14 



Abstract.— Microsatellite DNA varia- 

 tion at six microsatellite loci (Omy77, 

 Ots3, OtslOO, OtslOS, Otsl07, and 

 OtslOS) was examined in approximately 

 900 sockeye salmon, Oncorhynchus nerka, 

 collected between 1987 and 1995 from 

 three stocks on the west coast of Van- 

 couver Island, British Columbia, Canada. 

 Variation in allele frequencies among 

 stocks was, on average, about 12 times 

 greater than temporal variation within 

 stocks. Individual locus Fgj estimates 

 ranged from 0.013 to 0. 107 among stocks, 

 with an overall value of 0.056. Analysis 

 of simulated mixed-stock samples indi- 

 cated that data from four to six of the 

 microsatellite loci surveyed would enable 

 relatively accurate and precise estimates 

 of stock composition for mixtures com- 

 posed offish from the three stocks. Appli- 

 cation of the mixture analysis to 1100 fish 

 sampled in Barkley Sound and Albemi 

 Inlet fisheries during 1997 indicated that 

 sockeye salmon from Great Central Lake 

 constituted about 70% of the commercial 

 catch. The later time of return of sock- 

 eye salmon from Henderson Lake than 

 of those from Great Central or Sproat 

 Lake as previously indicated by analysis 

 of parasite frequencies was confirmed in 

 the 1997 fishery sampling. Stock com- 

 position of catches varied among gears, 

 presumably owing to gear selectivity. 



Microsatellite DNA variation and estimation 

 of stock composition of sockeye salmon, 

 Oncorhynchus nerka, in Barkley Sound, 

 British Columbia - 



Terry D. Beacham 



Khai D. Le 



Monique R. Raap 



Kim Hyatt 



Wilf Luedke 



Ruth E. Withler 



Pacific Biological Station 



Department of Fishenes and Oceans 



Nanaimo, British Columbia 



Canada V9R 5K6 



E-mail address (for TD Beacfiam) beachamtig pac.dfo-mpo gc ca 



Manuscript accepted 27 April 1999. 

 Fish. Bull. 98:14-24(20001. 



In the sockeye salmon (Oncorhyn- 

 chus nerka ) fishery in Barkley Sound 

 on the west coast of Vancouver 

 Island, three stocks (Sproat Lake, 

 Great Central Lake, and Henderson 

 Lake) account for all of the catch in 

 the mixed-stock fishery (Hyatt and 

 Steer, 1987) (Fig. 1). These stocks 

 have been exploited for over 100 

 years, but the area of the fishery 

 has changed. The present fishery is 

 conducted over a wide area in Bar- 

 kley Sound. Lake fertilization has 

 been used to increase production of 

 Barkley Sound sockeye salmon ( LeB- 

 rasseur et al., 1978; Hyatt and Stock- 

 ner, 1985). Of the lakes sampled 

 in our study, Great Central Lake 

 has been fertilized most extensively, 

 with annual applications of fertilizer 

 between 1970 and 1973, and from 

 1977 to the present. Sproat Lake was 

 fertilized between 1985 and 1987, 

 and Henderson Lake has been fertil- 

 ized from 1976 to the present. 



Assessment of the effects of ferti- 

 lization on the productivity of Great 

 Central and Henderson lakes re- 

 quired accurate and reasonably pre- 

 cise estimates of stock composition in 

 the Barkley Sound sockeye salmon 

 catch. The frequency of occurrence 

 of two myxosporean parasites, Myxo- 



bolus arcticus in the brain and Hen- 

 neguya salmonicola in the muscle, 

 differed substantially among sock- 

 eye salmon in the three lakes during 

 1977-84 (Quinn et al., 1987), and 

 these differences in prevalence were 

 used to provide estimates of stock 

 composition in the fishery until 1984 

 (Steer et al., 1986, 1988). Sockeye 

 salmon from Sproat Lake and Great 

 Central Lake accounted for 95% of 

 the catch from 1980 to 1984 (Hyatt 

 and Steer, 1987). In the 1990s, it 

 became apparent that the frequency 

 of occurrence of the two parasites had 

 changed in Great Central Lake sock- 

 eye salmon (Beacham et al., 1998), 

 and fishery managers no longer con- 

 sidered estimates of stock compo- 

 sition derived from parasites to be 

 reliable for management decisions. 

 The timing of the change in para- 

 site frequency of occurrence between 

 1984 and the 1990s was unknown, 

 rendering post-1984 estimates of 

 stock composition and associated 

 estimates of individual lake produc- 

 tivity uncertain. It became impera- 

 tive to develop a reliable alternative 

 method of stock identification that 

 could be applied to fishery samples 

 for accurate estimation of both catch 

 and productivity by stock. 



