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Anthropogenic infrastructure in rivers (e.g. culverts, dams and weirs) can block the movements of fish and negatively impact their communities. Recent research has shown that fish passage at such barriers can be improved through the use of cylindrical bristle cluster (CBC) arrays. The relationship between the hydrodynamic environment created by different CBC array geometries and passage efficiency, the number of fish that passed as a percentage of those that attempted to do so, and swimming behaviour of a native wide spread European cyprinid species, the roach (Rutilus rutilus), was investigated. Passage efficiency was a function of cluster diameter and spacing; efficiency was highest (>80%) when the ratio of lateral cluster spacing (centre to centre) (Sc) to diameter was less than 5. Fish exhibited a range of swimming behaviours while manoeuvring through the CBC array to ascend the weir, the most common of which was zigzagging between two lines of clusters. Additionally, fish utilised lower velocity areas when swimming through a CBC array, often combining different swimming behaviours to successfully navigate at burst speeds. Fish passage efficiency can be improved by increasing the size of the wake behind clusters and the overall hydraulic resistance created within the array while ensuring sufficient space is available for fish to manoeuvre. [ABSTRACT FROM AUTHOR]

The strong association with visual cues exhibited by fish that prefer to inhabit flowing water (rheophilic species) may help reduce the energetic costs of maintaining position due to the provision of spatial points of reference. If this "Station Holding Hypothesis" is true, a positive relationship between the association with visual cues and flow velocity is expected. This hypothesis was tested experimentally by quantifying the response of common minnow (Phoxinus phoxinus) and brown trout (Salmo trutta) to visual cues under three flow velocities. In contradiction to the prediction, there was no evidence that the association with strong visual cues was positively related to flow velocity when fish were presented with vertical black stripes in an open channel flume, although interspecific variation in response was observed. The association with visual cues was relatively weak in trout, compared to minnow that spent 660% more time associated with the zone in which visual cues were present during the treatment, than the control when visual cues were absent. Trout tended to be more exploratory and made short visits to the area where visual cues were present, whereas minnow associated with the cues for longer. The strong association with visual cues independent of flow velocity exhibited by minnow and the weak association across all velocities by trout suggest that this behaviour is unlikely to reflect a strategy to minimise the energetic cost of maintaining position in flowing water. Minnow may have used the visual cues as a proxy indicator of physical structure that provides alternative benefits, such as refuge from predators. Trout may have employed alternative cues (e.g. mechanosensory) to seek more energetically favourable regions of the experimental area, reducing the importance of stationary visual stimuli. [ABSTRACT FROM AUTHOR]

Groundwater‐fed rivers, such as the chalk streams of southern England, exhibit high levels of stability (e.g. flow and temperature) and physical homogeneity (e.g. depth and substrate grain size). However, growth of instream macrophytes is highly variable depending on season, providing an important but ever‐changing source of cover for stream‐dwelling salmonids, such as brown trout (Salmo trutta).In this study, the behavioural ecology of brown trout inhabiting a chalk stream was assessed during periods that included summer and winter. In a reach of the River Lambourn (Berkshire, UK), a combination of physical habitat mapping, electric‐fishing, passive integrated transponder and radio telemetry was used to quantify trout: (1) density relative to physical and thermal characteristics; (2) movement patterns; and (3) performance, in terms of growth.Trout density was positively related to depth during winter (February) and spring (May), but not at the end of summer (September). Despite no statistical relation between trout density and macrophytes, periods of strong and no association between density and depth coincided with sparse and extensive macrophyte cover throughout the study reach, respectively.Despite being greater for some fish in winter compared to summer, the daily distance moved was generally low (<3.5 m/day). While growth was mostly positive, less mass was gained, and performance deviated farther from optimal levels predicted by a growth model, during periods that included winter.A number of factors probably contributed to lower growth in winter, including costs of reproduction, temperatures—which deviated farther from those optimal for growth—and/or an inability to maximise energy intake, e.g. due to time spent holding position in deeper areas as cover provided by macrophytes declined.Despite the lack of extremes in chalk stream environments, the behavioural ecology of brown trout appears to be influenced by seasonal variation in instream cover provided by macrophytes. This emphasises the importance of balancing the management (e.g. cutting and removal) of macrophytes with the ecological benefits they provide. [ABSTRACT FROM AUTHOR]

Culverts used to convey river water under roads and embankments are one of the most common small-scale barriers to longitudinal fish movements worldwide. Using an open channel flume, this study assessed the ability of upstream migrating adult river lamprey (Lampetra fluviatilis) to ascend a pipe culvert when unmodified (control [C]) and retrofitted with spoiler baffles (treatment [T]) under three flow regimes (low discharge [L], high discharge [H] and high discharge with a raised downstream water level [HD]). Few lamprey attempted to ascend the culvert under low (11%) and high (21%) discharge in both the control and the treatments. Despite a greater percentage attempting to pass (75%) under HD, they frequently failed. Contrary to our predictions, upstream progress was impeded by the spoiler baffles and may reflect low motivation or avoidance of the physical and/or hydraulic conditions encountered. This study emphasizes the need to better understand the factors influencing the behaviour and motivation of fish as they ascend fish passage structures, and of the importance of reporting negative results as fish passage solutions that are promising for some species may be ineffective for others. [ABSTRACT FROM AUTHOR]

1. 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. 2. 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. 3. 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. 4. 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. 5. 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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Impact of a small-scale hydropower device on downstream moving fish was assessed. [•] Blade strike was related to fish length, swimming speed, and blade rotational speed. [•] Strike increased and decreased for trout and eel when behaviour was considered. [•] A pinch point created by the hydropower device caused damage to euthanised fish. [•] A field study supported observations from flume experiments and blade strike models. [ABSTRACT FROM AUTHOR]

To mitigate negative impacts of delayed migration it is necessary to understand the causes of avoidance exhibited by animals at behavioural barriers. For downstream migrating juvenile salmon, avoidance of velocity gradients at anthropogenic structures may compromise fitness. Building on previous experimental investigations on salmonid response to velocity gradients, this study aimed to quantify impacts of behaviour on subsequent passage in the presence and absence of visual cues. In an experimental flume, downstream moving juvenile Chinook salmon, Oncorhynchus tshawytscha, encountered either a high or a low velocity gradient created by an orifice weir, under light (95lx) or dark (infrared illumination only) conditions. The majority of fish exhibited an observable response on encountering accelerating velocity, with avoidance behaviour elevated when light (45%) in comparison to when dark (12%). More time was spent facing the flow when the velocity gradient was high. Fish that exhibited avoidance were delayed by approximately eight-fold, travelled 3.5 times further, and experienced a higher mean cumulative velocity gradient across the body length (spatial velocity gradient) prior to successful downstream passage. This study highlights the impact of variation in behaviour on fish passage, and the potential for combined multimodal signals (in this instance visual and mechanosensory) to be used to repel fish, for example from hazardous areas such as turbine intakes. Conversely, by limiting information available, undesirable delay, for example at entrances to downstream fish bypasses, may be reduced. [Copyright &y& Elsevier]

Abstract: Avoidance of abrupt accelerations of flow exhibited by downstream migrating fish at screens used to divert them, or at fishway entrances, can cause delay and adversely impact efficiency. The use of alternative stimuli to attract fish and mask the unwanted deterrent effects associated with velocity gradients is of interest to those working in fish passage engineering. The influence of a continuous light source on the downstream movement of brown trout (Salmo trutta) as they encountered accelerating velocities created by a constricted channel in an experimental flume under three discharge regimes was assessed. It was predicted that: (1) in the absence of a light source, behavioural responses typical of downstream moving salmonids would be elicited on encountering velocity gradients, and that these responses would be initiated at some threshold spatial velocity gradient relative to body length and (2) light would act as an attractant and mask the deterrent effects of a velocity gradient and thus reduce delay. Typical avoidance behaviours, e.g. rheotactic switches in orientation or retreating upstream before re-approaching a velocity gradient, were common. The spatial velocity gradient threshold at which a response was initiated when dark was similar (ca. 0.4cms−1 cm−1) independent of discharge. Fish responded farther upstream at a lower spatial velocity gradient threshold (ca. 0.2cms−1 cm−1) in the presence of both mechanosensory and visual cues when light. Contrary to the second prediction, downstream movement was further delayed by the addition of a light stimulus. The findings support an alternate hypothesis, that responsiveness (avoidance) can be enhanced when multimodal stimuli are presented. [Copyright &y& Elsevier]

Artificial light at night (ALAN) is considered one of the most pervasive forms of environmental pollution. It is an emerging threat to freshwater biodiversity and can influence ecologically important behaviours of fish. The European eel (Anguilla anguilla) is a critically endangered catadromous species that migrates downstream to the ocean to spawn in the Sargasso Sea. Given the pervasive nature of ALAN, many eel will navigate through artificially lit routes during their seaward migration, and although considered negatively phototactic, their response has yet to be quantified. We investigated the response of downstream moving European eel to simulated ALAN using a Light Emitting Diode unit in an experimental flume. We presented two routes of passage under: (1) a dark control (both channels unlit), (2) low ALAN (treatment channel lit to ca. 5 lx), or (3) high ALAN (treatment channel lit to ca. 20 lx). Eel were: (i) more likely to reject an illuminated route when exposed to high levels of ALAN; (ii) less likely to select the illuminated channel when given a choice; and (iii) passed downstream more rapidly when the illuminated route was selected. This study quantified the response of the critically endangered European eel to ALAN under an experimental setting, providing the foundations for future field based research to validate these findings, and offering insight on the ecological impacts of this major environmental pollutant and driver of global change. Image 1 • An experiment assessed the impact of ALAN on a critically endangered fish. • Fish behaviour was affected by ALAN. • Individuals were less likely to select to pass an illuminated route when given the choice. • Individuals passed downstream faster when the illuminated route was selected. Eel more frequently rejected a route when exposed to simulated light pollution, were less likely to select the illuminated route given a choice and passed faster when the illuminated route was selected. [ABSTRACT FROM AUTHOR]

Globally, gauging weirs are commonly installed in rivers to monitor flows. They have widespread negative impacts on the upstream movement of fish due to the barriers created by the unfavourable hydraulic conditions on the downstream face. There is a need to develop simple low-cost solutions to enhance multi-species fish passage, while not impacting the ability of these structures to gauge flow or increasing their potential to accumulate debris. This study investigated the use of an array of Cylindrical Bristle Clusters (CBCs), mounted on the downstream face of Crump weirs, to improve upstream passage of multiple species of fish while maintaining gauging accuracy. The simplicity and modularity of the design helps improve cost effectiveness and ease of installation. Laboratory tests with roach (Rutilus rutilus) showed that the passage efficiency of a Crump weir was increased from 0% (control) to ≈30% when retrofitted with CBCs. Swim path analysis indicated fish utilised low velocity zones in the wake of clusters to facilitate passage. Time taken to pass the weir and length of the swim path were greatest under the highest cluster density, where manoeuvrability was most constrained. Following these promising experimental results, the fish pass efficiency of a weir retrofitted with a staggered array of CBCs, was evaluated in the field. Upstream passage of a number of non-salmonid fish, including chub (Squalius cephalus) and roach, was monitored using Passive Integrated Transponder telemetry at a 7 m long, 1.2 m wide, Crump weir with a 1:5 downstream slope. Overall passage efficiency, considering all species, increased from 2% to 14% when the fish pass was installed, and for chub from 0 to 52%. Debris accumulation was minimal during the test period. Assessment of the impact of a variety of CBC array densities on gauging was also undertaken. As predicted using theory, there was no effect on gauging when arrays were placed downstream of the point at which flow regime changes from sub- to supercritical. This study highlights the potential for a staggered array of CBCs to improve the upstream passage of multiple species of fish at gauging weirs, common barriers to fish migration throughout the world, without affecting the accuracy of flow gauging. [ABSTRACT FROM AUTHOR]

Abstract: Behavioural devices that attract or deflect migrating fish to preferred routes are used to enhance the efficiency of mechanical structures (e.g. screens at turbine and other intakes) or as an alternative to them when their application is deemed unviable. Fish response to stimuli (signals) encountered, and consequently the efficiency of these behavioural devices, can be highly variable. To further develop efficient behavioural screens and fish pass technology there is a need for a generic framework to (1) better understand fish response to environmental stimuli and causes of variation, and (2) quantify ability to detect stimuli and respond in a way deemed appropriate from a management perspective. This paper considers application of signal detection theory (SDT) to fish passage research, using downstream migrating juvenile salmonids as a model. Support is provided in the scientific literature for two key assumptions, that downstream migrants are able to exhibit volitional behaviour in response to stimuli encountered and that these behaviours can be interpreted by an observer to indicate the detection of a signal. Re-evaluation of available data highlights the temporal variability of decision making and elicitation of behaviour within and between individuals, and that sensitivity (d′), a measure of the ability to detect a signal (e.g. hydraulic gradient), increases with signal strength and when multimodal stimuli are presented. SDT is likely to provide a useful “first base” for understanding and quantifying fish behaviour in the development of screens and fish passes. [Copyright &y& Elsevier]