This study began
in 1998 to assess salmonid distribution, relative abundance, genetic
characteristics (stock status and trends), and the condition of salmonid
habitats in the Walla Walla River Subbasin within Washington. Stream
flows in the Walla Walla Subbasin continue to show a general trend
that consists of a decline in discharge in late May or June, followed
by low summer flows and usually an increase in discharge in fall,
or later in winter.
Stream flows in
the mainstem Walla Walla River have shown substantial increases in
some areas in recent years. The increase is apparently associated
with a 2000 settlement agreement between the U.S. Fish and Wildlife
Service (USFWS) and the Irrigation Districts to leave minimum flows
in the Walla Walla River. We documented low flows in the fall in the
mainstem Walla Walla River that are far below the settlement agreement
flows. The low flows we documented of less than 15 cfs likely create
a severe limitation on salmonid survival, migration or use of this
portion of the river. Additional emphasis needs to be placed on maintaining
adequate stream flows in the fall, in addition to during summer and
late spring.
Stream temperatures
in 2006 in the Walla Walla Subbasin were similar to those in 2005.
Upper montane tributaries maintained maximum summer temperatures below
65°F, while sites in the middle and lower Touchet and Walla Walla
rivers frequently had daily maximum temperatures well above 68°F
(high enough to inhibit migration in adult and juvenile salmonids,
and to sharply reduce survival of their embryos and fry). We summarized
the water temperature data for several sites in the lower reaches
of the Walla Walla River, Mill Creek, Dry Creek and the Touchet River
and compared seven day maximum temperatures with thermal criteria
for unimpeded fish passage. We identified many sites and years with
apparent thermal passage impediments in the lower portions of each
of these stream systems. High temperature is possibly the most critical
physiological barrier to salmonids in the Walla Walla Subbasin, but
other factors (available water, turbidity or sediment deposition,
cover, lack of pools, etc.) also affect salmonid distribution, survival,
migration, and breeding success. Increased flows in the Walla Walla
River from the USFWS/Irrigation Districts settlement agreement have
not produced consistent improvements to water temperatures in the
settlement area within Washington, or to stream flows and water temperatures
downstream.
Rainbow/steelhead
trout (Oncorhynchus mykiss) represent the most common salmonid
in the subbasin. Other salmonids including; bull trout (Salvelinus
confluentus), chinook salmon (Oncorhynchus tshawytscha), and
mountain whitefish (Prosopium williamsoni) had low densities
and limited distribution throughout the subbasin. We began a detailed
review of all the fish sampling data WDFW has available from several
hundred sites since 1997 to examine distribution of rainbow/steelhead,
whitefish, bull trout, chinook, brown trout and lamprey. The data
summary provides an evaluation by stream reach of distribution and
relative abundance for these species. All these species, except rainbow/steelhead,
have fairly limited distribution within the Washington portion of
the basin. Rainbow/steelhead have widespread distribution, although
they are absent during summer in some of the portions of headwater
areas and in the lower reaches of the basin where water temperatures
are high.
Steelhead spawning
surveys were conducted in four streams in the Walla Walla Subbasin
in 2006. Surveyors found 46 redds on Mill Creek and only 9 redds in
the Coppei Creek system (both South Fork and mainstem) and none in
Yellowhawk Creek. Survey conditions were poor with high flows and
turbid conditions during the first part of the spawning season. Therefore,
the steelhead spawning surveys should be considered as minimum estimates.
Bull trout spawning surveys in the upper Touchet River tributaries
found a total of 46 redds and 12 live fish, which is a substantial
decrease from the previous year (74 redds and 51 live fish). We did
not survey any more than the Wolf Fork and North Fork in 2006, and
surveys began later than usual because of the approximately 110,000
acre Columbia Complex Fire and associated access restrictions. Spring
chinook spawning surveys were not conducted in portions of the Touchet
River in 2006, because few adults were observed at the adult trap
in Dayton, and no redds or adults were observed during bull trout
spawning surveys.
After many years
of collecting tissues from steelhead and bull trout, WDFW completed
genetic characterizations using microsatellite DNA analyses for steelhead
(as well as in the Tucannon River and at Lyons Ferry Hatchery) and
bull trout in the Walla Walla Basin. Results of the steelhead analysis
indicate that steelhead are quite genetically different in the Walla
Walla and Touchet Basins and that there is little evidence to suggest
hatchery introgression into the natural populations in the Walla Walla
Basin. Results of the bull trout analysis show statistically significant
genetic differences among migratory bull trout in the Walla Walla
River near Milton- Freewater, upper Mill Creek and the Touchet River
at Dayton. In addition, significant genetic differences were found
for juvenile bull trout collected from five spawning areas of the
upper Touchet River drainage.
Recommendations
for assessment activities in 2007 include:
1) Monitor habitat
conditions to develop an adequate baseline, improve values in the
Ecosystem Diagnosis and Treatment (EDT) model, and to monitor changes
that result from habitat improvements.
2) Continue
bull trout and steelhead spawning surveys, and emphasize improving
counts or estimates of returning adults to determine escapement
annually at key locations within the subbasin.
3) Continue,
and expand the compilation of fish distribution and relative abundance
for fish or other aquatic species, including other data sets from
CTUIR and others, as well as incorporation of GIS mapping of distribution
and abundance.
4) Identify
appropriate management units for bull trout based on genetic information
available from this project, and determine causes for declines of
bull trout in the Touchet River to prevent extirpation of these
groups of salmonids.
5) Work with
other managers in the Walla Walla Subbasin to compile fish and habitat
data to fill gaps, improve planning, and evaluate efforts to restore
salmonids in the subbasin.
6) Continue
to work with CTUIR and others to develop a comprehensive RM&E
plan for the subbasin.
