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

Observations were conducted primarily in the morning when the water was calm and fish
could be easily observed. On windy days, no observations could be conducted. Observations
were made by standing on the pier and observing schools of Chinook salmon as they swam near
the pier (Figure 49). The time each school was observed and the direction they are swimming
was noted. The size of each school of Chinook salmon was categorized as either small (< 50
fish), medium (50-100 fish), large (100-200 fish) or very large (> 200 fish). How Chinook
salmon responded to the pier was determined by estimating the depth of each school as the
approached the pier and the depth they were at as they past under or around the pier.
Results
Surface observations at the McClellan Pier were conducted once a week from May 21 to
July 3 in 2003 and May 19 to July 9 in 2004. During the first five surveys in 2003 (May 21 to
June 18), few juvenile salmonids were observed and no obvious movements were seen.
Similarly in 2004, few Chinook salmon were observed until June 16. On June 26, 2003 and June
16, 2004, large numbers of salmonids were observed moving along the shoreline. Based on fish
size and date, we assumed they were juvenile Chinook salmon. Snorkel surveys conducted in
2004 also indicated they were Chinook salmon. To better understand fish movements, we
conducted additional surface surveys during the period when Chinook salmon were abundant.
The timing of the migration appeared to coincide with the moon apogee, which has been also
suggested to be related to the passage of Chinook salmon smolts at the Ballard Locks (DeVries et
al. 2004).
When Chinook salmon were abundant at McClellan Pier, we took extended observations
to collect additional information on migrating Chinook salmon. In 2003, extended observations
were conducted twice (June 26 and July 1) and in 2004 they were conducted three times (June 16
to 18). On all five dates, observations were conducted from at least 0730 h to 1100 h (Figure
50). Peak number of schools was observed between 0800 h and 0830 h and the lowest
abundance was at the end of the survey between 1030 h and 1100 h. However, results of an
ANOVA test indicated there was no significant difference in abundance for any half hour period
between 0730 h and 1100 h. Additional observations were conducted if weather conditions and
personnel schedules permitted. On one date, June 16, 2004, we were able to make observations
from 0600 h to 1200 h (Figure 51). On this date, few schools of Chinook salmon were observed
before 0730 h and after 1100 h. Observations on other dates showed the same general trend;
little activity before 0700 h and a reduction in activity after 1100 h or 1200 h.
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