Mature male parr contribution to the effective size of an anadromous Atlantic salmon (Salmo salar) population over 30 years

Abstract

We 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 threatened (COSEWIC 2010). We 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. We estimated the annual effective number of breeders (Nb) and the generational effective population size (Ne) through genetic methods and demographically using the adult sex ratio. Comparisons between genetic and demographic estimates show that the adult 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 adult males.

Effective number of breeders in relation to census size as management tools for Atlantic salmon conservation in a context of stocked populations

“…This corroborates previous studies in Atlantic salmon (e.g. Palstra et al 2009;Johnstone et al 2013;Perrier et al 2013). N b / N c temporal variation has also been reported in other salmonid species (Heath et al 2002;Palm et al 2003).…”

“…Palstra et al 2009, Johnstone et al 2013, Perrier et al 2014. Correcting these N b estimates following the method developed by Waples et al (2014) to take into account probable overlapping generations in Atlantic salmon from Quebec, N b(adj) values were reduced by *15 % compared to N b and ranged from 41 to 696 with an average of 211.…”

“…Several authors reviewed N e /N c estimates in many species from various taxa and reported variable values from 10 -6 to above 1, averaging 0.34 (Frankham 1995) and 0.19 (Palstra and Ruzzante 2008). However, for salmonids it is also important to consider that these estimates are calculated without considering mature male parr, which may substantially decrease N c estimates and thus upwardly biasing N e /N c estimates (Saura et al 2008;Johnstone et al 2013;Perrier et al 2014). …”

Simple life-history traits explain key effective population size ratios across diverse taxa

“…This argues for caution in interpreting results for individual species, but this source of random variation would only be rspb.royalsocietypublishing.org Proc R Soc B 280: 20131339 expected to add noise to our multispecies analyses. However, if cryptic population components are not accounted for in life tables [40], results could be misleading. Our model accounts for skewed adult sex ratios caused by differential survival of males and females, but we assumed equal sex ratio at birth.…”

Eco-Evolutionary Interactions as a Consequence of Selection on a Secondary Sexual Trait

“…Łukasik et al, 2006;Smallegange, 2011a,b;Tomkins et al, 2011), how a change in the environment (e.g. by selective harvesting) affects the interplay between ecological and evolutionary dynamics within ARP populations is still unclear ( Johnstone et al, 2013;Piou and Prévost, 2013;Smallegange and Johansson, 2014).…”