passed before alkalinity below the reservoirs 

 reached that of the inflowing water in August. 

 Again, the delaying effect of the reservoir is 

 aj^parent. 



POSSIBLE EFFECTS OF LIMNOLOGICAL 

 CONDITIONS ON SALMON 



The most important environmental factors that 

 could affect the migration, distribution, and sur- 

 vival of juvenile salmonids in Brownlee Reservoir 

 were water temperatures, dissolved oxygen 

 concentrations, and currents. 



Temperature tolerance ranges and temperature 

 preferences of juvenile salmon liave been deter- 

 mined by several authorities. Brett (1952) listed 

 maximum temperatures for survival of young 

 salmon between 23.8° and 25.1° C. Ferguson 

 (1958) placed the temperature preference for 

 Chinook salmon (Onrorhynr-hm ts'hawytsrhri) and 

 pink salmon {0. gorhmcha) at 11.7° C. Donaldson 

 and Foster (1941) concluded that young sockeye 

 salmon {0. nerka) fingerlings were barely able to 

 maintain themselves at 21.1° C. and could not tol- 

 erate water as high as 25.5° C. for more than a few 

 days. 



Ellis (1944), McKee (1952), and Fisher (1963) 

 discussed dissolved oxygen levels. Ellis stated that 

 dissolved oxygen content of not less than 5 p. p.m. 

 was favorable to a mixed fauna of food and game 

 fish of the "warm water type." McKee indicated 

 that a dissolved oxygen concentration of 3 p.p.m. 

 was minimal for fresh-water fishes. Fisher found 

 that oxygen levels were definitely correlated with 

 growth of coho salmon (0. hmdch). In general, 

 high dissolved oxygen concentrations increased 

 growth, and low levels retarded growth. 



The temperature and oxygen requirements for 

 salmonids were not always met in Brownlee Reser- 

 voir; at times the movement of salmonids was re- 

 stricted or perhaps seriously impaired. From late 

 July through September, high surface water tem- 

 peratures and low oxygen concentrations in the 

 hypolimnion limited the survival area to a layer 

 between 15.2 and 30.5 m., where temperatiires 

 ranged from 18.3° to 23.9° C. and oxygen fluctu- 

 ated between and 7 p.p.m. In some zones tempera- 

 tures ranged from 12.8° to 15.5° C, but these areas 

 were either completely void of oxygen or blocked 

 off by water masses with no oxygen. Thus, hori- 

 zontal as well as vertical distribution of salmonids 



was affected by temperature and oxygen. When 

 oxygen blocks were present in the upper reservoir 

 in late July, fish could have l)een forced up- or 

 down-reseivoir by serious oxygen depletion and 

 high temi>eratures. Growth and survival of indi- 

 viduals remaining in the reservoir during August 

 and September could have been reduced, espe- 

 cially in years when oxygen concentrations were 

 extremely low and temperatures rose to nearly 

 letlial levels. For example, oxygen and temperature 

 were at nnich more critical levels for salmonids 

 in August 1962 than in August 1963. 



Alkalinities, pH, and conductivities were within 

 acceptable limits for fish life, although conductiv- 

 ity and pH reached nearly critical levels at times. 

 Sulfate and alkalinity concentrations during most 

 of the year were suitable if not optimal for aquatic 

 life. McKee and Wolf (1963) stated that the 

 range in concentration of sulfate in U.S. waters 

 tliat supported good game fish was 11 to 90 p.p.m. 

 Tliey also stated that alkalinity, when caused al- 

 most entirely by bicarbonate, did not seem to hanu 

 aquatic life. Concentrations of sulfate in Brownlee 

 Reservoir fell within this range, and alkalinity 

 was primarily bicarbonate. 



Several authoi-s examined the relations of total 

 dissolved solids, total alkalinity, and conductivity 

 to productiHty: most of them found a positive 

 correlation. Northcote and Larkin (1956) indi- 

 cated, in their study of 100 British Columbia lakes, 

 that total dissolved solids were the most important 

 factor in determining the general level of produc- 

 ti\-ity. Lakes with the highest productivity had 

 total dissolved solids in excess of 100 p.p.m. At 

 the time of one study, the total dissolved solids of 

 Brownlee Reservoir were well in excess of 100 

 p.p.m. Even though sufficient nutrients were ap- 

 parently available for high productivity, critical 

 values of temperature and oxygen during mid- 

 summer tended to restrict the growth and move- 

 ment of salmonids in Brownlee Reservoir. 



Two of the diurnal studies showed variations 

 in temperature and oxygen concentrations that 

 probably influenced vertical movements of sal- 

 monids. Variations in temperature amounted to 

 1.65° and 2.2° C. in 2i4-hour periods during July 

 and August 1963, when variations in oxygen con- 

 centrations also were significant. Cooling of the 

 surface waters in the evening and early morning 

 may have enabled salmonids to move toward the 



332 



U.S. FISH AND WILDLIFE SERVICE 



