are found throughout the lake in a variety of species, abundance, densities and depths. A micro-sized shrimp called “mysis” is in the lake too, introduced in 1965 in hopes of growing bigger kokanee. But co-managers believe mysis tend to occupy different depths and are not a large part of the kokanee’s current diet.

Pieced together with water chemistry and other factors, variables such as these comprise what biologists call the kokanee’s “food web,” something co-managers hope to better understand. Not surprisingly, what happens in the food web determines much of what happens with the kokanee.

“Kokanee feed on zooplankton in the water column,” said Kyle Bratcher, acting district fish biologist for the Oregon Department of Fish and Wildlife in an e-mail. “Anecdotal information suggests that plankton abundance also fluctuates and is likely a main driver in kokanee abundance and size. This is something we are hoping to better understand with the food web study.”

Since last year, a partnership made up of the Nez Perce Tribal Fisheries, ODFW and the U.S. Geological Survey has been conducting sampling work toward developing a working model of the kokanee food web.

“We took several zooplankton samples in 2019 and will again in 2020,” said Shane Vatland, research project leader with Nez Perce Tribal Fisheries in an e-mail. “We also collected kokanee stomach samples. So, we will get a clearer picture of what exactly kokanee are eating and how many are available in the lake.”

Co-managers know Wallowa Lake kokanee tend to cycle in size and abundance over periods of years. In 2010, Ron Campbell from Pendleton landed the standing world record kokanee here (9 pounds, 10 ounces), and several other unusually large fish were caught around that time. Subsequent years saw a return more toward normal. Ongoing annual surveys measuring kokanee spawner size and sex offer some clues as to what might be coming in future years, but why is what co-managers would like to better understand. The hope is that the combination of survey data and food web modeling will give co-managers new tools to use in making management decisions.

“The kokanee population is highly cyclical on an eight- to 12-year cycle,” Bratcher said. “The size of kokanee dropped after those years when the records were being broken. We have seen sizes increase in the last few years with some larger fish on the spawning grounds this year. Part of the food web study is to help us understand this cycle, as it appears to be highly food-driven.”

In addition to knowing what kokanee are eating, another important metric in their overall assessment is what’s eating them. Wallowa Lake does have a population of nonnative lake trout, which tend to feed voraciously on other fish, including kokanee when conditions are right. Bratcher said while they will continue to closely monitor lake trout interaction with kokanee, he does not believe lake trout predation is a large driver in kokanee abundance at this time.

Recent discussions surrounding the reconstruction of Wallowa Lake Dam have included the primary infrastructure changes necessary to begin to think about reintroducing sockeye, namely passage for fish out of and into the lake at the dam site. Restored fish passage would represent an enormous step toward that goal, but still clearly one of an unknown number facing those working to achieve sockeye reintroduction successfully.

Partners working on the Wallowa Lake kokanee food web project say the insights gain to better understand kokanee could be useful in any future sockeye reintroduction efforts as well. Juvenile sockeye in freshwater tend to feed largely on zooplankton, for example, just as kokanee do.

“The food web study could inform us how to approach a sockeye reintroduction in the future in terms of numbers and timing of releases,” Bratcher said.

Partners expect to have a working food web model completed by 2021.

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