PEARCY and FISHER: MIGRATIONS OF COHO SALMON 



salmon during their first summer in the ocean. 

 Based on recoveries of maturing coho salmon that 

 were tagged a year earlier at sea during April- 

 October 1956-70, Hartt and Dell (1986) con- 

 cluded that juvenile coho salmon from the Colum- 

 bia River, Oregon, and California may form a 

 large proportion of the coho stocks that migrate 

 north along the coast each summer. Of the 70 

 recoveries of tagged fish that were released be- 

 tween Kodiak Island and 56°N, 37% were recov- 

 ered the following year in the area of the Colum- 

 bia River and Oregon-California; of the 59 

 recoveries offish released between 56°N and Cape 

 Flattery, 47% were recovered in these southern 

 regions. In all, 25% of the recoveries were from 

 Oregon-California, 16% from the Columbia 

 River, 14% from Washington, 33% from British 

 Columbia, and 12% from Alaska. 



Loeffel and Forster (1970) concluded that pat- 

 terns of radioactive ^^Zn in juvenile coho salmon 

 collected in the northeastern Pacific supported 

 the concept of a northerly migration from Oregon 

 and Washington into the Gulf of Alaska during 

 the summer. They found that juvenile coho 

 salmon captured off the west coast of Vancouver 

 Island in June and July 1967 contained ^^Zn, pre- 

 sumably originating from neutron activation of 

 Columbia River water used to cool the nuclear 

 reactors at Hanford, WA. ^^Zn levels decreased 

 in fish caught farther to the north (54°42'N- 

 58°24'N) in July-September of 1967. The authors 

 thought the low concentrations in northern sam- 

 ples represented background levels and that fish 

 with relatively high levels of ^^Zn had associated 

 with the Columbia River plume and subsequently 

 migrated north from the Oregon- Washington re- 

 gion. They found low ^^Zn levels in 1968, how- 

 ever, and no pronounced latitudinal gradients. 

 Furthermore, they reported none of the many fin- 

 marked juvenile coho salmon released from Ore- 

 gon and Washington hatcheries in 1967 and 1968 

 north of Juan de Fuca Strait. Hence their evi- 

 dence for northward movements of Columbia 

 River or Oregon-Washington coho salmon was 

 equivocal. 



During June and July 1984, research was con- 

 ducted with the NMFS Auke Bay Laboratory in 

 waters from northern California to southwest 

 Alaska from the FV Pacific Warwind and Bering 

 Sea , both making round hauls with the same size 

 of purse seine, to sample juvenile coho in waters 

 north of Oregon and Washington: 37 sets were 

 made in coastal waters of British Columbia, and 

 39 were made in coastal waters and 29 in inland 



waters (bays, inlets, and ^ords) of southeastern 

 Alaska. Of the 371 juvenile coho salmon captured 

 in these regions, 77% were caught in inland 

 waters of southeastern Alaska. The seven CWT 

 juvenile coho salmon captured were all from 

 Alaska inland waters and all originated from 

 Alaska hatcheries (Auke Bay Laboratory 1984a). 

 A later cruise in southeast Alaska by the Auke 

 Bay Laboratory in August 1984 caught eight 

 CWT coho salmon, also all from inland waters 

 and from Alaskan hatcheries (Auke Bay Labora- 

 tory 1984b). 



Of the 14 CWT juvenile coho salmon collected 

 in other purse seines, gill nets, and special troll 

 gear in waters of southeastern Alaska during 

 1982, 1983, and 1985, 12 originated from Alaska 

 hatcheries and 2 originated from Washington 

 hatcheries (Auke Bay Laboratory 1983; Jaenicke 

 et al. 1984; Orsi et al. 1987). Table 6 shows that 

 only 5 of 25 CWT juvenile coho salmon caught in 

 Alaskan waters during 1977-83 were from hatch- 

 eries south of Alaska, indicating that most juve- 

 nile coho salmon caught in southeastern Alaska 

 during the summer originated from Alaska and 

 not from southern regions. 



Hartt (1980) and Hartt and Dell (1986) recog- 

 nized that their data did not indicate the propor- 

 tion of southern stocks that made northerly mi- 

 grations, but they concluded that a large 

 proportion is probable, since juvenile coho salmon 

 were consistently caught in most seine sets 

 throughout the area sampled. They estimated 

 that the average density of juvenile salmonids in 

 coastal waters between 56°N and 60°N off south- 

 eastern Alaska during August and September 

 1964-68 was 1,500 km"^. The average density of 

 juvenile coho salmon in this area during these 

 two months was only 82 km~^ (Hartt and Dell 

 1986, app. A). During August and September 

 1981-84, the average density of juvenile coho 

 salmon in our round hauls between Cape Flat- 

 tery, WA and Cape Arago, OR to 37 km offshore 

 was 350 km"^, several times the estimates of 

 Hartt and Dell for the same months of the year. 

 This suggests that juvenile coho salmon may be 

 found in higher densities off Oregon and Wash- 

 ington than southeastern Alaska during late 

 summer, assuming that distributions and abun- 

 dances in the late 1960s and early 1980s were 

 similar. This trend for higher abundances of juve- 

 nile coho salmon off Oregon and Washington than 

 in coastal waters farther north was also found 

 during July 1984 (Table 7), although average 

 catches off Washington and Oregon were not as 



191 



