LONG-TERM EVIDENCE THAT PRECOCIOUS PARR CAN SIGNIFICANTLY INCREASE THE EFFECTIVE SIZE OF A POPULATION OF ATLANTIC SALMON (SALMO SALAR)

Abstract

I describe temporal changes in the genetic composition of a small anadromous Atlantic salmon (Salmo salar) population from South Newfoundland, an area where salmon populations are considered as Threatened (COSEWIC 2010). I examined the genetic variability (13 microsatellite loci) in 869 out-migrating smolt and post-spawning kelt samples, collected from 1985 to 2011 for a total of 22 annual collections and a 30 year span of assigned cohorts. I estimated the annual effective number of breeders (Nb) and the generational effective population size (Ne) through genetic methods and demographically using the anadromous sex ratio. Comparisons between genetic and demographic estimates show that the anadromous spawners inadequately explain the observed Ne estimates, suggesting that mature male parr are significantly increasing Nb and Ne over the study period. Spawning as parr appears to be a viable and important strategy in the near absence of anadromous males.