TABLE 1 Temperature, Dissolved Gases, Spill and Total Water Flow (in Thousands of c.f.s.) at . 

 Lower Monumental and Little Goose Dams from April to August, 1974. Data obtained by biweekly 

 airplane flights and analyzed by staff in Seattle. 



17.4 salmonids causing a loss of 5.2 million finger- 

 lings if a population of 300,000 squawfish exists for 

 the stretch of the river between Ice Harbor to Little 

 Goose Dam. 



The effects of dissolved gas on squawfish had 

 been examined by Meekin and Turner (1974) and 

 Blahm (1974). Blahm's results indicate that squaw- 

 fish were more resistant than juvenile salmonids 

 when stressed with supersaturation. Meekin and 

 Turner indicated slightly less tolerance than sal- 

 monids and that predation ability was substantially 

 reduced when they were in supersaturated condi- 

 tions. We attempted to place specific values on the 

 dissolved gas tolerance of the squawfish, to substan- 

 tiate and enumerate changes in the predation rate, 

 and to discern if any correlations exist between 

 laboratory experiments and field observations. 



TECHNIQUES AND MATERIALS 



Squawfish for our laboratory experiment in 

 Seattle were captured in a Lake Merwin trap in- 

 stalled in the Palouse River arm at Lyons Ferry, 

 Washington. This unit was identical to those 

 described by Hamilton et al. (1970) in the Lake 

 Merwin study in the Lewis River. Purse seining at 

 Little Goose Dam was accomplished with a seine 

 15-ft deep and 525-ft long operated from a power- 

 driven barge similar to that described by Durkin 

 and Park (1969). This shallow net was employed 

 because of the depth limitations near the navigation 

 locks and spill gates where we concentrated much 

 of our effort. 



All squawfish were tagged with a Floy anchor 

 tag, FD 67®, and released. Besides the tag, some 

 were branded using the liquid nitrogen technique 

 described by Mighell (1969); none were fin-clipped 

 or operculum-perforated. 



We purse seined at Little Goose Dam tailrace 

 under the assumption that squawfish would be 



42 Bentley, Dawley, Newcomb 



moving upstream to potential spawning areas of 

 rip-rap dikes adjacent to the dam. In addition to 

 learning something of their movements, we wished 

 to gain some knowledge regarding the numbers of 

 squawfish in that section of the river. Also, purse 

 seining at the dam during and after spill might tell 

 us whether there would be any change in behavior 

 or response to high nitrogen levels. In this area, 

 seining began on April 24 and concluded on August 8. 

 Since we wished to tag and recover the fish in this 

 area of the dam, we did not sacrifice the fish for 

 stomach analysis but examined the stomachs by 

 firmly pressing the lower ventral area and working 

 forward to the pectoral area. 



Water samples were taken biweekly by air- 

 craft; dissolved gas values were determined in our 

 Seattle laboratory by techniques described by Ebel 

 (1969) and Beiningen and Ebel (1970). 



Six laboratory tests were conducted where dis- 

 solved gas concentrations averaged 126.1, 120.4, 

 117.2 and 99.8% of saturation of total dissolved gas 

 (T.D.C). Average variation from the desired test 

 concentration was ±1.1% of T.D.G. Test duration 

 was 12 days. Simultaneous replicates were made of 

 tests at 117, 110 and 100% saturation. 



All test tanks were 1.2 m in diameter with 

 water depths of 25 cm (hydrostatic compensation 

 0.025 atm of pressure, or about 2.5% of saturation 

 decrease). Water flow was maintained at 7.5 C/min 

 at 10° ± 1°C. Tests were conducted with about 

 10 fish per tank over 12 days starting April 17, 1974. 

 Mean size of the test fish at introduction was 364 mm 

 and 534 g. Test fish were starved for 16 days prior 

 to testing. A sample population was fed to deter- 

 mine the maximum weight of food an unstressed 

 fish might consume in a 2-week period. A mixed 

 diet of live steelhead (average size - 21 g, 80 mm) 

 and dead smelt (average size - 30 g, 170 mm) was 

 used. On the basis of food intake of the sample 



