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

High variability in the April surveys may have been due to differences in the distance to
natal streams. For example, sites in the northeast corner of the lake near the mouth of Quinault
River appeared to have a higher abundance of Chinook salmon than other sites. Adjusting the
counts of Chinook salmon based on distance to natal streams would be difficult because there are
several natal streams spread around the east and south shoreline of the lake. In June, Chinook
salmon were probably well distributed around the lake and distance to the natal stream probably
had little influence on their abundance.
The abundance of Chinook salmon at emergent vegetation sites was highly variable.
Much of the variability appeared to be due to the substrate type and bottom slope. Sites with
sand and gravel substrates (hard substrates) tended to have a higher abundance (1.5 times higher
in April and 21 times higher in June) than emergent sites with silt and mud (soft substrates).
Areas with soft substrates also had a more gradual slope than areas with hard substrates. In 2001
and 2002, we made some preliminary observations on the use of soft substrates (silt and mud) by
juvenile Chinook salmon in Lake Washington (Tabor and Piaskowski 2002; Tabor et al. 2004b),
which suggested that they tend to avoid this substrate type. Results from surveys at Beer Sheva
Park provided further evidence that Chinook salmon do not extensively use soft substrates. The
reasons why soft substrates are avoided is unclear. We hypothesized that Chinook salmon may
avoid soft substrates in Lake Washington because these areas may have a higher density of
predators such as largemouth bass and brown bullhead. However, in Lake Quinault these
predators do not occur. Soft substrates also appear to have a higher density of macrophytes than
other substrate types and Chinook salmon may prefer a more open environment. Other possible
explanations include competition with threespine stickleback, which were predominantly found
in emergent vegetation sites with soft substrate. Other potential competitors, including speckled
dace and juvenile coho salmon, were also common in these sites. Also, the soft substrate sites
appear to often have higher turbidity than other sites which could reduce foraging success of
juvenile Chinook salmon.
In comparing fish abundance, we assumed that Chinook salmon could be observed
equally between the different habitat types. However, it is certainly possible that there was some
degree of bias. The distance at which a fish will react to a potential predator (reactive distance)
may be much longer in open areas than in complex habitats such as LWD and emergent
vegetation sites (Grant and Noakes 1987). Alternatively, fish can be difficult to observe in
complex habitats because they can easily hide from the observer. Additionally, emergent
vegetation sites with soft substrates appeared to have higher turbidity from wave action and/or
common carp activity, which may also have reduced our ability to observe juvenile Chinook
salmon. Some additional sampling techniques such as beach seining could be employed to
confirm the results but other techniques may also have some bias between habitats types.
Although we did not document a strong preference for LWD or emergent vegetation in
Lake Quinault, these habitats may still be more beneficial than open beach habitat if survival
rates are higher in structurally complex habitats. The addition of LWD or emergent vegetation
adds structural complexity and reduces the foraging ability of predators (Glass 1971). Research
in warm-water systems has been found that structural complexity is important for survival of
many species of juvenile freshwater fishes (Savino and Stein 1982; Werner and Hall 1988).
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