Kootenai River burbot nearing extinction
March 13, 2014
A once thriving fishery, the wild Kootenai River burbot – freshwater cod – is nearing extinction if it doesn’t get help, according to a scientific summary of the burbot in this river that spans two states and British Columbia.

The burbot population in the river was estimated at 150 fish in the mid-1990s and had declined to only 50 fish in the early 2000s. With annual mortality estimated at 63 percent, the wild stock would reach extirpation by 2015. The culprit is Libby Dam and how the dam has been operated since it was built in 1972.

Although there is no new attempt in the works to list the Kootenai River burbot under the U.S. Endangered Species Act (an attempt was made in 2000 to list the fish as threatened, but that petition was denied because the fish did not represent a distinct population segment), Idaho Fish and Game, the Kootenai Tribe of Idaho, the British Columbia Ministry of Environment and the University of Idaho Aquatic Research Institute have signed on to a conservation strategy aimed to bring the burbot back to a sustainable and harvestable population.

“All of the parties involved are committed to working together to ensure that burbot once again thrive as a population (given the current river constraints),” said Ryan Hardy, principal fishery research biologist at IDFG, and one of the summary’s authors. “The conservation strategy is in place and should be instrumental in our efforts to rehabilitate a viable population.”

The strategy includes recovery targets, replacing nutrients in the river and conservation aquaculture in the mainstem and tributaries to supplement the wild stock during rehabilitation, but has yet to include significant changes to Libby Dam’s operations during the critical spawning period in December through February.

“A Synthesis of Kootenai River Burbot Stock History and Future Management Goals” appeared in the November 2013 “Transactions of American Fisheries Society” in a special section on burbot in the Kootenai River and elsewhere in the United States. The synthesis http://dx.doi.org/10.1080/00028487.2013.790845 is by Hardy and Vaughn L. Paragamian, also a fisheries biologist at IDFG.

In Idaho, burbot appear only in the Kootenai River and were at one time an important winter fishery for Native Americans and early Europeans. This and the fishery in Kootenay Lake in British Columbia “may have been the most robust burbot fisheries in North America.” But the fishery declined rapidly after the construction of Libby Dam by the Army Corp of Engineers and by 1992 it had closed completely. The fishery eventually also collapsed in the Kootenay Lake and Kootenay River in British Columbia.

The Kootenai River is the second largest of the Columbia River tributaries. Its multi-national and roundabout journey to the Columbia River begins in Kootenay National Park in southeast British Columbia, flows south into northwest Montana where Libby Dam is located and forms Lake Koocanusa. From there the river flows into the Idaho panhandle, back north into British Columbia to form Kootenay Lake and finally flows into the Columbia River at Castelgar, British Columbia.

Burbot were present in the entire river prior to the construction of Libby Dam, but as two strains. Those above Kootenai Falls (downstream of Libby Dam) are from the Mississippi clade and below the falls the burbot are of the Pacific clade.

The dam has been operated for hydropower production and flood control, impacting the river’s food supply, its temperature and the amount of water released, particularly during the winter when burbot spawn. Higher than normal water temperature and flows from the dam during crucial spawning months have been identified as the major limiting factor on burbot spawning. Add overfishing and the Kootenai River burbot are now near extinction.

One sign of the poor spawning conditions is proportional stock density. Over 46 years biologists have documented an increase in the length of the fish, but with very few young fish entering the population. The average burbot increased in length from 459 millimeters in samples taken in 1957-58 to 615 millimeters in 2002-04 samples. It’s apparent that fewer young burbot are surviving the river’s conditions.

Studies of dam discharges “determined that high winter discharges (especially during power peaking) disrupted the spawning movements of burbot” and in many cases the high discharges forced burbot back downstream. The fish tend to have a low swimming endurance and discharges from Libby Dam in excess of 300 cubic meters per second inhibit spawning migration. Burbot prefer discharges that are less than 176 cubic meters per second.

Temperature also makes a difference. Higher winter discharges also carry higher water temperatures.

All the while, Koocanusa creates a nutrient trap, thus reducing the nutrients in the river below the dam. That has had a negative impact on rearing and overall survival downstream.

IDFG and the Kootenai Tribe of Idaho have added nutrients to both the Kootenai River and Kootenay Lake since 2005. That has been shown “to dramatically increase all levels of the food web, including fish populations that feed directly on macroinvertibrates and diatoms.”

Without an ESA listing, fisheries managers have turned to the conservation strategies to restore the burbot population. Hardy said that it’s reasonable to lay out such strategies when a species is in peril, but not listed under the ESA.

The interim recovery target for burbot abundance is 5,500 age 4 and older fish within 25 years and the ultimate target is 17,500 fish. Much of this will be accomplished through supplementing the wild population.

Following specific protocols, the University of Idaho Aquaculture Research Institute and the Kootenai Tribe of Idaho began stocking in 2009 with 209 larval fish stocked, scaling up to 400,000 larval and juvenile burbot in 2012. Hoop-net sampling by the IDFG indicate that these stockings have been successful. In addition, multiple locations, including historical spawning tributaries, are included in the stocking protocol in order to determine which strategy works best for survival.

Still, the survival of hatchery fish is not thought to be the final solution to the spawning failure of wild burbot, Hardy said, but the hatchery releases and their survival will provide valuable information to determine the potential changes that should be made regarding flow and temperature management at Libby Dam, the final step in the conservation strategy.

“At this point, Libby Dam operations in the winter are not specifically managed for burbot; rather, they are largely based on energy needs,” Hardy said.

Past research suggests that burbot spawning migrations may be disrupted by large fluctuations in winter discharge. Although considered sound science, this research was limited to active tracking technology and a limited number of fish from which to draw specific conclusions, Hardy said.

Since then, the technology of sonic telemetry has advanced, and the number of adult fish that has been tagged in the Kootenai River to aid in evaluating the fluctuating flows has now substantially increased.

According to Hardy, in order to build upon this past research and draft a specific system operation request that will be conducive to spawning, biologists are monitoring fish through multiple spawning periods with a passive sonic tracking array that should give a much more refined understanding regarding effects of present flows and temperatures on spawning.

That SOR will likely include flows less than 176 cubic meters per second and temperatures below 4 degress centigrade during the 40-day incubation period in order for eggs to successfully hatch.