Nearshore Habitat Use by Juvenile Chinook Salmon in Lentic ...

Discussion
Johns Creek.— Results from Johns Creek indicated that Chinook salmon extensively use
this nonnatal tributary from year to year. Several nonnatal tributaries of Lake Washington and
Lake Sammamish were surveyed in 2002 and the number of Chinook salmon found in Johns
Creek was higher than all the other tributaries combined. Johns Creek appears to be an ideal
nonnatal tributary because it has a low gradient, is a small- to medium-sized stream, and is close
to the natal system, the Cedar River. Preliminary results from Lake Quinault in 2004 indicate
there are also several nonnatal streams that are used by juvenile Chinook salmon. We plan to
conduct additional surveys of these streams in 2005 to identify important factors that influence
their use of these streams. In the lower part of the Fraser River, British Columbia, juvenile
Chinook salmon used nonnatal tributaries that had low gradients and had no fish barriers such as
waterfalls, culverts, bridge footings, or flood control gates (Murray and Rosenau 1989). The use
of the lower reaches of nonnatal tributaries by juvenile Chinook salmon has also been
documented in the upper Fraser River system in British Columbia (Scrivener et al. 1994), the
Taku River system in Alaska (Murphy et al. 1989) and the Umpqua River system in Oregon
(Scarnecchia and Roper 2000).
Based on the habitat use patterns of Johns Creek, a suitable stream for juvenile Chinook
salmon should have a wide variety of habitat features, which would take into account the change
in habitat use of Chinook salmon as they grow. Shallow, slow water habitats (< 0.35-m depth)
or glides were used extensively in February and early March. We also observed small Chinook
salmon in pocket water of riffles, thus using cobbles and small boulders in riffles might provide
additional rearing habitat. After late March, Chinook salmon were usually in deeper pools but
we did not observe them in pools greater than 0.9 m depth. Throughout the study period,
juvenile Chinook salmon appeared to often use overhead cover.
The density of Chinook salmon in the convergence pool was considerably lower than in
the upstream reach. Low density in the convergence pool may be due to a combination of
suboptimal habitat conditions and presence of other fish species. Much of the convergence pool
had riprap banks and there was little woody debris and little riparian vegetation to provide
overhanging cover. Potential predators of Chinook salmon, such as largemouth bass,
smallmouth bass, large trout, and prickly sculpin, were commonly observed in the convergence
pool, thus Chinook salmon may avoid this area. Besides predators, the convergence pool also
had large numbers of potential competitors (juvenile peamouth, juvenile sunfish, threespine
stickleback, and prickly sculpin), which could reduce the food available for Chinook salmon. In
the upstream reach, few other fish species were present and the habitat conditions appeared to be
better than the convergence pool.
Culvert Creek.— Although few Chinook salmon were present at Culvert Creek, it does
provide evidence that small creeks or seeps could be potential Chinook salmon rearing habitat.
The number observed at Culvert Creek in 2004 was higher than the number observed in 2002 in
much larger tributaries such as May Creek (Tabor et al. 2004b). Use of these small tributaries
has not been well documented; however, in the Nooksack River system, Chinook salmon fry
were frequently caught in several spring seeps and small tributaries but not along the river edge
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