Orsi and Jaenicke. Marine distribution and origin of prerecruit Oncorhynchus tshawytscha 



493 



Alaska ocean-type chinook salmon of age 0.1 begin 

 to arrive in the marine waters of southern region of 

 southeastern Alaska in February and May, and by 

 September, non-Alaska chinook salmon age 0.1, as 

 well as those 0.2 and 0.3, are distributed throughout 

 the marine waters of southeastern Alaska. 



The temporal and spatial distribution of stream- 

 type chinook salmon in southeastern Alaska appears 

 more complex than that of ocean-type stocks. We 

 found that age 1.0 chinook salmon in September 

 originated from southeastern Alaska, British Colum- 

 bia, Washington, and Oregon. Age 1.0 stocks from 

 southeastern Alaska were almost exclusively found 

 in inside waters of the southern and central 

 regions; Orsi et al. ( 1987) also identified age 1.0 

 fish from these stocks in the northern region. 

 Age 1.0 stocks from British Columbia were 

 found exclusively in inside waters of the south- 

 ern region. Age 1.0 chinook salmon from Wash- 

 ington and Oregon stocks were recovered in 

 both inside and outside waters of the southern 

 region and in outside waters of the central re- 

 gion. These recoveries corroborate the external 

 tagging studies of Hartt and Dell ( 1986). Healey 

 (1983, 1991) reported that the residence of 

 stream-type chinook salmon in estuaries and 

 sheltered coastal waters is generally brief and 

 that fish move offshore during their first sum- 

 mer at sea, in contrast to ocean-type fish, which 

 remain in sheltered coastal waters. Our data 

 support his hypothesis with respect to stream- 

 type chinook salmon from Washington and Or- 

 egon. However, our recoveries of Alaska and 

 British Columbia stream-type chinook salmon 

 in inside waters during September, and during 

 the ensuing year in February and May, suggest 

 a more protracted residence or limited marine 

 migration for portions of stocks from these 

 regions. 



The limited marine migration of some Alaska 

 stream-type stocks of chinook salmon could have a 

 genetic basis. Although Alaska stocks of chinook 

 salmon are almost exclusively stream-type, electro- 

 phoretic evidence suggests that southeastern Alaska 

 stocks are genetically intermediate between stream- 

 type stocks of western Alaska and ocean- and stream- 

 type stocks of the Pacific Northwest (Gharrett et al., 

 1987). Therefore, following the Wisconsinan glacial 

 age, some southeastern Alaska drainages were prob- 

 ably colonized by ocean-type stocks. These fish may 

 have selected a stream-type freshwater life history trait 

 as a result of low "growth opportunity" in northern lati- 



30 

 1 5 



3 



CL 



Inslde waters 



n = 2.090 (456) 



O O Ala ska 



Q Q British Columbia 



• 1 



1< 



Sep 



10) 



Fab 



(") 



May 



(34) 

 Sep 



(2) 



!.■!■ 



25! 

 May 



(2) 

 Sep 



Age - 



Age- 1 



Age - 2 



Figure 5 



Catch rate of chinook salmon, Oncorhynchus tshawytscha, by 

 ocean age and season in inside and outside marine waters of 

 southeastern Alaska, 1986-87. Catch rate is based on the ex- 

 panded numbers of coded- wire-tagged fish caught per hour. Ac- 

 tual numbers of coded-wire— tagged fish are shown in parentheses. 



