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

SUMMARY
In 2003 and 2004, we continued our assessment of juvenile Chinook salmon
(Oncorhynchus tshawytscha) habitat use in the nearshore areas of Lake Washington and
Lake Sammamish. Additional work was conducted in Lake Quinault to study habitat
features that are rare in the Lake Washington basin and serve as a more natural “reference
system” to Lake Washington. Juvenile Chinook salmon are found in Lake Washington
and Lake Sammamish between January and July, primarily in the littoral zone. Little is
known of their habitat use in lakes, as ocean-type Chinook salmon rarely occur in lakes
throughout their natural distribution. Research efforts in 2003 and 2004 focused on
juvenile Chinook salmon distribution, residence time and movements, shoreline structure
use (woody debris, overhanging vegetation, and emergent vegetation), depth distribution,
use of nonnatal tributaries, feeding at the mouths of tributaries, abundance at restoration
sites, and behavior of migrating smolts. Data on Chinook salmon habitat use were
collected primarily through snorkel surveys.
We repeatedly surveyed nine index sites in 2003 in south Lake Washington to
examine the temporal and spatial distribution of juvenile Chinook salmon. We surveyed
four sites on the east shoreline, four on the west shoreline, and one on Mercer Island.
Similar to 2002 results, the two sites closest to the Cedar River had substantially higher
densities of Chinook salmon from the beginning of February to the end of May than the
other seven sites. Overall, the abundance of Chinook salmon displayed a strong, negative
relationship with the shoreline distance from the mouth of the Cedar River to each site.
Juvenile Chinook salmon were present on Mercer Island on each survey date.
To better understand the residence time and movement patterns of juvenile
Chinook salmon, we conducted a marking study at Gene Coulon Park. Approximately
100 Chinook salmon (mean, 45 mm fork length) were collected from each of two sites
and each group was marked with a different color of dye and were later released where
they were captured. At 1, 7, 15 and 21 days after release, we snorkeled the entire
shoreline of Gene Coulon Park at night to look for marked fish. Results indicated many
Chinook salmon remain in a small area. We never found any Chinook salmon that had
moved more than 150 m. The median distance moved within the study area remained the
same from day 1 to day 21 but the number of marked fish observed declined
substantially. Therefore, it is possible that some fish moved outside of our survey area.
We continued to monitor restoration sites, both pre- and post-project, to help
determine if lake-shoreline habitat can be improved for juvenile Chinook salmon rearing.
A restoration project at Seward Park was completed in December 2001. The restoration
site as well as other Seward Park shoreline sites were surveyed in 2002-2004 and
compared to 2001 data. Numbers of juvenile Chinook salmon were generally low for
each year. Overall, we found no evidence of increased Chinook salmon use of the
Seward Park restoration site.
We also continued to collect baseline information at Beer Sheva Park and Martha
Washington Park. In addition, we also began collecting baseline data at Rainier Beach
Lake Park and Marina and the old Shuffleton Power Plant Outflow site. The boat ramp
area at Beer Sheva Park had high densities of Chinook salmon, and there appear to be
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