Enjeux et conséquences génomiques et écologiques des ensemencements de soutien du touladi (Salvelinus namaycush)

Authors: Morissette, Olivier
Advisor: Bernatchez, LouisSirois, Pascal
Abstract: Understanding and predicting management consequences on exploited fish stocks represents one of the major challenges of conservation science. There are still considerable uncertainties about the impacts of supplementation stockings on wild populations. Although generally efficient, supplementation can represent a major disturbance for populations, threatening to hinder their productivity and sustainability. Lake Trout (Salvelinus namaycush) is a North American freshwater salmonid whose exploitation by angling is strongly supported by stocking. The main objective of this thesis was to identify the ecological and genomic impacts of supplementation stockings on Lake Trout. To do this, we explored the impacts in three major domains of lake trout ecology; (1) growth and condition (2) trophic niche and (3) use of thermal habitats. These approaches allowed us to identify ecotypes (planktivorous or piscivorous) of the stocking source and target populations as a factor determining magnitude of short- and medium-term consequences. Specifically, our analyzes showed emergence of two divergent growth regimes in stocked planktivorous populations, with around 20 % of stocked individuals showing larger body size despite unsuitable habitat. The proportion of exogenous alleles of hybrid individuals correlated with a lower condition index, suggesting outbreeding depression. The analysis of stable isotope ratios of carbon (δ 13C) and nitrogen (δ15N) suggest a partition of niche for planktivorous stocked populations. Local individuals were displaced, probably by competitive exclusion, to a profundal/pelagic niche, atypical for these populations. Finally, biogenic carbonate thermometry, by analysis of otolith oxygen stable isotope ratios (δ18O), showed differential use of thermal habitats within stocked planktivorous populations. Stocked Lake Trout were using warmer habitats than hybrids and local individuals. These results underscored the importance of the inherent particularities of wild populations in the planning of management measures. Ignorance of these specific traits, and local adaptations, puts supplemented population at risk of declining productivity and survival.
Document Type: Thèse de doctorat
Issue Date: 2019
Open Access Date: 7 May 2019
Permalink: http://hdl.handle.net/20.500.11794/34743
Grantor: Université Laval
Collection:Thèses et mémoires

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