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Fishery Bulletin 88(4), 1990 



winter annulus or spawning check) after initial ocean 

 entrance ("repeat spawners," Table 5). SLx of these had 

 apparently made one previous migration from the 

 ocean to freshwater, and two had made two previous 

 trips to freshwater. All of these fish measured 335- 

 380 mm FL except for one 279 mm FL fish. Half of 

 the repeat spawners had first entered the ocean after 

 one winter in freshwater (age 1.). Seven of the eight 

 prior spawners were collected in May or Jime, probably 

 soon after reentering the ocean. 



All juvenile steelhead caught in the ocean were in 

 their first ocean summer (age .0). Of the 89 steelhead 

 that had readable scales, 60%, 30%, and 10% were ages 

 1.0, 2.0 and 3.0, respectively (Table 5). Ten of 11 

 steelhead caught with clipped adipose fins, probably 

 denoting hatchery origin, were age 1.0. Since most wild 

 steelhead enter the ocean after two or three winters 

 in freshwater and most hatchery steelhead after only 

 one winter (Chapman 1958, Withler 1966, Pauley et 

 al. 1986), the majority of fish we caught were probably 

 of hatchery origin. 



Length ranges were broad for both cutthroat trout 

 and steelhead during each month (1981-85 combined, 

 Fig. 2). This may have resulted from variable size and 

 age of smolts entering the ocean (Loch 1982, Dawley 



et al. 1982, Bottom et al. 1984, Ward and Slaney 1988) 

 or variable growth rates. During downstream migra- 

 tion, the length ranges of individual hatchery groups 

 of steelhead smolts can be very broad. For example, 

 Dawley et al. (1986) found length ranges of 150-270 

 mm FL and 110-240 mm FL for two groups sampled 

 in the upper Columbia River estuary. 



Back-calculated length at time of ocean entry of cut- 

 throat trout averaged 241 mm FL, but was quite 

 variable (SD 38 mm, n = 101, repeat spawners ex- 

 cluded). Age 3.0 fish tended to be larger at time of first 

 ocean entry than younger fish or age 4.0 fish (average 

 back-calcidated FL at ocean entry = 231, 239, 264, and 

 244 mm FL for age 1.0, 2.0, 3.0, and 4.0 fish, respec- 

 tively). Our average back-calculated lengths at ocean 

 entry for cutthroat trout caught at sea were larger than 

 those back-calculated by Giger (1972) for wild cutthroat 

 of the same age from the Alsea, Nestucca, and Siuslaw 

 Rivers (239 vs. 210 and 264 vs. 239 mm FL for age 

 2.0 and 3.0 fish, respectively). However, the mean 

 length at ocean entry estimated by Giger for all fresh- 

 water age groups and for all three river systems com- 

 bined (233 mm FL) by Giger was fairly close to our 

 average (241 mm FL). 



