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Montana Ecological Services Field Office

585 Shepard Way, Suite 1 • Helena, Montana 59601 • 406-449-5225 • (FAX) 406-449-5339

 

 

Fisheries Applied Research and Technical Assistance

 

Kalispell Field Office

 

Experimental suppression of lake trout to support bull trout recovery in western Montana lakes

Reproducing lake trout populations, established either by natural invasion (i.e., migration from other connected waters) or illegal introduction (i.e., “bucket biology”), have increasingly presented a major obstacle to bull trout recovery efforts in western Montana.  Bull trout (Salvelinus confluentus) and lake trout (Salvelinus namaycush) are closely related species (same genus in the char complex) and while hybridization between the two is unlikely in the wild, there are strong competitive and predatory interactions between them (Martinez et al. 2009).  In the Flathead River drainage over two dozen natural lakes are home to native bull trout populations that have existed since the Wisconsonian glaciation, about 10,000 years ago.  Today, bull trout persistence is threatened in fully half of these waters, including all of the largest lakes (i.e., eight over 1,000 acres in size) and most of the medium sized lakes as well.  Less than 3% of the historic bull trout habitat (roughly 147,000 surface acres) in the Flathead watershed is positioned upstream of barriers where bull trout populations are considered stable, secure and isolated from invasion. 

Large male bull trout removed from gillnet and released alive back into Swan Lake

Photo Credit: Wade Fredenberg/USFWS

Large male bull trout removed from gillnet

and released alive back into Swan Lake

Graduate Research Assistant Ben Cox holding a large male lake trout in pre-spawning condition, captured from Swan Lake

Photo Credit: Wade Fredenberg/USFWS

Graduate Research Assistant Ben Cox holding a large male lake

trout in pre-spawning condition, captured from Swan Lake

Lake trout have several competitive advantages over bull trout. These advantages include longevity - lake trout may live upwards of 30 years while bull trout typically live less than 15; annual spawning producing large numbers of eggs, which exhibit high rates of survival, especially in lakes where nonnative Mysis shrimp and kokanee were also introduced; and the ability to compete with bull trout for food and space in the lake habitat where the lake trout spend nearly all their time.  Bull trout, on the other hand, must undergo arduous and sometimes long (up to 150 mile) spawning migrations and bull trout egg and juvenile survival is dependent to a large extent on the quantity and quality of available spawning and rearing habitat; some of which has been blocked off or impaired by human activities in many of the intensively managed watersheds.

Juvenile lake trout entangled in a gillnet and being removed from Swan Lake

Photo Credit: Daily Inter Lake

Juvenile lake trout entangled in a gillnet

and being removed from Swan Lake

Contract gillnetting crew removing small lake trout from Swan Lake gillnet for transfer to the Flathead Food Bank

Photo Credit: Wade Fredenberg/USFWS

Contract gillnetting crew removing small lake trout from

Swan Lake gillnet for transfer to the Flathead Food Bank

The Service has identified competitive interaction with nonnative fish as a very high priority for bull trout recovery and research initiatives and is actively supporting several experimental lake trout suppression projects out of our Kalispell suboffice.  The general goal is to determine whether we can selectively remove lake trout by targeted gillnetting at a high enough rate to keep lake trout populations in check.  Keys to success of the program are to remove a large proportion of the subadult lake trout (so that limited numbers will reach maturity) and then systematically target adult lake trout to cause a longer term reduction in the ongoing rate of reproduction.  All this must be accomplished while limiting inadvertent bycatch of bull trout in the nets.  Ongoing projects where the Service and our partners are attempting to suppress lake trout include Swan Lake and Quartz Lake. 

Lake trout captured alive in Swan Lake and about to be prepped for surgical implant of a sonic tag

Photo Credit: Wade Fredenberg/USFWS

Lake trout captured alive in Swan Lake and about

to be prepped for surgical implant of a sonic tag

 

Incision being made in body cavity of large lake trout for insertion of sonic tag to facilitate tracking.  The incision was subsequently sutured and the fish was

Photo Credit: Wade Fredenberg/USFWS

Incision being made in body cavity of large lake trout for insertion of sonic tag to facilitate tracking.  The incision was subsequently sutured and the fish was

released back into Swan Lake and tracked to its spawning grounds

 

In Swan Lake, a broad coalition of Federal, State, academic and private partners have funded and guided efforts to remove nearly 10,000 lake trout by commercial scale gillnetting in 2008 and 2009.  The resulting catch is believed to constitute over half the lake trout population in Swan Lake (based on a depletion estimate), which has grown dramatically since lake trout were first detected only a decade ago.  Sonic transmitters implanted in adult male lake trout have been used to track the spawners and then deploy targeted netting to remove both mature males and egg-bearing females from the spawning grounds, which are concentrated in select areas of coarse lakebed rubble.  To date, bull trout bycatch has been acceptably low.  Progress reports on this effort are available.

Wade Fredenberg with subadult bull trout captured by angling for purposes of genetic sampling from Quartz Lake in Glacier National Park

Photo Credit: C. Guy/USGS

Wade Fredenberg with subadult bull trout captured by angling for

purposes of genetic sampling from Quartz Lake in Glacier National Park

Adult bull trout captured by angling for purposes of genetic sampling from Quartz Lake in Glacier National Park

Photo Credit: C. Guy/USGS

Adult bull trout captured by angling for purposes of

genetic sampling from Quartz Lake in Glacier National Park

A second ongoing project involves a very similar study approach in Quartz Lake in Glacier National Park.  Lake trout were first detected in Quartz Lake in 2005, jeopardizing one of the last intact native aquatic species complexes in large lakes in the Flathead (Fredenberg et al. 2007).  In this case, the challenge is made even more difficult because the lake is accessible only by several miles of hiking trail.  A partnership between USGS, Glacier National Park, and the Service resulted in gill net removal of over 500 lake trout in 2009, after a motorboat was helicoptered in to facilitate the netting.  Because the lake is manageably sized (869 acres), it is hoped that early intervention will stave off the decline of bull trout that has occurred in similar waters (Fredenberg 2002).

Funding and Collaboration:  U.S. Fish and Wildlife Service, Region 6; Montana Fish Wildlife and Parks; Montana Department of Natural Resources and Conservation; Montana State University; Montana Trout Unlimited; U.S. Forest Service; Confederated Salish and Kootenai Tribes; Glacier National Park; U.S. Geological Survey.

Related Publications:

Fredenberg, W.  2002.  Further evidence that lake trout displace bull trout in mountain lakes.  Intermountain Journal of Sciences 8 (3): 143-152. (pdf).

Fredenberg, W.A., M.H. Meeuwig and C.S. Guy.  2007.  Action Plan to Conserve Bull Trout in Glacier National Park, Montana.  U.S. Fish and Wildlife Service, Kalispell, Montana.  (pdf).

Martinez, P.J., P.E. Bigelow, M.A. Deleray, W.A. Fredenberg, B.S. Hansen, N.J. Horner, S.K. Lehr, R.W. Shneidervin, S.A. Tolentino and A.E. Viola.  2009.  Western Lake Trout Woes.  Fisheries 34(9), September 2009.  (pdf).

Swan Valley Bull Trout Working Group.  2007 progress report.  (pdf).

Swan Valley Bull Trout Working Group.  2008 progress report.  (pdf).

 

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