GENETIC STOCK IDENTIFICATION OF ATLANTIC SALMON USING SINGLE-LOCUS MINISATELLITE DNA PROFILES

The successful application of genetic stock identification (GSI) in mi xed fisheries for Pacific salmon species has demonstrated dearly the p otential of the approach as an aid to effective management of salmonid populations. Low levels of genetic variability detectable by protein electrophoresis have limited its utilization in Atlantic salmon Salmo salar, management. However, recent developments in the detection of hi ghly variable minisatellite loci, mean that the GSI technique is now a pplicable in this species. An extensive baseline survey of the River S hannon system in Ireland, involving a total of 1252 juvenile Atlantic salmon collected from nine tributaries. screened for three highly vari able minisatellite DNA loci (Ssa-A45/1, Ssa-A45/2/1 and Str-A9), prese nted a suitable database to assess this type of mixed fisheries approa ch. Allozyme analysis, carried out on the same fish, allowed the perfo rmance of GSI on minisatellite DNA data to be compared directly with c onventional data using simulations. Initial tests involved the creatio n of 'mixture samples' of specified compositions from the database, to determine the bias involved and the degree of precision achievable in the estimation of the composition of the mixture sample. Iterations o f this procedure. simulated resampling of a mixture stock, thus enable d bias and precision to be estimated. The effect of size of the mixtur e sample was also assess,pd in this way. It was then possible to exami ne the compositions of actual mixture samples (using minisatellite DNA analysis only), which consisted of 200 unmarked grilse (one sea-winte r) and 50 unmarked multi-sea-winter salmon, collected as they passed u pstream through traps located near the base of the system. Sampling in this case involved the non-destructive collection of adipose fin core s (an important consideration as valuable broodstock were involved). T he initial analysis revealed that allozymes require much larger sample sizes than minisatellites to achieve comparable accuracy and precisio n. It also appeared that GSI analysis, based on just three minisatelli te loci, can provide very useful estimates of stock composition, even from a mixture sample comprising of stocks from within a single river system. (C) 1995 The Fisheries Society of the British Isles