Deschutes River in north central Oregon (Figure 

 1). The Deschutes River drains approximately 

 10,400 square miles, or nearly 11% of the land area 

 of Oregon. Its western tributaries stem from the 

 Cascade Mountains, while eastern tributaries 

 drain Oregon's high plateau. Regulated river flows 

 below Pelton Dam average from 3,000 to 7,100 cfs. 

 Important sport fish in the area include resident 

 rainbow trout, summer steelhead trout, and 

 Chinook salmon, 0. tshawytscha, (Montgomery 

 1971). 



Collection of Samples 



Otoliths were obtained from adult (>200 mm 

 fork length [FL]) rainbow and steelhead (n = 101) 



COLUMBIA RIVER 



LOCKIT 



PELTON DAM 



Figure l.-Map of study area on the lower 100 miles of the 

 Deschutes River, Oreg. 



sampled during routine Oregon Wildlife Commis- 

 sion creel censuses at Webb's access road (at Buck 

 Hollow Creek) and near Maupin (Figure 1) during 

 August and September 1971 and 1972. Otoliths 

 were removed with a punch described by McKern 

 and Horton (1970). Each fish was measured (FL) 

 and scales (ca. 20) were removed from an area 

 below the origin of the dorsal fin and just above the 

 lateral line. Race was determined from a com- 

 bination of coloration, relative size, and analysis of 

 scales (Maher and Larkin 1954). In most cases sex 

 was determined from jaw conformation and oper- 

 cular coloration (steelhead only), and occasionally 

 from fisherman's observations if the fish had been 

 cleaned. To determine origin, we examined 

 steelhead for hatchery marks; hatchery-reared 

 rainbows were distinguished by worn or rounded 

 fins, excessive number of missing scales, and other 

 abnormalities. 



Other adult fish (w = 92) were collected by elec- 

 trofishing near Maupin, below Pelton Dam, and in 

 Bakeoven and Trout creeks (Figure 1) in April- 

 June 1971 and August 1972. Each fish was 

 measured (FL), and race, sex, and origin were de- 

 termined as above. Otoliths were removed by dis- 

 section. 



In January 1973, 52 steelhead fingerlings were 

 obtained from the stock of Deschutes River 

 steelhead reared at Wizard Falls Hatchery 

 (Oregon Wildlife Commission) on the Metolius 

 River. These fish represented a random assort- 

 ment of the offspring of ca. 150 females captured 

 below Pelton Dam. Fork lengths were measured, 

 and otoliths were removed by dissection. 



To determine body lengths of mature steelhead 

 trout and rainbow trout, specimens were obtained 

 by electrofishing in the lower Deschutes River in 

 1972. Fork lengths were measured, and race was 

 determined from hatchery marks or coloration 

 (migrating summer steelhead are more silvery 

 than resident rainbow). 



For determination of ova size, adult steelhead 

 were captured in late winter 1972 by trapping 

 below Pelton Dam and were held in tanks until 

 ripe. Twenty-two females were measured (FL), 

 and a sample of eggs (ca. 100) was collected from 

 each fish, fertilized, and allowed to water harden 

 8-22 h. From 20 to 60 eggs from each pairing were 

 then measured volumetrically (10"^ ml) in a 25-ml 

 burette. 



Rainbow trout were captured in spring 1972 by 

 electrofishing in the main stem of the Deschutes 

 River. Male-female pairs were individually 



655 



