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Fishery Bulletin 92(1). 1994 



size. An early component of coho salmon juveniles 

 could have moved offshore in June, prior to our sam- 

 pling effort. More extensive sampling from late 

 spring through fall is required to define the timing 

 of migrations of coho salmon in the waters of South- 

 east Alaska. 



The sizes of juvenile salmon we captured support 

 the findings of Hartt and Dell (1986) that fish in 

 more northern locations have been at sea longer 

 than those in southern locations. Hartt and Dell 

 (1986) observed a general increase in mean length 

 of juvenile salmon from south to north in the out- 

 side waters from Washington to Southeast Alaska. 

 In the coastal waters off Oregon and Washington, 

 larger, presumably older, juvenile coho salmon were 

 found farther north (Pearcy and Fisher, 1988). As- 

 suming they were similar in size on entering the sea, 

 the smaller fish in the southerly locations are recent 

 arrivals from nearby production areas, whereas the 

 larger fish in the northerly locations have been at 

 sea longer and probably migrated from more south- 

 erly production areas (Hartt and Dell, 1986). Our 

 studies also reveal juvenile salmon in Southeast 

 Alaska were larger in the outside waters than in- 

 side waters and farther offshore in the outside wa- 

 ters than closer to shore. The progression of juve- 

 nile salmon migrations over a season may be size- 

 dependent (Healey, 1982, 1984), and certain phases 

 of migration may depend on fish reaching a thresh- 

 old size. According to Hartt and Dell ( 1986), the off- 

 shore migration into the Gulf of Alaska of juvenile 



Table 5 



Comparison of mean fork lengths (FL) of juvenile salmonids caught in 

 the marine waters (all habitats pooled) of Southeast Alaska and north- 

 ern British Columbia in 1983-84. Sample size = n; standard deviation 

 of the size in mm = s. The hypothesis was that there were no size dif- 

 ferences between species during the same period. The rejection crite- 

 ria were adjusted for multiple comparisons so that experimental error 

 did not exceed a = 0.05. Species having the same letter in a column were 

 not significantly different by size. 



August 1983 



July 1984 



Salmon 

 species 



mean FL 



Immi 



n 



mean FL 

 (mm) 



n 



Pink' 1,323 



Chum 2 299 



Sockeye'* 83 



Coho'' 188 



155 c 

 165 6 

 162'' 

 232° 



29 

 31 



23 



22 



444 

 108 

 347 



277 



130' 

 129 r 

 138'' 

 193 



1 1 

 17 

 20 



30 



1,461 

 289 

 234 

 241 



Oncorhynchus gorbuscha. 

 b O. keta. 

 c O. nerka. 

 d O. kisutch. 



pink, chum, and sockeye salmon does not begin until 

 September or October when fish are 180-230 mm 

 or greater in mean FL. However, our findings show 

 that these species are found offshore earlier (in 

 August) and at a much smaller size (145-170 mm 

 mean FL). 



Width of migration band 



Juvenile Pacific salmon typically migrate in 

 nearshore waters during their first few months at 

 sea (Straty, 1981); however, the width of this migra- 

 tion band varies regionally (Straty and Jaenicke, 

 1984; Hartt and Dell, 1986). Juvenile salmon con- 

 centrated within 37 km of shore along the broad 

 continental shelf (<183 m deep) off Oregon and 

 Washington (Miller et al., 1983; Pearcy and Fisher, 

 1990). Hartt and Dell (1986) concluded that the 

 band of juvenile salmon was within 37 km of shore 

 off Southeast Alaska where the continental shelf is 

 narrow, but that the band widened in the northern 

 Gulf of Alaska where the shelf is wider. 



Our results indicate that the coastal band of mi- 

 grating juveniles can be much wider than 37 km and 

 that the offshore migration beyond 37 km may be- 

 gin as early as August. Catches of juvenile salmon 

 74 km offshore — the maximum distance we fished 

 offshore — and the catch distributions indicate that 

 some juvenile salmon (pink, chum, and sockeye) may 

 have been abundant even farther seaward. Two- 

 thirds of the juvenile salmon captured in outside wa- 

 ters in August 1984 were beyond the continental shelf. 

 The width of the migration band is probably in- 

 fluenced by the Alaska Coastal 

 Current — a dominant feature 

 in the circulation of Gulf of 

 Alaska coastal waters. This 

 freshwater-driven current be- 

 gins along the British Colum- 

 bia coast and flows north then 

 west within 20 km of shore into 

 the Bering Sea (Royer, 1984). 

 The strength of this current is 

 affected by local precipitation, 

 wind, air temperature, and 

 other meteorological condi- 

 tions. Millions of juvenile 

 salmon migrate through the cur- 

 rent every year en route to 

 more oceanic waters. Cooney 

 (1984) theorized that the cur- 

 rent represents a critical early- 

 feeding habitat in the summer 

 and early fall. In modeling the 

 early-ocean limitations of Pa- 

 cific salmon production, Wal- 



August 1984 



mean FL 

 (mmi 



142'' 

 141 r 

 153'' 

 253° 



18 

 22 

 12 

 20 



