Vertical and horizontal movements of 

 adult Chinook salmon Oncorhynchus 

 tshawytscha in the Columbia River 

 estuary 



Alan F. Olson 



School of Fisheries WH- 1 0, University of Washington 

 Seattle, Washington 98195 



Present address: EA Engineering, Science and Technology Inc., 

 8520 1 54th Ave. NE, Redmond, Washington 98052 



Thomas P. Quinn 



School of Fisheries WH-1 0, University of Washington 

 Seattle. Washington 98195 



Maturing salmon leave oceanic feed- 

 ing grounds and migrate towards 

 their natal rivers, converging on 

 coastal and estuarine waters. Al- 

 though the passage through an es- 

 tuary represents a physical and 

 physiological milestone during the 

 homing migration of salmon and is 

 often a period of heavy commercial 

 and sport harvest, relatively little 

 is known about how oceanographic 

 processes might affect the distribu- 

 tion of salmon. Estuaries are tran- 

 sition zones between coastal and 

 riverine waters, and are areas of 

 rapidly changing temperature, sa- 

 linity, and current regimes which 

 may present migrating fish with 

 osmo- and thermoregulatory chal- 

 lenges. Furthermore, estuaries may 

 also represent a transition zone 

 for the orientation mechanisms 

 salmon use to find their natal 

 stream (McKeown 1984). 



Several investigators have ob- 

 served the horizontal movements 

 of Atlantic salmon Salmo salar 

 (Stasko 1975), sockeye salmon On- 

 corhynchus nerka (Groot et al. 

 1975), and chinook salmon 0. 

 tshawytscha (Fujioka 1970) in es- 

 tuaries, and observed both passive 

 and active movements with and into 

 tidal currents. More recent track- 



ing studies of maturing Atlantic 

 salmon, sockeye salmon, chum 

 salmon O. keta, and steelhead trout 

 O. mykiss in coastal waters have 

 demonstrated that their vertical 

 movements may be related to the 

 local vertical stratification of the 

 water column (Westerberg 1982, 

 Soeda et al. 1987, Quinn et al. 1989, 

 Ruggerone et al. 1990). No studies 

 are presently available which de- 

 scribe both the vertical and hori- 

 zontal movements of salmon within 

 an estuary. 



The following study was designed 

 to describe the short-term move- 

 ments of adult chinook salmon in 

 the Columbia River estuary outfit- 

 ted with pressure-sensitive ultra- 

 sonic tags to (1) relate these move- 

 ments to tidal currents and the 

 temperature and salinity structure 

 of the water column, and (2) exam- 

 ine how these movements might be 

 explained by their physiology and 

 the need for orientating clues. 



Materials and methods 



Study site description 



The Columbia River has a large es- 

 tuary with tidal influence extend- 

 ing approximately 161 km upriver 



from the mouth, although salt in- 

 trusion extends no more than 48 km 

 upriver along the bottom (Si- 

 menstad et al. 1984). Average 

 monthly river flows from 1969 to 

 1982 were 7460 mVs with a range 

 of 4070 m 3 /s in September to 

 10,530 m 3 /s in June (Simenstad et 

 al. 1984). This estuary has mixed 

 semidiurnal tides; that is, each tidal 

 day has two high and two low tides 

 of unequal size (Jay 1984). The 

 mean tidal range (mean high water 

 to mean low water) measured over 

 138 tides in 1958 was 2.31m at 

 North Jetty (Fig. 1; Jay 1984). 



Ultrasonic telemetry 



Chinook salmon were captured dur- 

 ing the morning of each tracking 

 day with short (~5min) drifts us- 

 ing 90-180 m of 21cm stretched- 

 mesh commercial gillnet (-12 m in 

 depth) which fished the entire wa- 

 ter column. When a fish was de- 

 tected, the net was immediately re- 

 trieved, and the fish removed and 

 placed in a 100 L cooler filled with 

 surface water. If more than one 

 chinook was captured, one was se- 

 lected for tracking based on scale 

 retention, lack of scars, and gen- 

 eral activity level. Total length was 

 measured to the nearest cm, and a 

 numbered disc tag was attached be- 

 low the dorsal fin. A pressure- 

 sensitive (74 mm long X 16 mm in 

 diameter) ultrasonic transmitter 

 (Vemco Ltd.), weighing 13 g in wa- 

 ter and calibrated within ±1 m to a 

 conductivity/temperature/depth 

 probe (CTD; InterOcean model 513) 

 prior to the track, was inserted into 

 the stomach of the unanesthetized 

 fish. The fish was placed in the 

 boat's partially-filled watertight fish 

 locker (2. 5x 1.5x0.5 m) for recovery 

 (-30-45 min). The holding tank al- 

 lowed the fish to reach the surface, 

 gulp air, and inflate its swim- 

 bladder. All fish were captured in 



Manuscript accepted 15 September 1992. 

 Fishery Bulletin, U.S. 91:171-178 (1993). 



171 



