Lake Bull Trout
the present size of the bull trout population within the Odell Lake Recovery
Unit is unknown, it appears to be quite small. Spawning by bull trout
of the Odell Lake Recovery Unit occurs only in the lower 0.8 km of Trapper
Creek, below a falls presumed to be a barrier. Numbers of redds observed
in Trapper Creek from 1996 through 2002 have ranged from one to 24. In
addition to genetic effects caused by small population size, primary threats
to the sustainability of these bull trout include limited spawning and
rearing habitat in all streams, hybridization with brook trout in upper
Trapper Creek, competition from other fish species, particularly lake
trout in Odell Lake, and superimposition of kokanee salmon (O. nerka)
redds on bull trout redds. The latter threat may be particularly detrimental
because of the large number of kokanee that spawn in lower Trapper Creek.
concerns of bull trout redd superimposition by bull trout,
the Native Fish Investigations Project has designed
1) Assess the impacts to bull trout reproduction caused by kokanee that
spawn at the same location, and
2) Develop acceptable methods to separate bull trout and kokanee that spawn in Trapper
Creek, Odell Lake.
first objective will address the concerns that kokanee redds superimposed
on bull trout redds will reduce the number of bull trout progeny. During
the spawning season, we will cap several undisturbed bull trout redds
and an equal number of redds superimposed with kokanee salmon redds. Emergent
fry will be captured, identified, and enumerated; statistical comparisons
of fry abundance will be made between both groups of redds. To adjust
for spawner fecundity, estimates of the size of females that make each
redd will be obtained visually. We intend to conduct these studies at Heising Springs on the Metolius River, which helps support one of the
healthiest bull trout populations in Oregon.
second objective addresses efforts to enhance the Odell Lake bull trout
population. Recently, managers installed a weir to block passage of kokanee
salmon to spawning areas in Trapper Creek; bull trout were captured and
placed upstream. This activity led to opposition by anglers supportive
of kokanee and loss of adult bull trout by an otter that invaded the trap.
Our intent is to help managers design and implement methods that 1) prevent
kokanee salmon from impacting bull trout redds in Trapper Creek, 2) enable
bull trout to move into and out of Trapper Creek without capture and handling,
and 3) enumerate bull trout spawning in Trapper Creek. Data collected
in Trapper Creek should help with design and implementation of methodologies
to separate the species during the spawning season.
Annual Reports and Publications:
Richardson, S.E., and S.E. Jacobs. 2010.
Lake Bull Trout.
Oregon Department of Fish and Wildlife, Annual Progress Report 2010, Corvallis.
Weeber, M.A., G.R. Giannico, and S.E. Jacobs. 2010. Effects of redd superimposition by introduced kokanee
on the spawning success of native bull trout. North American Journal of Fisheries Management 30:47-54.
Weeber M.A. 2007. Effects of
kokanee (Oncorhynchus nerka) redd superimposition on bull trout (Salvelinus
confluentus) reproductive success in the Deschutes River Basin,
Oregon. Masters Thesis. Oregon State University, Corvallis.
Weeber, M. 2006.
Effects of Kokanee redd superimposition on bull trout egg-to-fry
survival: Summary of initial findings. Oregon Department of
Fish and Wildlife Interim Report, Corvallis.
Moore,T. 2005. Trapper Creek
PIT tagging and mark-recapture population estimate, June 2005.
Oregon Department of Fish and Wildlife Interim Report, Corvallis.
A., T.G Wise and S. Jacobs. 2005.
and location of bull trout in the Odell Lake watershed and Heising
Spring of the Metolius River watershed, 2003-2004. Oregon
Department of Fish and Wildlife, Information Report