Data from: Estimating the effective number of breeders from single parr samples for conservation monitoring of wild populations of Atlantic salmon Salmo salar

This study assesses whether the effective number of breeders (Nb) can be
estimated using a time and cost-effective protocol using genetic sibship
reconstruction from a single sample of young-of-the-year (YOY) for the
purposes of Atlantic salmon Salmo salar population monitoring. Nb was
estimated for 10 consecutive reproductive seasons for S. salar in the
River Nivelle, a small population located at the rear-edge of the species
distribution area in France, chronically under its conservation limit and
subjected to anthropogenic and environmental changes. Subsampling of real
and simulated data showed that accurate estimates of Nb can be obtained
from YOY genotypes, collected at moderate random sampling intensity,
achievable using routine juvenile electrofishing protocols. Spatial bias
and time elapsed since spawning were found to affect estimates, which must
be accounted for in sampling designs. Nb estimated in autumn for S. salar
in the River Nivelle was low and variable across years from 23 (95% C.I.
14–41) to 75 (53–101) and was not statistically correlated with the
estimated number of returning adults, but it was positively correlated
with the estimated number of YOY at age 9 months. Nb was found to be lower
for intermediate levels of redd aggregation, suggesting that the strength
of the competition between males to access females affects reproductive
success variance depending on redd spatial configuration. Thus,
environmental factors such as habitat availability and quality for
spawning and YOY development predominate over demographic ones (number of
returning adults) in driving long-term population viability for S. salar
in the River Nivelle. This study showcases Nb as an integrated parameter,
encompassing demographic and ecological information about a reproductive
event, relevant to the assessment of both short-term effects of management
practices and long-term population conservation status.