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

TABLE 10.—Diet composition of juvenile Chinook salmon at the mouth of May Creek, 2004 under two
streamflow conditions. Base streamflow samples were collected on March 31 and April 1 and the high
streamflow samples were collected on March 26. n = the number of stomach samples analyzed; the range
of Chinook salmon lengths is also given; %N = percent number; %O = percent occurrence; %W = percent
weight; %IRI = percent index of relative importance.
Base flow
High flow
n = 10, range = 40-64 mm FL n = 10, range = 51-62 mm FL
Prey group %N %O %W %IRI %N %O %W %IRI
Insecta
Diptera
Chironomid pupae and adults 62.7 100 79.7 85.6 56.7 100 61.2 70.1
Chironomid larvae 3.7 40 1.6 1.3 17.9 70 16.0 14.1
Other aquatic diptera 0 0 0 0 2.2 30 1.8 0.7
Ephemeroptera 1.5 20 1.0 0.3 5.2 50 4.6 2.9
Collembola 4.5 30 0.8 1.0 2.2 20 0.5 0.3
Other aquatic insects 0.7 10 4.6 0.3 3.0 30 4.3 1.3
Homoptera (Aphididae) 0 0 0 0 0.7 10 0.8 0.1
Other terrestrial insects 0 0 0 0 0 0 0 0
Crustacea
Cladocera - Daphnia 0 0 0 0 0 0 0 0
Other crustaceans 0.7 10 0.3 0.1 0.7 10 0.2 0.1
Hydrachnida 0 0 0 0 0 0 0 0
Oligochaeta 0 0 0 0 8.2 90 6.1 7.7
Other 26.1 50 11.9 11.4 3.0 60 4.4 2.7
The diet at the mouth of Taylor Creek during high streamflow conditions was
significantly different than the lakeshore on the same date as well as Taylor Creek during
base flow conditions (Table 11). Chironomid larvae were the most important prey item
and represented approximately half of the prey items consumed. Other prey items
included chironomid pupae and adults, oligochaetes, springtails, and mayflies. The diet
breath index was 4.09, which was higher than any other creek mouth or lake sample.
Supplemental surveys of Kennydale Creek and Taylor Creek were conducted on
April 20, 2004. Chinook salmon were also collected at a lakeshore reference site, north
Gene Coulon Park. At the mouth of Taylor Creek, little else was present in the diet
except chironomid pupae and adults (97% by weight). Chironomid pupae and adults
were also the dominant prey item at the mouth of Kennydale Creek (58% by weight) and
the lakeshore reference site (83% by weight). However unlike Taylor Creek, aphids
made up a substantial part of the diet (Kennydale Creek, 25% by weight; lakeshore, 7%
by weight).
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