698 



Fishery Bulletin 88(4). 1990 



paper we describe the distribution and movements, age 

 and size distribution, sex ratios, and food habits of 

 juveniles of these species in coastal waters off Oregon 

 and Washington as determined by purse seine catches, 

 discuss the differences between these species, and 

 speculate on their adaptive significance. 



Methods 



Cutthroat trout and steelhead were captured in purse 

 seines in the northeastern Pacific Ocean during May- 

 September, 1980-85. Data from 1981-85, the years of 

 most extensive sampling, are the basis for most of this 

 paper (see Pearcy and Fisher 1988, for sampling de- 

 tails). A total of 992 quantitative seine sets were made 

 with a 457-495 m seine with 32-mm (stretch measure) 

 mesh that fished to depths of 20-65 m. Sets were made 

 along east-west transects off Oregon and Washington 

 (43°00'N to 48°21'N) at 9.3 km (5 n.mi.) intervals out 

 to about 50 km offshore (Fig. 1). During July 1984, we 

 sampled over a broader area, from northern Califor- 

 nia (40°32'N) to Vancouver Island (50°26'N). 



Trout were identified, measured (fork length, FL), 

 examined for marks, and either released or preserved 

 by freezing at sea. A total of 15 cutthroat and 8 steel- 

 head were tagged with Floy tags and released. In the 

 laboratory ashore, the preserved fish were measured, 

 weighed, scales were removed, stomachs excised, and 

 gonads were examined. 



Scales from cutthroat trout and steelhead were col- 

 lected from an area 1-3 scale rows above the lateral 

 line along the diagonal scale row from the insertion of 

 the dorsal fin (Clutter and Whitesel 1956). Scales were 

 mounted on gummed cards from which acetate impres- 

 sions were made. The impressions were magnified 

 88 X . All measurements were made in the anterior half 

 of the scale along an axis 20° ventrad to the long axis. 

 Ages of smolts at ocean entrance were estimated by 

 counting the bands of narrowly spaced or broken cir- 

 culi (interpreted as winter annuli) in the freshwater 

 growth zone of the scale. These freshwater ages are 

 estimates because occasionally "checks," which were 

 difficult to interpret, occurred in the freshwater gi'owth 

 zone and few scales from fish of known freshwater age 

 were available for comparison. The abrupt change from 

 relatively narrowly to widely spaced circuli indicated 

 the transition from freshwater to ocean growth. Subse- 

 quent zones of narrowly spaced circuli or resorption 

 on cutthroat trout scales were interpreted as evidence 

 of slow growth from reduced feeding or spawning in 

 freshwater [see Sumner (1962, 1972) and Loch and 

 Miller (1988) for scale interpretations and photo- 

 graphs]. All juvenile steelhead collected were in their 

 first summer in the ocean and had not yet spawned. 



125° 124° 



I I I Ml I I II I II ij^ 



WAATCH POINT 



SEA LION ROCK 



DESTRUCTION ISLAND 



QUINAULT RIVER 



GRAYS HARBOR 



WILLAPA BAY 



CAPE DISAPPOINTMENT 



NEHALEM BEACH 



CAPE LOOKOUT 



WECOMA BEACH 



YAOUINA HEAD 



SIUSLAW RIVER 



COOS BAY 



FOUR MILE CREEK 



;ape ARAGO 



CAPE BLANCO 

 1 I I M I I I I I I I 1 



125° 124° 



Figure 1 



Location of purse seine tran-sect lines off Oregon and Washingtt)n. 



Size at ocean entrance of cutthroat and steelhead 

 trout caught during their first ocean summer was back- 

 calculated using the method of Lee as described in 

 Cariander (1981): 



Li = a -h ((Lc - a)/Sc)-Si, 



where Li = FL (mm) at time of ocean entry 



Lc = FL (mm) when captured 



Sc = total scale radius (mm at 88 x ) 



Si = scale radius at time of ocean entry 



