ECOLOGY AND PRODUCTION OF JUVENILE SPRING 



CHINOOK SALMON, ONCORHYNCHUS TSHAWYTSCHA, 



IN A EUTROPHIC RESERVOIRn^ 



DUANE L. HiGLEY AND CaRL E. BOND^ 



ABSTRACT 



Juvenile spring chinook salmon, Oncorhynchiis tshawyischa, were reared in a central Oregon 

 reservoir of 7.5 hectare. The reservoir is strongly eutrophic, as shown by its heavy sedimen- 

 tation, summer stratification, and chemical qualities (total dissolved solids over 200 ppm, 

 total phosphorus to 0.4 ppm. and summer pH between 9 and 10). Surface water temperatures 

 ranged from 3° to 29°C. Salmon were apparently confined to the upper 3 m during the 

 summer because of low dissolved oxygen below this depth. In 1961, epilimnion conditions 

 of high pH, high temperatures, decreasing oxygen concentrations, and possibly algal toxins 

 caused condition loss and deaths among salmon. Fry planted in 1961 (75,300) and in 1962 

 (150,000) suffered first-summer mortalities in excess of 80%, primarily due to predation by 

 older salmon. Summer growth was rapid, but dependent on population densities. Coho 

 salmon, O. kisiitch, and chinook salmon remaining from a 1959 plant averaged 280 and 

 215 g after 30 mo. The 1961 year class averaged 62 g at 10 mo and 89 g at 22 mo. The 1962 

 year class averaged 22 g at 9 mo. Average condition factor values rose above 1.20 in the 

 summer. Net production by the 1961 year class was 159 kg/hectare in 1961 and 35.5 kg/ 

 hectare in 1962. The 1962 year class produced 170 kg/hectare in 1962. Potential December 

 yield of first-year salmon was 98 kg/hectare in 1961 and 73.5 kg/hectare in 1962. First-year 

 salmon ate primarily Entomostraca and chaoborid larvae. Apparently competition from the 

 1962 year class caused the 1961 year class to feed more on littoral and terrestrial forms and 

 to grow and produce less in their second year. Age class I and age class II salmon weighing 

 from 25 to 189 g emigrated via spillway outflows. In 1963, migrations occurred only at 

 temperatures above 10°C; this relationship was not observed in 1962. This reservoir, or 

 others with similar limnological conditions, cannot be recommended as a rearing site for 

 chinook salmon because of the severe summer conditions. 



Reduction in natural rearing sites available to 

 Pacific salmon, 0)}corhynchus spp., has led to a 

 search for ways of augmenting the smolt pro- 

 duction of various stream systems in the Pa- 

 cific Northwest. One possibility is to rear the 

 young salmon in impoundments where they 

 presumably would develop into naturally fed, 

 vigorous smolts. The smolts could then be re- 

 leased into nearby streams suitable for down- 

 stream migration. Various pond, lake, and 

 estuarial habitats have been utilized as rearing 



' Technical Paper No. 3439, Oregon Agricultural Ex- 

 perimental Station. 



- This research was supported by United Slates Depart- 

 ment of the Interior contracts 14-17-0001-374 and 14-17- 

 0001-544. 



3 Department of Fisheries and Wildlife, Oregon State 

 University, Corvallis, OR 97331. 



impoundments. This paper describes the results 

 of the rearing of chinook salmon, 0. tshawytscha 

 (Walbaum), of the spring race in Happy Valley 

 Reservoir, a eutrophic impoundment located 

 on the Warm Springs Indian Reservation in 

 central Oregon. The research correlated reser- 

 voir limnology with the growth, survival, food 

 habits, and migratorial tendencies of salmon 

 planted in the reservoir. The project period was 

 February 1961 to June 1963. 



The reservoir was the site of an earlier study 

 on the survival and growth of 30,000 coho salm- 

 on. O. kisutch (Walbaum), and 23,000 spring 

 chinook salmon, which were planted in January 

 1959. Shelton (pers. comm.) reported that growth 

 was rapid in both species, coho salmon averag- 

 ing 41 g and chinook salmon 32 g, after an 18-mo 



Manuscript accepted February 1973. 

 FISHERY BULLETIN: VOL. 71, NO. 3, 1973 



877 



