Abstract.- Coastal cutthroat 

 trout and steelhead, which are sym- 

 patric over much of their range along 

 the Pacific coast of North America, 

 have different behaviors in both 

 freshwater and the ocean. Juveniles 

 of both species were caught in purse 

 seines off the Oregon and Washing- 

 ton coasts during the early summer, 

 sometimes over 46 km offshore. How- 

 ever, both species were absent from 

 catches in September. Cutthroat ap- 

 parently returned to freshwater, 

 whereas steelhead migrated far off- 

 shore during late summer. Ocean 

 growth rates of smolts of both trouts 

 were similar, about 1 mm per day; 

 but since cutthroat spend little time 

 in the ocean, they are small at matur- 

 ity. This is possibly an adaptation 

 related to spawning short distances 

 from the ocean or in small trilaitaries 

 upstream of the spawning and rear- 

 ing habitats of other anadromous 

 salmonids. Cutthroat trout fed pri- 

 marily on fishes, but steelhead had 

 a more varied diet in coastal waters, 

 consuming fishes but also euphau- 

 siids and other crustaceans. 



Distribution and Biology 

 of Juvenile Cutthroat Trout 

 Oncorhynchus clarki clarki 

 and Steelhead O. mykiss 

 in Coastal Waters off 

 Oregon and Washington 



William G. Pearcy 



College of Oceanography, Oregon State University 

 Corvallis, Oregon 97331 



Richard D. Brodeur 



Fisheries Research Institute. University of U/ashington, Seattle, Washington 98195 

 Present address Pacific Biological Station. Department of Fisheries and Oceans 

 Nanaimo, B C . Canada V9R 5K6 



Joseph P. Fisher 



College of Oceanography, Oregon State University 

 Corvallis. Oregon 97331 



Manuscript accepted 16 May 1990. 

 Fishery Bulletin, U.S. 88:697-711. 



Two species of anadromous trout are 

 native to the Pacific coast drainages 

 of North America: Oncorhynchus c. 

 clarki (formerly Salmo c. clarki), the 

 coastal cutthroat trout, and 0. my- 

 kiss (formerly Salmo gairdneri and 

 5. mykiss), the steelhead and Kam- 

 chatkan trout (Smith and Stearley 

 1989). The coastal cutthroat trout 

 ranges from northern California to 

 southeastern Alaska. The native 

 range of the steelhead trout was 

 from the Alaska Peninsula to Baja 

 but now is found only as far south as 

 central California (Carl et al. 1959, 

 MacCrimmon 1971. Scott and Cross- 

 man 1973). 



Because these two trout species are 

 sympatric over much of their range 

 (Scott and Crossman 1973, Behnke 

 1979) behavioral and ecological dif- 

 ferences are of special interest. 

 Coastal cutthroat select small tribu- 

 taries for spawning, rarely over 160 

 km inland, whereas steelhead prefer 

 larger streams and sometimes mi- 

 grate long distances from the ocean. 

 Coastal cutthroat usually spawn 



slightly earlier in the year (January- 

 March) than steelhead (February- 

 April) (Needham and Gard 1959, 

 Withler 1966, Hartman and Gill 1968, 

 Scott and Crossman 1973, Johnston 

 1982). These differences in location 

 and time of spawning apparently help 

 maintain reproductive isolation be- 

 tween these species (Needham and 

 Gard 1959, Trotter 1989). 



Anadromous wild stocks of both 

 species of trout usually spend 2-4 

 years in freshwater before smoltifica- 

 tion and downstream migration to 

 the ocean, while hatchery stocks com- 

 monly migrate to the sea after one 

 year in freshwater. Downstream 

 migrations of smolts of both species 

 usually peak in April or May (Chap- 

 man 1958, Lowry 1965, Withler 

 1966, Armstrong i971, Giger 1972, 

 Sutherland 1973, Okazaki 1984, 

 Dawiey et al. 1985, Loch and Miller 

 1988) or in late May or early June in 

 Alaska (Armstrong 1971). 



Our knowledge of the marine life 

 history and ecology of steelhead and 

 cutthroat trout is meager. In this 



697 



