Main stem movement of Atlantic salmon parr in response to high river temperature

Abstract

Atlantic salmon become thermally stressed when water temperatures exceed 23°C. To alleviate this stress, they behaviourally thermoregulate by moving to patches of cold water, often forming large aggregations. These patches are known as thermal refuges. Given the consensus that climate change will increase temperatures in Atlantic salmon catchments, thermal refuges will become increasingly important in minimising summer mortalities. While the behaviour of salmonids within thermal refuges is fairly well understood, less is known about their main stem movement in search of thermal refuges or its thermal and temporal cues. We detail the results of a PIT telemetry study to investigate the main stem movement behaviour of thermally stressed Atlantic salmon parr in a temperature-impacted river. PIT antennas placed around two thermal refuges and at the upstream and downstream limits of their surrounding reach were used to record the movement of salmonids during a heatwave. We observed parr movement at the upstream and downstream antennas 135 min prior to the occurrence of the midpoint of aggregations in the thermal refuges, indicating that Atlantic salmon parr make reach-scale movements in search of cool water prior to aggregating. Logistic regression showed that the number of degree hours >28°C predicted the occurrence of main stem movement with a good degree of accuracy, indicating that this temperature represents a fundamental threshold causing Atlantic salmon parr to move towards cool water. Such data could be instrumental in allowing river managers to place limits on human activity within rivers, allowing salmon populations time to recover following heat stress events.

Riparian and geomorphic controls on thermal habitat dynamics of pools in a temperate headwater stream

“…The mature forest reach received the least direct solar radiation, showing the importance of the riparian habitat being composed of mature trees to act to maximize the shading factor (e.g., Newbold, Herbert, Sweeney, Kiry, & Alberts, ). This is also the only riparian habitat where groundwater resurgence was observed locally modifying the thermal regime of the stream by thermal stratification and creating potentially persistent thermal refugia as observed in other studies (e.g., Torgersen et al, ; Dugdale et al, ). Despite 35 years of riparian growth, pools in the restored forest reach (maximum 22.18°C, averaged daily variation = 3.06°C) exhibited greater daily variation in water temperature compared to pools within the mature forested reach.…”

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

“…The Ouelle River has a relatively stable population of Atlantic salmon (DFO, 2015). Like the LSWM, it is common for water temperatures within the Grande River and the Ouelle River to surpass thresholds of thermal stress for juvenile Atlantic salmon, with water temperatures >27-28°C occurring often in recent years Dugdale et al, 2016;Gendron, 2013). A ~2,400 m reach of the Grande River was selected as a study site and included two second-order cool tributaries (T1 and T2; daily T mean ± SE of T1 = 16.77 ± 1.56°C & T max = 18.91 ± 1.58°C; T2 T mean & T max = 17.00 ± 2.36°C & 17.34 ± 2.60°C throughout 2010 study period) located near the confluence with the Ouelle River ( Figure 1).…”

“…It was stipulated that these detections must occur throughout the warming period of the day (~7:00-17:00 hr) in the study rivers to eliminate fish detections observations that might not represent high temperaturedriven movements, that is diurnal movement (Gries, Whalen, Juanes, & Parrish, 1997;Thorpe, Morgan, Pretswell, & Higgins, 1988), or discharge-related refuge (Dugdale et al, 2016;Puffer et al, 2015). Using this method, an aggregation was classified as the detection of ≥2 unique PIT codes within a brief (≤1 hr) period of time.…”

Summer habitat and movements of juvenile salmonids in a coastal river of Washington State

“…In contrast to the observations in cold Alaskan streams, juvenile coho salmon have been observed to move horizontally and congregate into thermal refugia in rivers with warmer temperature regimes (Sutton & Soto, ). Similarly, juvenile Atlantic salmon ( S. salar ) in Canadian rivers migrate towards cool water patches, or thermal refugia, during warm summer months (Dugdale et al., ). Summer temperatures in the Chehalis River lie close to the upper extent of salmonid tolerance, similar to the studies that linked horizontal migrations and access to thermal refugia.…”

“…For example, pools provide important rearing areas for juvenile coho ( Oncorhynchus kisutch ) and Chinook salmon ( O. tshawytscha ) (Mossop & Bradford, ; Rosenfeld, Porter, & Parkinson, ), swifter flowing riffles with large substrate tend to be preferred by juvenile steelhead trout ( O. mykiss ) (Bisson, Sullivan, & Nielsen, ; Everest & Chapman, ), and large woody debris within pools provides cover from predators (Fausch & Northcote, ; Mossop & Bradford, ). Tributary junctions and other thermal refugia are important locations for juvenile salmon during low flows, especially in rivers with temperatures close to the upper threshold of thermal tolerances, and fish have been documented to seek thermal refugia through reach‐scale movements (Dugdale et al., ).…”