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Parental contributions to the early life history traits of juvenile sockeye salmon (Oncorhynchus nerka) : the roles of spawner identity and migratory experience Nadeau, Patrick Sylvain

Abstract

Pacific salmon (Oncorhynchus spp.) undergo arduous upstream migrations In order to spawn. To date, much scientific attention has focused on why certain migrants succeed in reaching their destination while others die trying. Less is known about how 'successful' spawners differ in the quality of the progeny they produce. Using sockeye salmon O. nerka (Walbaum) as a model, two artificial fertilization experiments were conducted to investigate the relationships between individual salmon and their offspring. In the first experiment, I evaluated survival, size, and burst swimming ability in fry of known parentage (spawners from the Weaver Creek population). After four months of exogenous feeding, fry size remained under significant maternal influence. Paternal identity did not affect size but significantly influenced both egg and fry survival. Burst swimming ability was not affected by parentage and only weakly associated with offspring size. In the second experiment, I evaluated an 'energetic trade-off' hypothesis which proposes that because adults migrate with a fixed energy budget while completing sexual maturation, investments to reproductive development may be impaired by an increase in the costs of swimming to reach spawning grounds. This hypothesis was evaluated by subjecting migrants to two different 'migration difficulties' (i.e. current speeds). Fish in the 'fast' treatment expended more energy than those in the 'slow' and also showed signs of greater physiological stress. However, these differences did not appear to influence allocations to reproductive development in terms of sex trait morphology, ovulation timing, and reproductive hormone levels. Likewise, the survival, incubation time, and size of progeny were not related to the treatments experienced by their parents. These traits were nonetheless influenced by parental identity, with significant contributions from both male and female parents. Regression models showed that offspring size and survival were linked to certain aspects of maternal condition at the time of fertilization, including size, stress, and energy levels.

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