Challenging convention: the winter ecology of brown trout (Salmo trutta) in a productive and stable environment

Abstract

Summary Understanding of the winter ecology of stream salmonids is biased by research conducted in northern temperate and boreal regions dominated by hard rock geology. Such systems are driven by highly dynamic surface‐flow regimes and tend to be physically diverse, nutrient poor and influenced by ice. This study investigated how the behaviour of brown trout, Salmo trutta, inhabiting a stable groundwater‐fed, productive and comparatively warm southern English chalk stream differs from that described for other systems, and how this is translated to performance, measured as growth. Physical characteristics were mapped, and high‐resolution temperature data collected using a spatial array of data loggers installed throughout the study reach during the winter. A combination of passive integrated transponder and radio telemetry was used to monitor distribution, density, and movement of trout. Micro‐archival data storage tags inserted in some individuals provided information on temperature regimes experienced. Growth performance was calculated for recaptured fish. Trout density was positively related to depth and there was no evidence that temperature influenced microhabitat selection. Three patterns of movement were observed. Over three‐quarters of tracked fish exhibited high site fidelity and tended to remain in a single focal position throughout the study. Fourteen per cent of trout exploited more than one distinct location, while the remainder were detected at multiple locations and showed no preference for any one. Trout exhibited regular daily activity patterns and highly periodic local movements at dusk and dawn and tended to experience positive growth performance during periods that included winter. This study challenges the conventional view of salmonid winter ecology, which is biased towards populations that inhabit hard rock surface‐flow dominated rivers that experience the influence of ice. Despite inhabiting a distinctly different winter habitat template than more commonly studied populations, trout occupying a hydrologically stable and productive chalk stream exhibited behaviours similar to those described for elsewhere, yet performed considerably better.

Effects of Temperature and Spatial Scale on Rio Grande Cutthroat Trout Growth and Abundance

“…; Kemp et al. ). Additionally, strong hyporheic exchange not only influences stream temperature (White et al.…”

Estimating ecological flows for fish overwintering in plain rivers using a method based on water temperature and critical water depth

“…As the water temperature decreases, fish become less active and move to deeper, slower flowing water, or into near dense instream cover. Such behaviour has been documented for coho salmon (Swales, Lauzier, & Levings, ), brown trout (Kemp et al, ), Chinese carp, and Chinese bream (He & Deng, ). Due to the impact of water temperature on fish behaviour, the vertical distribution of water temperature may explain the fish overwintering habitat selection.…”

The importance of seasonal macrophyte cover for the behaviour and performance of brown trout (Salmo trutta) in a groundwater‐fed river

“…Performance, in terms of growth, is found to be largely positive in salmonids inhabiting groundwater‐fed rivers (French, Vondracek, Ferrington, Finlay, & Dieterman, ; Kemp et al., ). The lack of extremes in the abiotic environment (French et al., ) and high aquatic invertebrate abundance throughout the winter (Bouchard & Ferrington, ; Wright, ) probably mediates this.…”

“…A small sample were also implanted with micro archival data storage (DS) tags, data for which were used by Kemp et al. (). Prior to surgery, the functionality and frequency (between 173.199 and 173.994 MHz) of radio tags was verified using a hand‐operated receiver.…”

“…interstices of large substrates; Heggenes et al., ). High site fidelity might be expected as benefits of patch switching are low when growth remains positive (Kemp et al., ) and food availability is high (Wright, ), while periodic movements at dawn and dusk suggest that nocturnal foraging may be adopted as a risk minimising strategy when instream macrophyte cover is reduced (Kemp et al., ). Such behaviours, therefore, may represent an optimal strategy to maximise fitness in chalk streams during winter.…”