HIGLEY and BOND: CHINOOK SALMON IN A RESERVOIR 



r-^° 



IB 22 

 JULY 



30 



14 IB 

 AUGUST 



22 26 30 



Figure 9. — Dissolved oxygen concentrations at 0.6, 1.8, 

 and 3 m (2, 6, and 10 feet) during July and August 1961. 

 Salmon typically inhabited water 1.2 to 1.8 m deep during 

 this period. Samples taken midday at station 1. 



Doudoroff (1960), who state that at 16.5° to 

 25.5°C, under controlled conditions, juvenile 

 Chinook salmon directly avoided oxygen con- 

 centrations of 4.5 mg/liter and below. 



Conditions in the upper 1.8 m of water were 

 sometimes marginal for survival of the salmon 

 because of 18° to 29°C temperatures (Figure 10), 

 varying oxygen concentrations, and other stres- 

 ses. Between 31 July and 3 August 1961, 65 

 dead salmon (50 of 1959 year class and 15 of 

 1961 year class) were collected at the water 

 surface. Fish broke water in obvious distress 

 at various hours of the day. At this time, a 

 heavy bloom of Apha)iizomeiioii was decompos- 

 ing, accompanied by declines in surface pH 

 (Figure 6) and oxygen concentrations (Figure 

 9). Oxygen concentrations remained at 5 to 8 

 mg/liter in the upper 1.5 m of water during a 

 24-h series taken 31 July-1 August. During the 

 die-off, daily temperature maxima were reach- 

 ing 23°C at 1.5 m (Figure 10). Brett (1956) 

 estimated that 25.1 °C is the upper lethal limit 

 for Chinook salmon acclimated to 20 °C. The 

 combination of low oxygen, high temperature, 

 high pH, and possibly algal toxins apparently 

 formed untenable conditions for some of the 

 fish. 



During the extreme conditions of midsummer 

 1961, the 0-age class salmon lost condition 

 (see later section on Condition). Herrmann, 

 Warren, and Doudoroff (1962) observed pro- 

 gressively lower food consumption and growth 

 rates among juvenile coho salmon held at 20°C 

 and exposed to decreasing oxygen concentra- 

 tions. The most rapid decline in these rates 



IB 22 



JULY 



10 14 



AUGUST 



IB 22 26 30 



Figure 10. — Daily maximum-minimum temperatures at 

 surface and at 1.5 m (3 feet) during July and August 1961. 

 Maxima at the surface exceeded the lethal limit (25.1°C) 

 for Chinook salmon fry, and reached 23 °C at 1.5 m. Data 

 from thermograph records for station 2. 



occurred at concentrations decreasing below 

 4 mg/liter and weight losses occurred at 2 

 mg/liter. Salmon in Happy Valley Reservoir, 

 on the whole, grew rapidly during the summer 

 despite occasionally critical conditions. They 

 surface-fed in the mornings and evenings in 

 water as warm as 21° to 23.5°C. Brett (1952) 

 also noted that his experimental salmon fry 

 would move up through strong temperature 

 gradients and into temperatures near their 

 lethal level to feed at the surface. 



During the summer, salmon generally con- 

 gregated along the dam face and in the south- 

 west corner. The reason for this is not known; 

 oxygen concentrations and temperatures were 

 similar to those in other areas of the reservoir. 

 However, when a freshet brought a cooler (and 

 probably more highly oxygenated) water mass 

 into the inlet, the salmon quickly congregated 

 there. On 14 August 1962, surface temperature 

 was 24.5°C in the lower reservoir and 19°C in 

 the inlet. The temperature difference soon dis- 

 appeared, but the salmon remained abundant 

 in the inlet until late September when fall 

 turnover began. 



The salmon were less frequently captured 

 and were more uniformly distributed about 

 the reservoir during the winter than in the 

 summer. No vertical limitation was evident. 

 Cold water caused no observed deaths, but 

 apparently reduced the activity of the fish, and 



883 



