Tribe working to bring back burbot
The tribe is spearheading an effort to revive a native burbot – freshwater cod – population that as recently as 2003 was estimated to include fewer than 50 wild burbot spawners.
Finding an adult spawner has been probably harder than finding a needle in the proverbial haystack.
The number of burbot encountered during Idaho Department of Fish and Game wintertime surveys “got progressively worse until we started putting in hatchery fish,” said Shawn Young, a fishery biologist and researcher with the tribe’s Fish and Wildlife Department. That experimental aquaculture program began in 2003 in collaboration with the University of Idaho.
The research program at the UI has fed small, though increasing, numbers of hatchery produced fish for release into the system since 2009. Now some of the surviving members from that 2009 release – 36 or so based on year-to-year survival estimates – should have advanced to 100 percent sexually maturity.
“They should be looking for some spawning partners,” Young said of the survivors.
Known spawning areas will be monitored for the presence of fish. Those tributaries are where releases were focused. Biologists will also check out “candidate” areas where there is coarse, gravel substrate that burbot seem to prefer.
Through the years the hatchery releases have been equipped with PIT-tags and in the case of some larger fish, acoustic tags that can be detected by receivers. Much of the trapping, tagging and monitoring is carried out by the Idaho Department of Fish and Game.
Burbot are known to come together and form “spawning balls with dozens of fish in each congregation,” Young said. Eggs dropped by females are fertilized in the water column by sperm from the males. The fertilized eggs then drop where they may.
Young and other biologists have witnessed the phenomenon (with the help of an underwater camera) at British Columbia’s Moyie Lake. The lake, just north of the Idaho-Montana border at the head of the Moyie River, has a healthy burbot population and has been the source of broodstock for the experimental hatchery program. The Moyie River flows out of the lake and empties into the Kootenai River.
Spawning is expected in February.
Spawning-time monitoring will be looking for such aggregations of fish. On average eggs hatch out about 50 days after the spawning event, but timing depends on the water temperature.
“They spawn in the coldest part of the year,” Young said, often under ice with river temperatures barely above freezing at 1-2 degrees C.
The 2009 releases included 179 1-year-olds, 23 2-year-olds and seven 3-year-olds. Burbot have been known to reproduce as early as at age 2, but for the vast majority 4 and older is the primary reproductive age.
From 2009-2012 at total of 1,670 1 to 3-plus-year-old sub-adults have been released, including 653 1-year-olds last year. They have been shown to survive through their first year in the wild at a rate of up to 50 percent.
Another 39,000 burbot have been released as six month old juveniles, including 16,000 in 2012. They are estimated to have a first-year survival rate of about 25 percent.
“That’s the life stage we’re targeting” for the bulk of the releases, Young said. The 6-month-old fish can be grown in greater numbers, and with less hatchery space for each fish, than the older fish.
Additionally, 314,000 burbot larvae hatched out at the UI have been released, including 265,000 in 2012.
“We have no idea what kind of survival we’re talking about” with the larvae, though it is almost certain to be much lower than for the older releases, Young said.
“Almost all of them went into Kootenay Lake,” Young said. The lake is generally warmer than the river or its tributaries, and has a better early season supply of zooplankton, which need to begin feeding about 10 days after they hatch out.
Biologist have seen dispersal of the released hatchery burbot throughout system, which stretches approximately 150 miles from the Kootenai-Moyie confluence on the east side of the Idaho panhandle downstream to the upper end of the Lardeau River Delta in the North Arm of Kootenay Lake. The mean dispersal of all released burbot was 50.5 km (31 miles).
The project is being carried out in collaboration with the British Columbia Ministry of the Environment, IDFG, U.S. Fish and Wildlife Service and the UI’s Aquaculture Research Institute.
Basic culture methods have now been established and documented for spawning, egg incubation, larval rearing and juvenile grow out. Hatching and rearing techniques have been honed by UI researchers to the point that larvae are being produced in relatively large numbers.
Among the goals of the Kootenai Tribe’s program, which is largely funded by the Bonneville Power Administration, is to implement a plan to reverse the population decline through habitat restoration, and research to identify and address gaps in understanding of the specific causes of decline of populations of species such as the burbot and white sturgeon.
The tribe’s conservation aquaculture program for white sturgeon is being implemented to reverse population declines and rebuild a population with demographic and genetic characteristics to ultimately become sustainable and resilient. A new hatchery has been proposed to both expand white sturgeon production, and begin burbot culturing on a larger scale than be done at the UI laboratory.