Noise-induced reduction in the attack rate of a planktivorous freshwater fish revealed by functional response analysis

1. Anthropogenic noise can affect animals physically, physiologically, and behaviourally. Although individual responses to noise are well documented, the consequences in terms of community structure, species coexistence, and ecosystem functioning remain fairly unknown.
2. The impact of noise on predation has received a growing interest and alterations in trophic links are observed when animals shift from foraging to stress-related behaviours, are distracted by noise, or because of acoustic masking. However, the experimental procedures classically used to quantify predation do not inform on the potential demographic impact on prey.
3. We derived the relationship between resource use and availability (the functional response) for European minnows (Phoxinus phoxinus) feeding on dipteran larvae (Chaoborus sp.) under two noise conditions: ambient noise and ambient noise supplemented with motorboat noise. The shape and magnitude of the functional response are powerful indicators of population outcomes and predator–prey dynamics. We also recorded fish behaviour to explore some proximate determinants of altered predation.
4. For both noise conditions, fish displayed a saturating (type II) functional response whose shape depends on two parameters: attack rate and handling time. Boat noise did not affect handling time but significantly reduced attack rate, resulting in a functional response curve of the same height but with a less steep initial slope. Fish exhibited a stress-related response to noise including increased swimming distance, more social interactions, and altered spatial distribution.
5. Our study shows the usefulness of the functional response approach to study the ecological impacts of noise and illustrates how the behavioural responses of predators to noise can modify the demographic pressure on prey. It also suggests that prey availability might mediate the negative effect of noise on predation. Community outcomes are expected if the reduced consumption of the main food sources goes with the overconsumption of alternative food sources, changing the distribution pattern of interaction strengths. Predation release could also trigger a trophic cascade, propagating the effect of noise to lower trophic levels.

     

Influence of acoustics on the collective behaviour of a shoaling freshwater fish

1. Understanding how collective behaviour of animals is influenced by anthropogenic activity is important for their conservation in an increasingly urbanised world. River infrastructure, e.g. for transport and electricity generation, and associated construction and operation, produces sound that can disrupt ecological processes.
2. Adopting a reductionist manipulative experimental approach using Eurasian minnow (Phoxinus phoxinus) as a model shoaling species, we compared the response of individuals and groups of five fish to a broadband acoustic stimulus in a tank containing still water.
3. Four metrics were calculated 10 min immediately before (control–sound stimulus absent) and during the acoustic treatment: (1) swimming speed, (2) persistence of swim paths, (3) cohesion of the group, and (4) orientation of group members.
4. On presentation of the stimulus, groups exhibited a consistent escape response compared to individuals for which behaviour was more variable. Thereafter, individuals swam faster and their swim paths were less persistent than during the control; no difference was observed for groups. Conversely, group integrity became more cohesive and members were more likely to orient in a common direction during the treatment compared to the control.
5. This study provides insight into the importance of collective behaviour of fish in relation to antipredator-like response to anthropogenic noise. Short-term shifts in behaviour are context specific and depend on whether fish are members of a shoal or solitary. The results indicate the potential for negative impacts of unnatural sound on the ecology of shoaling species that inhabit engineered freshwater environments.

     

Consequences of temperature and temperature variability on swimming activity,group structure,and predation of endangered delta smelt

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Behavioural responses to co-occurring threats of predation and ultraviolet radiation in Daphnia

1. Organisms in the wild are faced with multiple threats and a common response is a change in behaviour. To disentangle responses to several threats, we exposed two differently sized species of the freshwater invertebrate Daphnia to solar ultraviolet radiation (UVR) and predation from either moving pelagic or benthic ambush predators.
2. Using an advanced nanotechnology-based method, we tracked the three-dimensional movements of those mm-sized animals at the individual level. Each behavioural trial was performed both under conditions resembling night (no UVR) and day (UVR) and we examined patterns of the depth distribution and swimming speed by Daphnia across three treatments: no predator (control); bottom-dwelling damselfly (Calopteryx sp.); and fish (stickleback, Pungitius pungitius) predators. We also quantified the actual predation rate by the two predators on the two Daphnia species, Daphnia manga and Daphnia pulex.
3. We show that individual Daphnia are able to identify predators with different feeding habitats, rank multiple and simultaneously occurring risks and respond in accordance with the actual threat; complex responses that are generally associated with larger animals.
4. In a broader context, our results highlight and quantify how a cocktail of everyday threats is perceived and handled by invertebrates, which advances our understanding of species distribution in space and time, and thereby of population dynamics and ecosystem function in natural ecosystems.

     

Morphology,metabolism and behaviour: responses of three fishes with different lifestyles to acute hypoxia

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Long-term changes in littoral fish community structure and resilience of total catch to re-oligotrophication in a large,peri-alpine European lake

1. The littoral zone of lakes is used as spawning, shelter, or feeding habitat for many fish species and hence is of key importance for overall lake functioning. Despite this, hardly any studies exist examining the long-term dynamics and response of the littoral fish community, composed mostly of juvenile fish, to environmental change. Here, we study the response of total catch per unit effort (CPUE) and individual species CPUE of such a community to 17 years of oligotrophication and examine whether the species responses can be characterised as synchronous or asynchronous.
2. We analyse a data set of beach seine catches carried out during morning and twilight, late spring and late summer at three sites in large and deep Lake Constance from 1997 to 2014. Generalised additive mixed models were used to explore changes in CPUE of the overall community and of the most frequently occurring species, and Kendall's W test was applied to examine whether the dynamics of fish species were synchronous or asynchronous.
3. Species-specific and total CPUE strongly differed between morning and twilight and between spring and summer indicating an important role of behavioural and life cycle adaptations of species for CPUE. In addition, also the CPUE of some species seeking shelter behind larger stones was lower at sites without these.
4. Total CPUE did not decline suggesting the overall abundance of littoral fish was resilient to declining nutrients. In contrast, fish community composition changed strongly during the study period due to increases in some species (dace, loach, perch) and decreases in others (bream, burbot, chub, ruffe), indicating response diversity of fish to oligotrophication. The type of community dynamics was scale-dependent, whereby significantly synchronous dynamics according to Kendall's W were observed when taking seasonal variability into account. In contrast, significantly asynchronous species dynamics were observed when only the low-frequency variability of species dynamics was considered separately for spring and summer time series.
5. Resilience of littoral fish total CPUE to oligotrophication might have important consequences for ecosystem dynamics and ecosystem services beyond the littoral zone. As small fish often impose strong predation pressure on zooplankton, their resilience might sustain a high top-down control on zooplankton resulting in a further reduction of zooplankton biomass. This could contribute to delayed food web responses and reduced growth of fish with oligotrophication.

     

Parasite‐induced alterations of host behaviour in a riverine fish: the effects of glochidia on host dispersal

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Net cages enhance golden mussel (Limnoperna fortunei) larval density and condition factor

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Pomphorhynchus laevis manipulates Gammarus pulex behaviour despite salt pollution

1. Salt pollution of freshwater ecosystems represents a major threat to biodiversity, and particularly to interactions between free-living species and their associated parasites. Acanthocephalan parasites are able to alter their intermediate host's phenotype to reach final hosts, but this process could be affected by salt pollution, thereby compromising survival of the parasite.
2. We experimentally assessed the impact of salt on the extended phenotype of the parasite Pomphorhynchus laevis in their intermediate host, the amphipod Gammarus pulex, based on three amphipod behaviours: distance covered in flowing water, phototaxis, and geotaxis. We hypothesised that: (1) salt pollution negatively affected the behaviour of uninfected gammarids, and (2) that P. laevis could maintain their capacity to manipulate their host despite this pollution.
3. All three amphipod behaviours were altered by P. laevis: infected G. pulex covered a greater distance, were less photophobic and were more attracted to the water surface than uninfected amphipods, in control or salt-polluted water. However, salinity reduced distance covered in flowing water and increased attraction to the water surface of uninfected and infected G. pulex. For the phototaxis behaviour, P. laevis enhanced this capacity of manipulation in salt-polluted water compared to control water.
4. Pomphorhynchus laevis can still manipulate the behaviour of their intermediate host in salt-polluted water. Acanthocephalan parasites have not been known to be able to manipulate their intermediate host when under pollution stress. Trophic interactions, but not the chances of parasite transmission to their definitive host, appear to be affected by salt pollution.
5. Our study indicates that behavioural modifications induced by complex lifecycle parasites should be more considered in the context of growing concentrations of chemical pollutants in some freshwater ecosystems. Interspecific interactions, and particularly host–parasite relationships, are a key component of ecosystem stability and their alteration could result in major changes in energy flow.

     

No quarter: Lack of refuge during flow intermittency results in catastrophic mortality of an imperiled minnow

1. Many once-perennial rivers have become intermittent. Channel drying can result in fish mortality if refuges are not available. Understanding where refuges occur and if fishes use these refuges can provide insight for species persistence and help stakeholders manage limited resources. Streamflow diversions in the Rio Grande of New Mexico can result in >60 km losses of aquatic habitat, affecting up to 30% of the range of imperiled Rio Grande silvery minnow (Hybognathus amarus). Potential refuges include areas with perennial flow below diversion dams, isolated pools, and irrigation return flows.
2. We examined spatial and temporal patterns of both adult and young-of-year Rio Grande silvery minnow collected in isolated pools that formed during streamflow intermittency from 2009 to 2019. We hypothesised that: (1) Rio Grande silvery minnow would be more numerous in pools that persisted longer; (2) they would be more numerous in isolated pools located closer to upstream areas of perennial flow, due to upstream movement to escape drying; and (3) increased rate of aquatic habitat loss each day would result in more Rio Grande silvery minnow in isolated pools.
3. During the 12 years of the study, we counted Rio Grande silvery minnow in 3,985 isolated pools that formed during streamflow intermittency. We related counts of Rio Grande silvery minnow in each pool to the maximum pool depth, rate of loss of aquatic habitat that occurred that day, and distance each pool was to an upstream barrier. In 2016, we examined persistence of 290 isolated pools until complete desiccation or reconnection with continuous flows occurred, and the factors that influenced pool persistence.
4. Deeper pools persisted for longer, but depth had a small positive effect on counts of adult Rio Grande silvery minnow and no effect on counts of young-of-year in isolated pools. Adults were more numerous in upstream isolated pools, whereas young-of-year were more numerous in downstream isolated pools. Rate of channel drying had little effect on the numbers of adult Rio Grande silvery minnow in isolated pools, but more young-of-year were stranded when the rate of drying was faster. On average, pools persisted <4 days and 263 of 290 dried completely before continuous flows returned. Only 66 of 4,749 Rio Grande silvery minnow occurred in pools that did not dry completely.
5. Rio Grande silvery minnow did not appear to escape channel intermittency; instead, they became stranded in shrinking isolated pools that did not persist long enough to act as refuges for fishes. Lack of refuge during channel intermittency would result in catastrophic mortality of fishes through complete desiccation of pools if there were no management actions, such as translocating fish. To increase persistence through streamflow intermittency, conservation actions should match the species response to intermittency by ensuring the availability of perennial-water refuges at the appropriate spatial and temporal scale.

     

Impact of anthropogenic disturbances on a diverse riverine fish assemblage in Fiji predicted by functional traits

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Effects of Boat Engine Noise on the Auditory Sensitivity of the Fathead Minnow, Pimephales promelas

Fishes are constantly exposed to various sources of noise in their underwater acoustic environment. Many of these sounds are from anthropogenic sources, especially engines of boats. Noise generated from a small boat with a 55 horsepower outboard motor was played back to fathead minnows, Pimephales promelas, for 2 h at 142 dB (re: 1 Pa), and auditory thresholds were measured using the auditory brainstem response (ABR) technique. The results demonstrate that boat engine noise significantly elevate a fish's auditory threshold at 1 kHz (7.8 dB), 1.5 kHz (13.5 dB), and 2.0 kHz (10.5 dB), the most sensitive hearing range of this species. Such a short duration of noise exposure leads to significant changes in hearing capability, and implies that man-made noise generated from boat engines can have far reaching environmental impacts on fishes.     

Interactive effects of road salt and sediment disturbance on the productivity of seven common aquatic macrophytes

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Impacts of co-occurring environmental changes on Alaskan stream fishes

1. Freshwater fishes are now facing unprecedented environmental changes across their northern ranges, especially due to rapid warming occurring at higher latitudes. However, empirical research that examines co-occurring environmental effects on northern fish communities remains limited.
2. We used fish community data from 1587 Alaskan stream sites to examine the potential combined and interacting effects of climate change, current weather, habitat, land use, and fire on two community-level metrics (species richness, relative abundance), and on the distributions of three Alaskan fish species.
3. Our models were 71–76% accurate in predicting the distribution of Alaskan stream fishes using a combination of climate and habitat variables. In contrast to other freshwater ecosystems that are most threatened by land use pressures, we did not detect any evidence for the potential stress of anthropogenic land use or fire on stream fishes.
4. Warming temperatures increased overall community richness and abundance but produced differing responses at the species level. Juvenile salmon presence was positively associated with several climate variables including warmer spring and autumn temperatures and wetter summers. In comparison, warmer seasonal temperatures contributed to declines for northern-adapted species such as Arctic grayling and Dolly Varden.
5. This study highlights the overarching role of current and changing climate in regulating northern stream fish biodiversity. Although many fish species may benefit from climate change across their northern ranges, localised declines are likely to occur and may prove detrimental for communities with limited fishing portfolios. Climate change adaptation and mitigation strategies customised for rapidly changing northern ecosystems will play an essential role in preserving ecologically unique northern species.

     

Multiple lines of evidence reveal complex rainbow trout responses to stream habitat enhancements

1. Habitat enhancements seek to ameliorate the detrimental effects of environmental degradation and take many forms, but usually entail structural (e.g. logs, cribs, reefs) or biogenic (e.g. carrion additions, vegetation plantings, fish stocking) augmentations with the intent of increasing fish annual production (i.e. accrual of new fish biomass through time). Whether efforts increase fish production or simply attract fish has long been subject to debate.
2. Streams of the Pacific Northwest are commonly targeted for habitat enhancements to mitigate for the detrimental effects of dams and other forms of habitat degradation on Pacific salmon. Nutrient mitigation (i.e. the practice of artificially fertilising freshwaters) is a form of biogenic habitat enhancement that attempts to mimic the enrichment effects of a natural Pacific salmon spawning event. This approach assumes nutrient augmentations alleviate nutrient limitation of primary producers and/or food limitation of primary and secondary consumers, culminating in increased fish production.
3. We conducted a multi-year manipulative experiment and tracked responses of interior rainbow trout (Oncorhynchus mykiss) to annual additions of Pacific salmon carcasses as part of an effort to enhance the productivity of salmonid populations in streams where salmon runs have been lost. We employed an integrated approach to partition the mechanisms driving numerical responses of trout populations across timescales, to assess population turnover, and to track responses to habitat enhancements across individual to population level metrics.
4. Short-term numerical increases by trout were shaped by immigration and subsequently via retention of individuals within treatment reaches. As trout moved into treated stream reaches, individuals foraged, grew, and subsequently moved to other locations such that short-term increases in fish numbers did not persist from year to year. All told, additions of salmon carcasses alleviated apparent food limitation and thereby increased secondary production of rainbow trout. However, at an annual time scale, increased production manifested as larger individual fish, not more fish within treated reaches. Fish movements and high population turnover within treated stream reaches apparently led to the subsequent dispersal of increased fish production.
5. We found multiple lines of evidence that indicated that annual additions of salmon carcasses aggregated rainbow trout and enhanced their annual production. Through this replicated management experiment, we documented dynamic individual and population level responses to a form of stream habitat manipulation across weekly and annual timescales.

     

Seasonal variation in the strength of interference competition among headwater stream predators

1. Vertebrate communities in headwater streams are assumed to be regulated through competitive and predatory interactions. Although documented predation is rare, studies regularly report competitive dominance by fish that, as larger competitors reliant on aquatic habitat, exclude semi-aquatic salamanders to marginal stream habitat. However, it is unclear whether fish interact with stream-breeding salamanders through indirect effects such as competition for resources (e.g. food or cover) or fear (i.e. threat of predation) nor is it known whether these interactions are consistent through time.
2. This study used a novel caging approach to determine if competitive outcomes between a headwater fish and salamanders were regulated primarily through resource depletion (exploitative competition) or behavioural avoidance (interference competition).
3. We paired banded sculpin (Cottus carolinae) and larval red salamanders (Pseudotriton ruber) of similar body size in independent flow through mesocosms with intra- and inter-specific pairs allowed to interact physically or non-physically. The experiment was repeated in the autumn and in the spring when stream salamander larvae begin to transform into terrestrial juveniles.
4. Banded sculpin negatively influenced growth of red salamanders regardless of whether they were allowed to physically interact, suggesting interference competition and behavioural avoidance. This asymmetrical effect was strongest in the spring when salamanders underwent metamorphosis at higher rates in the presence of fish. However, in the autumn, the effects were more balanced between the two species with salamanders impacting fish through exploitative competition.
5. By studying the temporal relationships between two competitors and using a caging method novel to competition studies, we established that the outcomes of competition are dependent on season and may vary in type relative to the timing of life-history events. For this community, these results suggest that outcomes of competition are highly dependent on season and could indicate a biotic mechanism maintaining headwater salamander distributions through source–sink dynamics. Our results also suggest that, in this species interaction, it may be unwarranted to assume that the outcomes of competition at one time represent the complex relationships regulating community interactions.

     

Spatial extent of analysis influences observed patterns of population genetic structure in a widespread darter species (Percidae)

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Regional vs local drivers of phylogenetic and species diversity in stream fish communities

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Parasite manipulation of brain monoamines in California killifish (Fundulus parvipinnis) by the trematode Euhaplorchis californiensis

California killifish (Fundulus parvipinnis) infected with the brain-encysting trematode Euhaplorchis californiensis display conspicuous swimming behaviours rendering them more susceptible to predation by avian final hosts. Heavily infected killifish grow and reproduce normally, despite having thousands of cysts inside their braincases. This suggests that E. californiensis affects only specific locomotory behaviours. We hypothesised that changes in the serotonin and dopamine metabolism, essential for controlling locomotion and arousal may underlie this behaviour modification. We employed micropunch dissection and HPLC to analyse monoamine and monoamine metabolite concentrations in the brain regions of uninfected and experimentally infected fish. The parasites exerted density-dependent changes in monoaminergic activity distinct from those exhibited by fish subjected to stress. Specifically, E. californiensis inhibited a normally occurring, stress-induced elevation of serotonergic metabolism in the raphae nuclei. This effect was particularly evident in the experimentally infected fish, whose low-density infections were concentrated on the brainstem. Furthermore, high E. californiensis density was associated with increased dopaminergic activity in the hypothalamus and decreased serotonergic activity in the hippocampus. In conclusion, the altered monoaminergic metabolism may explain behavioural differences leading to increased predation of the infected killifish by their final host predators.