Goetz and Quinn: Behavioral thermoregulation by adult Oncorhynchus tshawytscha prior to spawning 
263 
ship canal to Lake Washington. Those migrating 
into the Lake Sammamish system spent, on aver¬ 
age, 7.9 d in Lake Washington, 7.5 d in the Sam¬ 
mamish River, and 4.8 d in Lake Sammamish. 
Individuals returning to the Cedar River spent 
on average 20.2 d in Lake Washington before 
ascending the river—the same total period as 
those moving through to Lake Sammamish. 
The proportion of total residence time in the 
estuary (lower and upper) was similar between 
years and tagging groups (mean: 47.1% [standard 
deviation (SD) 17.9], P=0.36; Table 3). However, 
there was an inverse relationship between time 
spent in the estuary and in Lake Washington (coef¬ 
ficient of correlation [r]=-0.350, df-91, P<0.001) 
that tended to conserve the overall transit time. 
This correlation was significant and stronger in 
2006 (r=-0.546) than in 2005 (/'=—0.118). 
Environmental conditions available 
to Chinook salmon 
The temperatures along the migration route were 
coolest in Puget Sound (range: 10-18°C), warmer 
in Salmon Bay (15.4-22.6°C) and the ship canal 
(17.3-22.5°C), and variable with depth in Lake 
Washington (8.5-22.5°C; Table 4). The estu¬ 
ary had a zone of dynamic short-term mixing of 
warm fresh water (20-23°C) and colder salt water 
(12-15°C) environments. The large lock and a 
small area of the upper estuary had a halocline 
at about 10 m; the upper estuary’s halocline had 
warmer surface water in August than that of the 
large lock (19.5°C versus 15.5°C). The DO levels 
at lower depths (13-10 m) in the upper estuary 
ranged from 5.7 to 7.1 mg/L, whereas in Lake 
Washington DO concentration at similar depths 
ranged from 6.4 to 7.4 mg/L. 
The upper estuary was slightly warmer than 
Lake Washington (20.8°C versus 20.2°C) at 
depths from 2 to 10 m, and more so at 12 m (just 
above the typical thermocline depth: 19.6°C ver¬ 
sus 17.9°C; Table 4). In 2005, it was 1.3°C warmer 
than in 2006 at all depths above 12 m in the 
upper estuary and 0.4°C warmer in Lake Washington at 
depths above 10 m. Temperatures in the upper estuary 
were similar at depth between August and September in 
2005, whereas in 2006 temperatures were more than 2.0°C 
cooler in August than in September at each depth. Lake 
Washington temperatures in August at depths <10 m were 
slightly warmer in 2005 than in 2006, and temperatures 
were similar each year in September; in both years August 
was 1-2°C warmer than September. 
Depths and temperatures experienced by Chinook salmon 
The depths occupied by Chinook salmon varied by reach 
and were influenced by bottom depth and the presence 
of thermal stratification (Fig. 4; see also Goetz, 2016). 
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Lake 
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Sammamish 
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Figure 3 
Typical hourly temperatures by location for Chinook salmon (Onco¬ 
rhynchus tshawytscha) migrating from the upper estuary in the 
Lake Washington watershed, in western Washington, to their final 
capture location in (A) Cedar River and (B) Issaquah Creek during 
July-October in 2005 and 2006. 
occupied cooler temperatures in the late afternoon and 
evening, and rose in the water column to shallower depths 
during the rest of the 24-h period. 
The Chinook salmon reached the spawning grounds 
slightly faster in 2005 than in 2006 (mean: 34.1 and 36.0 d, 
respectively, F=6.5, P<0.01; Table 3), and fish tagged ear¬ 
lier in August were slower in 2005 and 2006 (mean: 41.5 
and 37.1 d, respectively) than those tagged later in both 
years (mean: 31.0 and 33.8 d, respectively). The salmon 
took longer to move through the lower estuary (from Puget 
Sound to Salmon Bay) in 2005 than in 2006 but moved 
through the upper estuary faster in 2005 than in 2006; 
therefore, the overall time was similar between years. 
Once they exited the upper estuary, Chinook salmon 
moved quickly (mean: 0.6 d) through the 10.8 km from the 
