Ecological processes are structured in space and there are important benefits in incorporating spatial information for the analysis of data sets obtained from field studies. Assessing the effect of ...different flow management practices on river ecosystems is an example where such an exercise is highly relevant. Human activities such as hydroelectric power production are known to modify the temporal variability in river flow. Flow management strategies may have a direct influence on fishes and may trigger complex cascades of interactions involving different features of the river ecosystem. In this study, we performed an assessment of the effect of different flow management practices on fish count density (no. fish/m2), biomass density (g/m2), and species richness. Data were collected in 941 sites located along 28 Canadian rivers. These rivers were either naturally flowing or had altered flows from one of three flow management strategies: run of the river dams, storage with gradual release, or storage with peak release. Each site (300 m2) was surveyed using paired snorkeling and electrofishing techniques; environmental variables (water depth and velocity, and substrate composition) were also measured. The study spanned a broad geographic range (3497 km, geodesic distance) and involved repeated local observations (16–50 sites/river), and was therefore inherently spatially organized. We used spatial modeling to obtain a baseline to estimate the effect of flow management strategies on fishes. Our results indicate that rivers downstream of flow peaking storage dams have, by far, the lowest fish densities (count and biomass) and species richness, whereas those downstream of gradual release storage dams had higher fish biomass density than the unregulated rivers.
Within freshwater fishes, closely related species produce alarm cues that are chemically similar, leading to conserved antipredator responses. Similar conservation trends are predicted for species ...with geographically isolated populations. Here, we tested this hypothesis with the guppy (
Poecilia reticulata
Peters, 1859) from two populations within the Aripo River, Trinidad. Free-ranging guppies in the Lower Aripo (high-predation population) exhibited more risk-aversive inspection behaviour towards a fish predator model paired with the alarm cues of guppies collected from the same population versus a river water control. In comparison, when paired with the alarm cues of guppies from the Upper Aripo (low-predation population), the response was intermediate. In the laboratory, we tested Upper and Lower Aripo guppies to the alarm cues of the same or different Aripo River donors, Quaré River guppies (a high-predation population from a different drainage), or a water control. Both Upper and Lower Aripo River guppies exhibited the highest intensity response to donors from the same population and the lowest intensity response to Quaré River donors, with the response to different Aripo donors being intermediate. Collectively, these results demonstrate a trend of intraspecific conservation of chemical alarm cue production, leading to population-specific responses to conspecific cues.
The physiology and behaviour of fish are strongly affected by ambient water temperature. Physiological traits related to metabolism, such as aerobic scope (AS), can be measured across temperature ...gradients, and the resulting performance curve reflects the thermal niche that fish can occupy. We measured AS of westslope cutthroat trout (Oncorhynchus clarkii lewisi) at 5, 10, 15, 20, and 22 °C and compared temperature preference (T
pref
) of the species with non-native brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss). Intermittent-flow respirometry experiments demonstrated that metabolic performance of westslope cutthroat trout was optimal at ∼15 °C and decreased substantially beyond this temperature, until lethal temperatures at ∼25 °C. Adjusted T
pref
across species were comparatively high, ranging from 17.8 to 19.9 °C, with the highest T
pref
observed for westslope cutthroat trout. Results suggest that although westslope cutthroat trout is considered a cold-water species, they do not prefer or perform as well in cold water (≤10 °C) and thus can occupy a warmer thermal niche than previously thought. The metabolic performance curve (AS) can be used to develop species‐specific thermal criteria to delineate important thermal habitats and guide conservation and recovery actions for westslope cutthroat trout.
The physiology and behaviour of fish are strongly affected by ambient water temperature. Physiological traits related to metabolism, such as aerobic scope (AS), can be measured across temperature ...gradients, and the resulting performance curve reflects the thermal niche that fish can occupy. We measured AS of westslope cutthroat trout (Oncorhynchus clarkii lewisi) at 5, 10, 15, 20, and 22 °C and compared temperature preference (T
pref
) of the species with non-native brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss). Intermittent-flow respirometry experiments demonstrated that metabolic performance of westslope cutthroat trout was optimal at ∼15 °C and decreased substantially beyond this temperature, until lethal temperatures at ∼25 °C. Adjusted T
pref
across species were comparatively high, ranging from 17.8 to 19.9 °C, with the highest T
pref
observed for westslope cutthroat trout. Results suggest that although westslope cutthroat trout is considered a cold-water species, they do not prefer or perform as well in cold water (≤10 °C) and thus can occupy a warmer thermal niche than previously thought. The metabolic performance curve (AS) can be used to develop species‐specific thermal criteria to delineate important thermal habitats and guide conservation and recovery actions for westslope cutthroat trout.
Fish rely on both chemical and visual cues to evaluate predation risk. Decisions with respect to activity partitioning in time (i.e., night vs. day) rely on accurate assessment of predation risk ...relative to energy intake;; predation risk is generally thought to be lower at night at the expense of feeding opportunities. At night, the sensory complement model predicts greater reliance on chemical perception of risk. Under this condition, a lower ability to use vision should result in a more conservative response to chemical cues than during the day. We tested this hypothesis under natural conditions by comparing the alarm response of young-of-the-year Atlantic salmon (
Salmo salar
L., 1758) under summer day and night conditions in salmon nursery streams. We found that salmon responded to the alarm cues to a significantly greater extent at night. This suggests that the sensory complement model may be correct and that nocturnal perception of risk may be generally higher than previously believed for juvenile salmon in the wild. In the absence of a more precise indicator of risk (e.g., vision), a greater reliance on chemosensory risk assessment at night may cause fish to shift to more risk-adverse behaviour.
Even at sublethal concentrations, various anthropogenic pollutants may disrupt the transfer of chemosensory information, often inducing maladaptive behavioral responses. Recent studies of freshwater ...prey fishes have shown impaired abilities to respond to damage‐released chemical alarm cues from conspecifics under weakly acidic conditions (pH ∼ 6.0). Several factors acting individually or collectively may account for such chemosensory impairment. By itself, acidification may chemically disrupt the alarm cues and affect fish olfactory functions. Alternatively, differences in local environmental conditions may affect biochemical composition, quantity of chemical alarm cues produced by epidermal tissue, or both, leading to variations in alarm response. Our goal was to assess whether the ability to produce and detect conspecific chemical alarm cues is similar in individuals reared under neutral versus acidic conditions. We conducted two experiments in which we measured the behavioral response of wild juvenile Atlantic salmon Salmo salar exposed to chemical alarm cues. In particular, we looked for differences in the ability of individual fish to (1) produce alarm cues capable of eliciting consistent antipredator behavior in conspecifics and (2) detect alarm cues upon the fish's introduction into a stream with a pH differing from that of the stream of origin; the latter experiment involved reciprocal transplant of fish between neutral (pH range ∼ 7.0–7.3) and acidic (pH range ∼ 5.9–6.3) sites. Our results demonstrate that the ability to produce and respond to chemical alarm cues is maintained in Atlantic salmon reared under acidic conditions and did not differ from that of fish reared under neutral conditions. Overall, these data suggest that no permanent olfactory damage occurred under reduced pH and, likewise, no significant difference in functional alarm cue production existed between Atlantic salmon reared under neutral and acidic conditions. Short‐term reduction in olfactory sensitivity and degradation of the chemical alarm cues under acidic conditions are the likely mechanisms affecting detection of these important chemicals by prey fish.
Predation is a strong selective force acting on prey animals. Predation is by nature highly variable in time; however, this aspect of predation risk has traditionally been overlooked by behavioural ...ecologists. Lima and Bednekoff proposed the predation risk allocation hypothesis (RAH), predicting how temporal variation in predation risk drives prey antipredator behaviours. This model is based on the concept that prey adaptively allocate their foraging and antipredator efforts across high- and low-risk situations, depending on the duration of high- vs. low-risk situations and the relative risk associated with each of them. An unstudied extension of the RAH is the effect of predictability of predation risk. A predictable risk should lead to prey displaying minimal vigilance behaviours during predictable low-risk periods and the strongest antipredator behaviours during risky periods. Conversely, an unpredictable predation risk should result in prey displaying constant vigilance behaviour, with suboptimal foraging rates during periods of safety but antipredator behaviours of lower intensity during periods of risk. We tested this extension of the RAH using convict cichlids exposed to high-risk alarm cues at two frequencies of risk (1x vs. 3x) per day, on either a fixed or random schedule for 5 d. We then tested the fish for a response to high-risk cues (alarm cues) and to low-risk cues (disturbance resulting from the introduction of distilled water). Our study supports previous results on the effects of risk frequency and cue intensity on cichlid behaviour. We failed to show an effect of risk predictability on the behavioural responses of cichlids to high-risk alarm cues, but predictability did influence responses to low-risk cues. We encourage further studies to test the effect of predictability in other systems.
Interdisciplinary approaches are required to tackle complex environmental issues as freshwater ecosystems face unprecedented pressures globally. The emerging Ecohydraulics field of research should, ...therefore, take steps towards developing true interdisciplinarity to adapt to a continuing changing world. This study contributes to the ongoing discussion on interdisciplinarity in Ecohydraulics and shapes its growth by identifying key actions, actors and implementation strategies that can strengthen it. Based on an online questionnaire and a workshop involving over 150 early and established careers, we present a list of 20 prioritised actions that will help engage the research community towards specific goals and will result in increased interdisciplinary outcomes. While early career researchers (ECRs) have taken the lead on creating this roadmap, its implementation should be a joint responsibility of both ECRs, established career scientists, groups, and institutions within Ecohydraulics. The list of identified actions and assigned responsibility should, therefore, be considered a conversation starter. Continued revision of the here-stated approaches will be required in the future as the field of research and its community progresses. With this contribution, we resume a critical reflection on where the Ecohydraulics field of research and community stand today and suggest where resources should be invested in the long-term to consolidate the inherent interdisciplinarity in Ecohydraulics.
The assessment of predation risk is crucial to the survival of a prey individuals and the ability to gauge risk accurately will consequently be shaped by a suite of behavioural trade-offs. In ...salmonids, risk may be assessed through the detection of damage-released chemical cues. When these chemical cues are paired with a novel odour, covert antipredator responses are elicited upon subsequent exposure to the novel odour and learning occurs. My research focuses on the retention of newly acquired information (lemon odour), through sequential exposure to this same novel odour in both laboratory- reared and wild populations of juvenile Atlantic salmon ( Salmo salar ). Laboratory and field experiments consisted of a single conditioning day (AC + NO) followed by three recognition days (NO), in which antipredator responses were measured from the change in behaviour observed between the five minute pre-stimulus and post-stimulus observation periods. Significant short-term antipredator responses in the laboratory population were observed at the conditioning day, while they were absent at all subsequent recognition days. In particular, the foraging rate and the time spent moving decreased in response to the alarm cue treatment at the conditioning phase, but responses were not significantly different between treatments during any of the succeeding recognition phases. These results suggest that fish respond immediately and overtly to chemical cues, but may treat the information as irrelevant without subsequent exposure to the pairing of chemical cues with a novel odour. Conversely, my field experiment failed to confirm the laboratory results. Further work is required to elucidate any ecological processes that affect the learning mechanism in the current experiments.
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