La Have River
3. DISCUSSION GÉNÉRALE
La caractéristique la plus importante des populations de Saumon atlantique en regard du concept de souche de salmonidés est que les stocks sont génétiquement uniques et que, par conséquent, ils ne peuvent pas être facilement remplacés. Il ne faut donc pas oublier, lorsque nous effectuons des manipulations de stocks de Saumon atlantique, dans le but d'augmenter non seulement le nombre mais aussi la qualité des saumons dans une rivière, que l'environnement d'une rivière d'ensemencement peut modifier le phénotype (les caractéristiques visibles) dans les limites de l'influence du contrôle génétique. Ceci a été clairement démontré dans le cas des stocks des rivières Saint-Jean et Western Arm Brook dont les âges et les tailles à la maturité sexuelle en conditions d'élevage variaient de ceux en conditions naturelles. Par ailleurs le projet de restauration de la rivière Margaree est encourageant; dans ce projet, une transplantation de stocks de saumons qui remontent tôt, issus du ruisseau Rocky (bassin de la rivière Miramichi) a produit de grandes quantités de poissons qui remontent tôt.
Par ailleurs, dans les cas de transferts, il ne faut pas forcer les stocks à subir des changements radicaux dans leur physiologie et leur comportement. Par exemple, si une rivière ne possède qu'un stock de saumons qui remontent tardivement, il y a probablement une raison écologique qui explique un tel type de remontée, à savoir de faibles niveaux d'eau et des températures estivales élevées. Le transfert d'un stock de saumons à montaison hâtive dans ce type de rivière pourrait provoquer des retours saisonniers précoces pour une certaine période, mais ne pourrait proba-blement pas permettre le maintien à long terme d'une remontée de contingents hâtifs. Par conséquent, il est peu probable que nous puissions améliorer ce que nous offre la nature par le biais de la sélection naturelle.
Ce que nous offre la nature, c'est un grand nombre de stocks de Saumon atlantique dont chacun d'eux est adapté à un ensemble de conditions environnementales particulières. En conséquence, tout transfert de stocks ne devrait être tenté qu'après avoir comparé rigoureusement les conditions environnementales et les caractéristiques biologiques des populations des rivières d'origine et d'ensemencement et après s'être assuré que ces conditions concordent. Le maintien de la qualité génétique sera essentielle pour la productivité à long terme. Les gestionnaires de la ressource Saumon atlantique devraient se préoccuper en tout premier lieu de la préservation des stocks existants. Le meilleur moyen d'y parvenir est de s'assurer d'un nombre convenable de reproducteurs et de procéder au maintien ou à l'amélioration des conditions environnementales naturelles de production.
REMERCIEMENTS
Je remercie Messieurs James Martin et John Bailey pour leurs suggestions pertinentes lors de la rédaction du manuscrit. Les tableaux ont été dressés par MM. Bill McMullon et Frank Cunningham. Mesdames Jeanine Hurley et Brenda Best ont dactylographié le manuscrit.
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INDICATEURS DE LA PRODUCTIVITE
DES RIVIÈRES QUÉBÉCOISES
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