FOOD AND GROWTH PARAMETERS OF JUVENILE 



CHINOOK SALMON, ONCORHYNCHUS TSHAWYTSCHA, 



IN CENTRAL COLUMBIA RIVERA 



C. Dale Becker^ 



ABSTRACT 



Juvenile chinook salmon, Oncorhymhus i.\luiwyi.sclui, in the Hanford area of the free- 

 flowing central Columbia River, Wash., consume almost entirely adult and larval stages 

 of aquatic insects. Their diet is dominated by midges (Diptera: Chironomidae). By 

 numbers, adult midges provided 64 and 58% of the diet and larval midges 17 and 18% 

 of the diet, in 1968 and 1969, respectively. The families Hydropsychidae (Trichoptera 

 or caddisflies), Notonectidae (Hemiptera or true bugs), and Hypogastruridae (Collembola 

 or springtails) are of minor numerical importance with a combined utilization of 7% 

 in 1968 and 15% in 1969. 



Distinctive features of food and feeding activity of juvenile chinook salmon at Hanford 

 are fourfold: 1) the fish utilize relatively few insect groups, predominantly Chironomidae; 

 2) they depend largely upon autochthonous river organisms; 3) they select prey drifting, 

 floating, or swimming in the water; and 4) they are apparently habitat opportunists 

 to a large extent. Analyses were made of variations in diet and numbers of insects 

 consumed between six sampling stations distributed along a 38-km section of the river. 

 Data are provided on feeding intensity, fish lengths, length-weight relationships, and 

 coefficients of condition. Seasonal changes in river temperature and discharge, as well 

 as variations in regulated flow levels, are environmental features influencing feeding, 

 growth, and emigration of fish in the Hanford environs. 



Food habits of juvenile chinook salmon, On- 

 corhijnchns t.shawytscJia (Walbaum), have been 

 reported from various habitats including the 

 Sacramento River, Calif. (Rutter. 1904); lower 

 Sacramento-San Joaquin system, Calif. (Sasaki, 

 1966); lower Chehalis River and upper Grays 

 Harbor system, Wash. (Herrmann, 1970); 

 middle Willamette River, Oreg. (Breuser, 1954); 

 and tributaries of the central Columbia River, 

 Wash. (Chapman and Quistorff, 1938). Initial 

 observations on feeding bionomics of juvenile 

 chinook salmon in the central Columbia River 

 were conducted in 1968 (Becker, 1970a). The 

 study was expanded in 1969. The objectives 

 of this report are to present data based on 

 the more extensive 1969 investigation and 



'This study was supported by Contract AT(45-1)- 

 1830 with the United States Atomic Energy Commission. 



2 Ecosystems Department, Baltelle Memorial Institute, 

 Pacific Northwest Laboratories, Richland, WA 99352. 



Manuscript accepted November 1972. 

 FISHERY BULLETIN: VOL. 71, NO. 2, 1973. 



to discuss theoretically the influence of en- 

 vironmental features. 



The mainstem Columbia River above Bonne- 

 ville Dam has been altered during recent 

 decades into a nearly consecutive series of 

 artificial impoundments arising from hydro- 

 electric development. Only one section of the 

 main channel now survives in its natural, 

 free-flowing condition. This section extends 

 from Richland, Wash., some 93 km upriver 

 to Priest Rapids Dam, where it forms the 

 northern and northeastern boundaries of the 

 Atomic Energy Commission's Hanford Reser- 

 vation (Figure 1). 



Most spawning grounds for salmonids 

 throughout the mainstem Columbia River have 

 now been inundated by the reservoir complex 

 (Fulton, 1968). Maintenance of salmonid re- 

 sources is due largely to providing access 

 over otherwise impassable dams, propagating 

 young fish in hatcheries and spawning channels. 



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