Comparing the behavioural thermoregulation response to heat stress by Atlantic salmon parr (Salmo salar) in two rivers

Abstract

Climate change is expected to increase the frequency and magnitude of extreme thermal events in rivers. The Little Southwest Miramichi River (LSWM) and the Ouelle River (OR) are two Atlantic salmon (Salmo salar) rivers located in eastern Canada, where in recent years, water temperatures have exceeded known thermal limits (~23°C). Once temperature surpasses this threshold, juvenile salmon exploit thermal heterogeneity to behaviourally thermoregulate, forming aggregations in coolwater refuges. This study aimed to determine whether the behavioural thermoregulation response is universal across rivers, arising from common thermal cues. We detailed the temperature and discharge patterns of two geographically distinct rivers from 2010 to 2012 and compared these with aggregation onset temperature. PIT telemetry and snorkelling were used to confirm the presence of aggregations. Mean daily maximum temperature in 2010 was significantly greater in the OR versus the LSWM (p = 0.005), but not in other years (p = 0.090–0.353). Aggregations occurred on 14 and 9 occasions in the OR and LSWM respectively. Temperature at onset of aggregation was significantly greater in the OR (Tonset = 28.3°C) than in the LSWM (Tonset = 27.3°C; p = 0.049). Logistic regression models varied by river and were able to predict the probability of aggregation based on the preceding number of hours >23°C (R2 = 0.61 & 0.65; P50 = 27.4°C & 28.9°C; in the OR and LSWM respectively). These results imply the preceding local thermal regime may influence behaviour and indicate a degree of phenotypic plasticity, illustrating a need for localised management strategies.

Characterizing physical habitat preferences and thermal refuge occupancy of brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar) at high river temperatures

“…Atlantic salmon parr were not limited fully to cold‐water refugia until ambient river temperature exceeded 27°C, an observation consistent with their higher temperature tolerance compared to brook trout. During five sampling days (non‐consecutive) when the ambient river temperature exceeded 25°C, small aggregations of salmon parr (3–6 fish) were observed on the fringe of, and within, cold‐water anomalies and all parr were within the cold‐water plume when the ambient river temperature reached 27°C, as also reported by Corey et al (). Corey, Linnansaari, Cunjak, and Currie () found repeated exposure to extreme temperature lowers the thermal threshold in salmon parr.…”

“…It is possible that salmon parr we observed were exposed to multiple temperature stress events and thus may have begun to aggregate at 25°C (Corey et al, ). Our observations and conclusions regarding temperature triggers of behaviours cannot unravel the effects of the thermal regime exposures the fish have experienced in‐year and over many years (Corey et al, ; Corey et al, ), but the observed salmon parr behaviour suggests that temperature sensitivities and response triggers are being affected in this northern, temperate river.…”

Ice cover exists: A quick method to delineate groundwater inputs in running waters for cold and temperate regions

“…However, smaller streams that are groundwater dominated can remain ice free to varying degrees (Figure ; Cunjak et al, ). In summer, river temperatures can exceed 30°C in the Miramichi (see Corey et al, ), whereas in winter, river temperatures are typically not observed to be much lower than 0°C (Cunjak & Caissie, ). Groundwater thermal regimes in the Miramichi vary with depth and display a lagging behaviour in relation to seasonal air temperature fluxes.…”

Effects of Topographic Resolution and Geologic Setting on Spatial Statistical River Temperature Models

“…Climate change is projected to have broad‐scale implications for river ecology including increasing pressure on native coldwater species (Corey et al, 2019; Wilbur et al, 2020) and highlights the importance of thermal refugia in the age of climate warming in northern temperate and boreal regions of the world. The models generated herein will prove useful in preliminary efforts by fisheries and land use management to (a) identify and (b) protect and conserve critical coldwater habitat in these northern temperate settings.…”

“…During high temperature events, salmonids will seek out thermal refugia, that is, colder water, to mitigate physiological stress (Corey et al, 2017; Wilbur et al, 2020). These refugia are most often groundwater features (Curry & Devito, 1996) and can vary from fine‐scale, localized bank seeps (Wilbur, 2012) and hyporheic upwellings (Krause et al, 2011), to broader‐scale, tributary inflows (Corey et al, 2019). At the southern extent of Atlantic Salmon and Brook Trout ranges, increasing river temperature associated with climate change is beginning to have negative effects on both species (Corey et al, 2019; Dugdale et al, 2016).…”