Sammendrag
1. Climate change poses a challenge to wild fishes, yet little is known about the
behavioural use and metabolic consequences of thermally heterogeneous water
encountered by wild salmon during their energetically demanding upstream
spawning migration.
2. Temperature, body size and activity levels were modelled to predict energy
depletion of salmon during their spawning migration in rivers. Archival temperature
loggers revealed the thermal habitat of adult migrating Atlantic salmon
(Salmo salar Salmonidae), which we used to apply bioenergetics models that estimated
size-dependent temperature-driven metabolic expenditures as part of the
costs of the migration.
3. Between July 16 and August 19, the mean water temperature experienced by
salmon (tFISH) ranged from 11.5 to 18.0°C (14.5 ± 1.2 SD °C) and closely followed
the ambient surface water temperature (tRIVER) of the river (11.5–18.5°C;
14.8 ± 1.4°C) such that the regression equation tFISH = 3.24 + 0.76 (tRIVER) was
highly correlated with observations (R2 = 0.94).
4. Although temperature increases were predicted and confirmed to increase energetic
costs, rates of energy depletion were more sensitive to changes in swimming
speed and body size than to temperature increases in the range explored
for this system.
5. We conclude that warming could contribute to changing life history phenotypes
of salmon in some rivers, for example, delayed river entry or reduced probability
of iteroparity, with potentially more dire consequences for smaller individuals.
bioenergetics, fisheries, iButton, iteroparity, telemetry
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