640 



Abstract — Little is known about the 

 ocean distributions of wild juvenile 

 coho salmon off the Oregon- Washington 

 coast. In this study we report tag recov- 

 eries and genetic mixed-stock estimates 

 of juvenile fish caught in coastal waters 

 near the Columbia River plume. To sup- 

 port the genetic estimates, we report 

 an allozyme-frequency baseline for 89 

 wild and hatchery-reared coho salmon 

 spawning populations, extending from 

 northern California to southern Brit- 

 ish Columbia. The products of 59 allo- 

 zyme-encoding loci were examined with 

 starch-gel electrophoresis. Of these, 56 

 loci were polymorphic, and 29 loci had 

 ^0 9.5 levels of polymorphism. Average 

 heterozygosities within populations 

 ranged from 0.021 to 0.046 and aver- 

 aged 0.033. Multidimensional scaling of 

 chord genetic distances between sam- 

 ples resolved nine regional groups that 

 were sufficiently distinct for genetic 

 mixed-stock analysis. About 2.9% of the 

 total gene diversity was due to differ- 

 ences among populations within these 

 regions, and 2.6% was due to differences 

 among the nine regions. This allele-fre- 

 quency data base was used to estimate 

 the stock proportions of 730 juvenile 

 coho salmon in offshore samples col- 

 lected from central Oregon to northern 

 Washington in June and September- 

 October 1998-2000. Genetic mixed- 

 stock analysis, together with recoveries 

 of tagged or fin-clipped fish, indicates 

 that about one half of the juveniles 

 came from Columbia River hatcheries. 

 Only 22% of the ocean-caught juveniles 

 were wild fish, originating largely from 

 coastal Oregon and Washington rivers 

 (about 20%). Unlike previous studies 

 of tagged juveniles, both tag recoveries 

 and genetic estimates indicate the pres- 

 ence offish from British Columbia and 

 Puget Sound in southern waters. The 

 most salient feature of genetic mixed 

 stock estimates was the paucity of wild 

 juveniles from natural populations in 

 the Columbia River Basin. This result 

 reflects the large decrease in the abun- 

 dances of these populations in the last 

 few decades. 



Genetic analysis of juvenile coho salmon 

 iOncorhynchus kisutch) off Oregon and 

 Washington reveals few Columbia River wild fish' 



David J. Teel 



Donald tA. Van Doornik 



David R. Kuligowsl<i 



Conservation Biology Division 



Northwest Fishenes Science Center 



2725 Montlal<e Boulevard East 



Seattle, Washington 98112-2097 



Present address (for D. J. Teel): Manchester Research Laboratory 



7305 Beach Drive E. 



Port Orchard, Washington 98366 

 Email address (for D J Teel) David Teel@NOAA.gov 



W. Stewart Grant 



PC Box 240104 



Anchorage, Alaska 99524-0104 



Manuscript approved for publication 

 15 January 2003 by Scientific Editor 



Manuscript received 4 April 2003 at 

 NMFS Scientific Publications Office. 



Fish. Bull. 10 1:640-652 (2003). 



Nearshore and riverine distributions 

 of maturing Pacific salmon (Oncorhyn- 

 chus spp.) are well known, largely 

 because of the prevalence of salmon 

 fisheries and the tremendous amount 

 of information gathered to manage 

 these fisheries. Out-migration timings 

 and abundances of smolts in streams 

 as they migrate to the sea are also well 

 known, but information on the distribu- 

 tions and stock origins of wild juveniles 

 in marine waters has been limited by 

 two factors. The first is that a large 

 amount of effort is needed to sample 

 marine-phase juveniles, which gener- 

 ally occur at low densities (Godfrey, 

 1965; Hartt and Dell, 1986; Orsi et al., 

 2000). The second factor is that stock 

 origins have been determined only for 

 coded-wire-tagged (CWT) hatchery 

 fish (e.g. Pearcy and Fisher, 1988; Orsi 

 et al., 2000). Because only small propor- 

 tions of hatchery juveniles are tagged, 

 samples of ocean-caught salmon are 

 largely a mixture of hatchery and wild 

 fish of unknown stock origins. Genetic 

 mixed-stock analysis, although used 

 routinely to estimate the stock compo- 

 sitions of mature returning salmon ( e.g. 

 Milncr et al., 1985; Shaklee et al., 1999; 

 Beacham et al., 2001), has not been 

 fully exploited to estimate stock origins 

 of immature salmon (but see Guthrie et 

 al., 2000). The study we describe here is 



the first to use genetic data to estimate 

 the stock origins of ocean mixtures of 

 juvenile coho salmon (O. kisutch). 



One goal of our study was to cre- 

 ate a baseline of allelic frequencies in 

 spawning populations of coho salmon 

 throughout the Pacific Northwest and 

 California. These data were previously 

 used by the National Marine Fisheries 

 Service (NMFS) to define evolutionarily 

 significant units (ESUs) for evaluation 

 under the Endangered Species Act 

 (Johnson et al., 1991; Weitkamp et al., 

 1995). In the present study, we examine 

 levels of variability among populations 

 and use mixed-stock simulations to as- 

 sess the usefulness of such a data set 

 as a baseline for genetic mixed-stock 

 analysis. A second goal was to use this 

 baseline of population data to estimate 

 the stock compositions of juvenile coho 

 salmon collected in the early and late 

 summers of 1998, 1999, and 2000 off 

 the Oregon and Washington coasts by 

 the NMFS (Emmett and Brodeur 2000). 

 We use a standard approach to genetic 

 mixed-stock analysis that yields propor- 

 tional estimates of stock origin of fish 

 in a mixed-stock sample (e.g., Pella and 

 Milner, 1987). We compare early and 



* Contribution 388 to the U.S. GLOBEC pro- 

 gram. Woods Hole Oceanographic Institute, 

 Woods Hole, MA 02543. 



