Beacham: The use of DMA variation for stock identification of Oncorhynchus keta 



625 



The simulations suggest that relatively accurate 

 estimates of stock composition may be possible should 

 minisatellite DNA variation be applied to practical 

 fisheries management issues but that identification 

 of individual fish to specific regions, particularly in 

 North American stocks surveyed, is less accurate. For 

 example, estimated Fraser River stock composition 

 of pure samples of Fraser River chum salmon ranged 

 from 87 to 93% when resolved with an 18-stock 

 resampled southern British Columbia baseline, but 

 only about 31% of individual Fraser River fish were 

 correctly identified as of Fraser River origin when a 

 39-stock North Pacific baseline was used. About 26% 

 of the Fraser River individuals were classified as 

 originating from the east coast of Vancouver Island, 

 a result which may seem in conflict with the greater 

 separation observed between Fraser River and ECVI 

 stocks in the estimation of mixture composition. 

 However, estimation of stock composition of a mix- 

 ture and classification of individual fish in the mix- 

 ture are separate problems, with classification of 

 individual fish the more difficult problem. Data from 

 only a single fish that is to be identified are consid- 

 ered in classification problems, but data from all fish 

 in the mixture as a whole are considered when esti- 

 mates of stock composition are determined. Higher 

 levels of accuracy (99%) have been observed previ- 

 ously in estimation of chum salmon composition by 

 using the entire mixture sample rather than by clas- 

 sifying individual fish in the same mixture to region 

 of origin (<60%) (Fournier et al., 1984). 



Although analysis of minisatellite DNA variation 

 may be an effective method for estimation of stock 

 composition of chum salmon, a number of improve- 

 ments would be required before it could be applied 

 (either by itself or as an enhancement) to existing 

 stock identification techniques for chum salmon. 

 Determination of the allelic frequency distributions 

 or band counts at the minisatellite loci for all stocks 

 contributing significantly to fisheries, as well as 

 ensurance that sampling of the contributing popula- 

 tions is adequate to represent samples of the stock 

 that have been collected, would be required. 



Genetic variation provides a powerful means to 

 estimate stock composition of chum salmon catches. 

 The particular method used to screen variation will 

 depend on the issue to be resolved. Estimation of 

 stock composition to large regional groups could be 

 conducted with analysis of variation at protein-cod- 

 ing loci, in mitochondrial DNA, in minisatellite DNA, 

 or in the major histocompatability complex (MHO 

 genes (Miller and Withler, in press). Estimation of 

 local stock composition to a fine scale, such as to 

 tributaries of a major river system, will likely require 

 direct measurement of DNA variation. Surveys of 



variation at minisatellite loci provide one possibility 

 of achieving fine-scale estimation of stock composi- 

 tion, but analysis of variation at other minisatellite 

 loci, in addition to those utilized in the current manu- 

 script, will be required. No surveys of population 

 variation at microsatellite loci for chum salmon have 

 been conducted yet, although there may be great 

 potential in their application (e.g. Brooker et al., 

 1994). Given the relative ease of laboratory analysis 

 of variation at microsatellite loci, compared with that 

 at minisatellite loci, microsatellite loci may be more 

 practical than minisatellite loci, on a routine basis, 

 for stock-identification analysis. 



Acknowledgments 



Sampling of chum salmon stocks in British Colum- 

 bia was conducted by Clyde Murray and Wally 

 Barner of the Pacific Biological Station. Samples of 

 Japanese stocks were provided by M. Kaeriyama 

 (Fisheries Agency of Japan) and L. Park (National 

 Marine Fisheries Service), Russian stocks by N. 

 Varnavskaya (KOTINRO), and southeast Alaskan 

 stocks by J. Helle (National Marine Fisheries Ser- 

 vice). Laboratory analysis was conducted by J. 

 Khattra, L. Barton, and B. Ruston, and partially 

 supervised by E. Taylor. J. B. Taggart provided the 

 pSsa-A33 and pSsa-A34 probes. Funding for the re- 

 search was provided by the Department of Fisheries 

 and Oceans and by the Japan Science and Technol- 

 ogy Fund of the Department of Foreign Affairs. 



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