NOTE Olson and Quinn: Vertical and horizontal movements of adult Oncorhynchus tshawytscha 



173 



Results 



Eight chinook salmon were tracked in the Columbia 

 River estuary from 27 August to 5 September 1987, 

 resulting in 56:39 h of tracking time over more than 

 127 km (Table 1). Mean river flow over Bonneville Dam 

 during the study period was 2910 m'Vs (range 2370- 

 3430 m : Vs: Fish Passage Center, Corvallis OR). Secchi 

 disc measurements taken intermittently during all 

 tracks had a pooled average depth of 2.47m (range 

 1.43-4. 12m for individual tracks). In general, signal 

 reception in the estuary was good and no fish were 

 lost during the tracking period. Tracking of a fish was 

 terminated owing to danger of vessel stranding on 

 mudflats (Fish 1), high waves at the river entrance 

 sandbar (Fish 2,4,8), darkness (Fish 3), or fish move- 

 ment into the ocean (Fish 6,7). Only Fish 5 was fol- 

 lowed during periods of darkness (l:09h). Five of the 

 eight fish (Fish 2,5,6,7,8) had dark or dusky skin color, 

 indicative of lower-river stocks known as tules. Bright- 

 skinned fish (Fish 1,3,4) may have derived from either 

 tules or upriver brights. All upriver brights enter 

 the river with a more "oceanic" appearance and return 

 to spawning grounds and hatcheries primarily near 

 the Hanford Reach (Howell et al. 1984); however, 

 some tules also enter the river in bright ocean-type 

 condition. 



Horizontal movements 



Fish usually moved in the direction of the prevailing 

 tidal current, and reversals in direction and a milling/ 

 holding behavior were often associated with changing 

 tides (Fig. 1). The average ground speed (weighted by 

 the number of sampling intervals) for tracked fish was 



2.33 km/h (range 1.28-3. 17km/h for individual fish 

 (Table 1). Ground speeds are the resultant of two 

 vectors: velocities (speed and direction) of the tidal 

 current and of the tracked fish. When analyzed by 

 tidal stage, mean ground speeds for individual fish 

 ranged from 0.74 to 4.08 km/h (2.60 overall) during 

 ebbing tides, and 0.91 to 3.12 (2.04 overall) during 

 flood tides (Table 2). 



Two chinook salmon were recovered after the track- 

 ing period. Fish 2 was recaptured 14 d after release 

 during test fishing operations 93 km from the river 

 mouth, and Fish 7 was recaptured 9 d after release by 

 a sportsman about 80 km from the river mouth. These 

 fish had net travel rates of 6.0 and 7.8 km/d, respec- 

 tively, after release. 



Vertical movements 



Mean fish depth was 5.5 m, and mean water depth 

 beneath the boat was 13.4 m (Table 3). Vertical pro- 

 files of temperature and salinity indicated extremely 

 dynamic hydrographic regimes. Within a single track, 

 some profiles indicated nearly uniform temperatures 

 and salinities over all depths, while others revealed 

 strong haloclines and thermoclines. Vertical track maps 

 (Fig. 2), and fish-depth frequency distributions rela- 

 tive to mean temperature and salinity profiles (Fig. 3) 

 for Fish 4 and 5, show two observed patterns of verti- 

 cal movement: Some salmon swam in brackish sur- 

 face waters with large vertical gradients of salinity 

 and temperature and made occasional excursions into 

 uniform bottom waters (Fish 2,6,7,8), whereas others 

 demonstrated periods of swimming in the water col- 

 umn and near the bottom (Fish 1,3,4,5). Some vertical 

 track maps show fish that appear to be deeper than 



