The ESA (Threatened)
listing of the Columbia River Distinct Population Segment of bull
trout identified one of the major threats to the species as fragmentation
resulting from dams on over wintering habitats of migratory subpopulations
(Federal Register, 1998). At the time of listing, it appeared that
a migratory subgroup in the Tucannon River may have utilized the mainstem
Snake River for adult rearing on a seasonal basis (Underwood et al.,
1995). The occurrence of bull trout in the hydropower system had been
verified by a few incidental observations during sampling in Lower
Monumental Pool (Buchanan et al. 1997 citing Ward), and in the adult
passage facilities at Lower Monumental and Little Goose dams in the
early 1990s (Kleist, in litt. 1993). Prior to 2001, documentation
of fish movement past the adult fish counting windows at Lower Monumental
Dam and Little Goose Dam occurred during spring, summer, and fall,
but was suspended during winter months (November through March). The
FCRPS Biological Opinion (USFWS 2000) required the U. S. Army Corps
of Engineers (USACE) to provide data detailing the movement of bull
trout past the adult fish counting stations at Lower Monumental and
Little Goose Dams. This requirement prompted USACE to extend the collection
of adult fish passage data into the winter months (i.e., November
through March).
Time-lapse video
counting did not document the presence of bull trout at Lower Monumental
and Little Goose dams during the winter of 2003/2004 (Richards, pers.
comm., 2004). However, bull trout have been observed at the fish viewing
windows during spring and summer at both hydroelectric facilities
since records were kept in 2001 (Anglea, et. al., 2004). Additionally,
bull trout have been found in the adult/juvenile separator at the
juvenile fish facility at Little Goose Dam in 2004 and 2005. The origin
of these fish is unclear.
It remains unconfirmed
if bull trout from the Tucannon River frequently utilize the main
stem Snake River for rearing and foraging as observed in large rivers
in other Columbia Basin subpopulations (Elle 1995; Faler and Bair
1992; Kelly Ringell and DeLaVergne 2000 and 2001; Schriever and Schiff;
2003; Theisfeld et al. 1996; Underwood et al. 1995). If bull trout
originating from the Tucannon River migrate into the mainstem Snake
River, it is also unknown if they attempt to pass the existing hydro
facilities on a regular basis, or if the fishways are suitable for
bull trout passage.
The potential
for bull trout movements throughout the migratory corridor is high,
but from the standpoint of future delisting and requirements set forth
in the FCRPS Biological Opinion (USFWS 2000), the determination of
temporal and spatial distribution in the mainstem is crucial in developing
recovery actions, estimating “take”, and successful consultation
on system improvement actions. This project was designed to help meet
Reasonable and Prudent Measures, and Conservation Recommendations
associated with the Lower Snake River dams in the FCRPS Biological
Opinion, and to increase understanding of bull trout movements within
the Tucannon River drainage.
Rieman and McIntyre
(1993) describe unimpeded migratory corridors as important habitats
to the persistence and interaction of local populations. They also
indicate that disruption and/or modification of migratory corridors
can increase stress, reduce growth and survival, and potentially result
in the loss of migratory life-history types in a subpopulation. With
these factors in mind, the primary question to be answered is: Does
the existing hydropower system on the Lower Snake River limit the
capabilities of Tucannon River bull trout to complete their migratory
behavior, or are the current hydropower operations compatible with
recovery and conservation of the species? The secondary goal of the
project is to examine the movements and spatial/temporal distribution
of migratory bull trout within the Tucannon River and to determine
the proportion of migratory fish that leave the Tucannon River to
overwinter. The bull trout stock status in the Tucannon River is considered
healthy by the Washington Department of Fish and Wildlife (WDFW 1998),
but little is known about their migrations in the Tucannon and Snake
river subbasins. Martin et al. (1992) and Underwood et al. (1995)
studied the interactions of bull trout, steelhead, and Chinook salmon
in the Tucannon River during the early 1990’s. As part of this
larger study, there were 16 bull trout radiotagged and tracked from
July through November 1992. The authors indicated that 2 fish may
have entered the main stem Snake River by the last week of October,
but they were unable to verify these movements (Underwood et al. 1995).
The objectives
of this study are to:
1. Determine
the spatial distribution, migration timing, and movements of adult
migratory bull trout in the Tucannon and Snake rivers.
2. Determine
bull trout use and passage efficiency in fishways at Lower Snake
River dams.
3. Estimate
frequency of bull trout fall back at Lower Snake River dams.
4. Determine
if bull trout losses result from movements out of Lower Monumental
Pool.
The primary assumption
associated with the study is that the movements of radio-tagged bull
trout are not different from the movements of other bull trout in
the subgroup. This assumption is critical to the project as a whole.
The use of long life transmitters and tagging well before spawning
or major migrations should reduce the effects of tagging on fish behavior.
Martin et al. (1995) found that surgically implanted dummy transmitters
did not affect fish survival, growth, or gonad development in rainbow
trout held in captivity. Radio transmitters have been used in other
bull trout studies in recent years with good success (Elle 1995, Faler
and Bair 1992, Kelly Ringel and DeLaVergne 2000/2001, Schriever and
Schiff 2003, Underwood et al. 1995). Objectives 1, 2 and 4 have critical
assumptions, in part, associated with each of those objectives. In
order to determine distribution in the Snake River (Objective 1) and
passage efficiency (Objective 2), we must assume that a portion of
our group of radio-tagged bull trout will enter the Snake River and
at least attempt to pass through a fish ladder in the Lower Snake
River.
Likewise, in order
to estimate the extent of losses in Objective 4, there must be some
movement (upstream or downstream) of radio-tagged bull trout out of
Lower Monumental Pool and we also assume that radio transmission will
be adequate to track bull trout movements throughout the reservoirs.
