Abstract
Long-distance migrations can be energetically demanding and can represent phases of high mortality. Understanding relationships between body condition and migratory performance can help illuminate the challenges and vulnerabilities of migratory species. Juvenile anadromous sockeye salmon (Oncorhynchus nerka) may migrate over 1000km from their freshwater nursery habitats to estuary and ocean feeding grounds. During the period corresponding to the seaward migration of sockeye salmon, we held smolts in the laboratory to ask the following: (i) Does non-feeding migration duration influence prolonged swim performance and survival? (ii) What are the relationships between individual body condition and swim performance and survival? Wild sockeye salmon were intercepted during their migration and held without food for up to 61days to represent the non-feeding freshwater migration and the extremes of poor estuary habitat. We conducted 40 sets of prolonged swim trials on 319 fish from 3 treatment groups that represented entrance to the marine environment on (i) an average,(ii) a delayed and (iii) a severely delayed migration schedule. Experimentally controlled freshwater migration duration did not impact swim performance or survival. Swim performance decreased concomitant with condition factor, where smolts with a Fulton's condition factor of <0.69 were less likely (<50% probability) to complete the swim test (90min swim test, at ~0.50m/s). Survival of salmon smolts in the laboratory was less likely at energy densities of less than 3.47MJ/kg. Swim performance decreased much sooner than survival, suggesting that swim performance, and therefore condition factor, may be a good indicator of survival of migratory smolts, as fish with reduced swim performance will likely be predated. These two relationships, one more ecologically relevant and one more clinical, help reveal the limits of long-distance migration for juvenile salmon and can be used to determine population-specific starvation risk associated with various freshwater and marine habitat conditions.
Highlights
Long-distance migrations are often challenging life history phases with higher mortality rates compared to stationary phases (Sillett and Holmes, 2002; Alerstam et al, 2003; Klaassen et al, 2014; Lok et al, 2015; Clark et al, 2016)
During the period corresponding to the seaward migration of sockeye salmon, we held smolts in the laboratory to ask the following: (i) Does non-feeding migration duration influence prolonged swim performance and survival? (ii) What are the relationships between individual body condition and swim performance and survival? Wild sockeye salmon were intercepted during their migration and held without food for up to 61 days to represent the non-feeding freshwater migration and the extremes of poor estuary habitat
Wild sockeye salmon smolts kept for up to 61 days without food decreased in condition factor, energy density and lipid and protein content, and increased in water content throughout the period of food deprivation
Summary
Long-distance migrations are often challenging life history phases with higher mortality rates compared to stationary phases (Sillett and Holmes, 2002; Alerstam et al, 2003; Klaassen et al, 2014; Lok et al, 2015; Clark et al, 2016). Migratory success or failure may be controlled by variation in individual condition and energetics within and across populations. Red knots (Calidris canutus rufa) with higher body condition (size-corrected mass) had faster migration to breeding grounds, higher migration success (survival), and were more likely to have bred successfully, than those of lower body condition (Duijns et al, 2017). Lower quality individuals are more likely to be predated during migration (Dierschke, 2003; Tucker et al, 2016). Body condition at the beginning of the migration can influence subsequent performance, thereby driving carryover effects across life stages and habitats. Understanding the relationship between body condition and the survival of migrating animals could help clarify their limits and vulnerabilities to environmental or anthropogenic disturbances in habitat or migratory conditions
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