An integrated approach to studying the relationship between anadromy and iteroparity in Atlantic salmon (Salmo salar)

Bøe, Kristin (2019) An integrated approach to studying the relationship between anadromy and iteroparity in Atlantic salmon (Salmo salar). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Atlantic salmon is an anadromous species capable of spawning more than once during its lifecycle, being iteroparous. Increasing conservation concern has led to increased attention being paid to the potential short-term mitigating effects that iteroparous individuals may serve to populations suffering from low juvenile to adult recruitment. Despite the current research focus on repeat spawning Atlantic salmon, little is still known about how the iteroparous life cycle affects intrapopulation variation in marine movements and potential implications for population dynamics. The current thesis applied an integrated approach to studying the relationship between anadromy and iteroparity in Atlantic salmon from Newfoundland (Canada). Acoustic telemetry, scale pattern, stable isotope, fatty acid and mark-recapture analyses were included as analytical methods to investigate aspects of the relationship between iteroparity and anadromy and its importance in shaping the marine migratory patterns of Atlantic salmon. Using acoustic telemetry applied to 78 kelts and 90 smolts from two populations, I found that life stage influenced migratory movements and behaviour during the nearshore marine phase. Specifically, migratory movements were characterized by faster, more directed and less nocturnal movements by kelts as compared to smolts. These contrasts, however, varied by population, and the source of this variation was suggested to include responses to temporal and physical contrasts in the biotic and abiotic environment that shape the constraints imposed by trade-offs such as those between the need to reduce predation risk and increase growth and mass-gain. Using fatty acid (FA) and stable isotope analyses applied to 72 returning adults, I also found that life stage, as well as spawning history, influence migratory movements and dietary patterns during the at-sea phase. Specifically, significant differences in FA composition and ratios of δ¹⁵N in dorsal muscle tissue were identified, which supported the hypothesized divergent use of dietary sources among the different spawning history groups. Significant differences in FA composition, as well as lipid density, were also found among the different spawning histories in 69 post-spawned Atlantic salmon sampled as they emigrated from the river. Furthermore, patterns in lipid density were consistent with patterns in kelt return rates to consecutive repeat spawning. Consecutively spawned kelts and females had significantly higher lipid density than first-time spawned kelts and males, and consecutively spawned kelts and females experienced higher return rates compared to first-time spawned kelts and males. It was suggested that these spawning history related contrasts in energetic and nutritional state in post-spawned Atlantic salmon may be a carry-over effect of contrasts in the non-breeding area as affected by spawning-history dependent migration strategies, or alternatively, may represent an adaptive response to increased survival and recovery potential with age.

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