25 research outputs found
Behavioural and fitness effects of translocation to a novel environment: Wholeâlake experiments in two aquatic top predators
Translocation into a novel environment through common fisheries management practices, such as fish stocking, provides opportunities to study behavioural and fitness impacts of translocations at realistic ecological scales. The process of stocking, as well as the unfamiliarity with novel ecological conditions and the interactions with resident fish may affect translocated individuals, leading to alterations of behaviours and causing fitness impacts.
Our objectives were to investigate how aquatic top predators behaviourally establish themselves and compete with resident individuals following introduction in a novel lake environment and to investigate the resulting fitness consequences.
Using highâresolution acoustic telemetry, we conducted wholeâlake experiments and compared the activity, activityâspace size and fate of translocated and resident individuals in two model top predators, the northern pike Esox lucius (n = 160) and European catfish Silurus glanis (n = 33). Additionally, we compared the reproductive success of translocated and resident northern pike. The experiment was conducted with large (adult) individuals of different origins, resilient to predation, but subject to agonistic interactions and competition with resident fish.
Over a period of several months, the translocated catfish exhibited consistently larger activityâspace sizes than resident catfish, but did not differ from residents in activity and survival. The pike from one of the two translocated origins we tested also showed elevated spaceâuse, and both translocated origins revealed higher mortality rates than their resident conspecifics, indicating maladjustment to their novel environment. When nonâresident pike reproduced, they overwhelmingly produced hybrid offspring with resident fish, indicating that introductions fostered gene flow of nonânative genes.
Our study indicates that fish introductions result in behavioural and fitness impacts even in largeâbodied top predators that experience low levels of natural predation risk.Leibniz CommunityBesatzfisch (German Federal Ministry for Education and Research)Peer Reviewe
Positioning aquatic animals with acoustic transmitters
Geolocating aquatic animals with acoustic tags has been ongoing for decades, relying on the detection of acoustic signals at multiple receivers with known positions to calculate a 2D or 3D position, and ultimately recreate the path of an aquatic animal from detections at fixed stations.This method of underwater geolocation is evolving with new software and hardware options available to help investigators design studies and calculate positions using solvers based predominantly on time-difference-of-arrival and time-of-arrival.We provide an overview of the considerations necessary to implement positioning in aquatic acoustic telemetry studies, including how to design arrays of receivers, test performance, synchronize receiver clocks and calculate positions from the detection data. We additionally present some common positioning algorithms, including both the free open-source solvers and the 'black-box' methods provided by some manufacturers for calculating positions.This paper is the first to provide a comprehensive overview of methods and considerations for designing and implementing better positioning studies that will support users, and encourage further knowledge advances in aquatic systems
A lake as a microcosm: reflections on developments in aquatic ecology
In the present study, we aim at relating Forbes' remarkable paper on "The lake as a microcosm", published 125 years ago, to the present status of knowledge in our own research group. Hence, we relate the observations Forbes made to our own microcosm, Lake Krankesjon in southern Sweden, that has been intensively studied by several research groups for more than three decades. Specifically, we focus on the question: Have we made any significant progress or did Forbes and colleagues blaze the trail through the unknown wilderness and we are mainly paving that intellectual road? We conclude that lakes are more isolated than many other biomes, but have, indeed, many extensions, for example, input from the catchment, fishing and fish migration. We also conclude that irrespective of whether lakes should be viewed as microcosms or not, the paper by Forbes has been exceptionally influential and still is, especially since it touches upon almost all aspects of the lake ecosystem, from individual behaviour to food web interactions and environmental issues. Therefore, there is no doubt that even if 125 years have passed, Forbes' paper still is a source of inspiration and deserves to be read. Hence, although aquatic ecology has made considerable progress over the latest century, Forbes might be viewed as one of the major pioneers and visionary scientists of limnology
Behavioural and fitness consequences of direct and indirect non-lethal disturbances in a catch-and-release northern pike ( Esox lucius
In a catch-and-release recreational fishery fish populations can be impacted by lethal
and sub-lethal effects. In terms of sub-lethal effects anglers may directly
(catch-and-release) and/or indirectly (angling-related disturbances, e.g.
boating) influence the behaviour, growth and fitness of the fish. We quantified
the long-term behavioural response of northern pike Esox lucius to
angler-induced direct and indirect disturbances using radio-telemetry techniques. A whole
lake experimental approach was conducted by dividing the study lake into an
angling-disturbed and an angling-undisturbed lake side with 10 radio-tagged fish on each
side, representing ~20% of the adult pike population. The impact of angling-caused
disturbances on pike behaviour and growth as a proxy for fitness was assessed in a 7 month
study period. Direct disturbances reduced swimming activities of pike and resulted in
increased selection for structured (i.e., safer) habitat, whereas
indirect disturbances had no significant effect on pike behaviour. Growth rates of
caught-and-released fish were significantly smaller than those of uncaught pike (44%).
Because, fish that were not captured by angling during the study period showed similar
growth rates on both sides of the lake, this indicated that only direct angler-induced
disturbances influenced pike growth. Our findings call for minimization of angling-related
stressors during the process of catch-and-release angling to avoid behavioural and fitness
impairments of the released fish because these may ultimately have population-level
effects
Site fidelity and seasonal changes in activity centre size of female pike Esox lucius in a small lake
Seasonal and diurnal patterns of littoral microhabitat use by fish in gravel pit lakes, with special reference to supplemented deadwood brush piles
The habitat quality of the littoral zone is of key importance for almost all lentic fish species. In anthropogenically created gravel pit lakes, the littoral zone is often structurally homogenized with limited fish habitats. We supplemented deadwood brush piles in the littoral zone of eight gravel pit lakes and investigated the diurnal and seasonal use of this and other typical microhabitats by six dominant fish species. Shoreline habitats were sampled using point abundance electrofishing during day and night in all four seasons, and patterns of fish abundance were compared amongst unstructured littoral habitats, emerged macrophytes and brush piles. We caught a total of 14,458 specimens from 15 species in the gravel pit lakes. Complex shoreline structures were used by all fish species that we examined, especially during daytime, whilst the use of unstructured habitats was highest during night. The newly added brush piles constituted suitable microhabitats for selected fish species, perch (Perca fluviatilis), roach (Rutilus rutilus) and pike (Esox lucius), particularly during winter. Supplemented deadwood provides suitable fish habitat in gravel pit lakes and may to some degree compensate for the loss of submerged macrophytes in winter by offering refuge and foraging habitat for selected fish species
Socially induced stress and behavioural inhibition in response to angling exposure in rainbow trout
The battle between harvest and natural selection creates small and shy fish
Harvest of fish and wildlife, both commercial and recreational, is a selective force that can induce evolutionary changes to life history and behavior. Naturally selective forces may create countering selection pressures. Assessing natural fitness represents a considerable challenge in broadcast spawners. Thus, our understanding about the relative strength of natural and fisheries selection is slim. In the field, we compared the strength and shape of harvest selection to natural selection on body size over four years and behavior over one year in a natural population of a freshwater top predator, the northern pike (Esox lucius). Natural selection was approximated by relative reproductive success via parentâoffspring genetic assignments over four years. Harvest selection was measured by comparing individuals susceptible to recreational angling with individuals never captured by this gear type. Individual behavior was measured by high-resolution acoustic telemetry. Harvest and natural size selection operated with equal strength but opposing directions, and harvest size selection was consistently negative in all study years. Harvest selection also had a substantial behavioral component independent of body length, while natural behavioral selection was not documented, suggesting the potential for directional harvest selection favoring inactive, timid fish. Simulations of the outcomes of different fishing regulations showed that traditional minimum size-based harvest limits are unlikely to counteract harvest selection without being completely restrictive. Our study suggests harvest selection may be inevitable and recreational fisheries may thus favor small, inactive, shy, and difficult-to-capture fish. Increasing fractions of shy fish in angling-exploited stocks would have consequences for stock assessment and all fisheries operating with hook and line.This work was supported by the Adaptfish (Leibniz-Community) and Boddenhecht grants (European Maritime and Fisheries Fund of the European Union and the State of Mecklenburg-Vorpommern, Grant MV-I.18-LM-004, B 730117000069) received by R.A. We are grateful to Alexander TĂŒrck, Jan Hallermann, Andreas MĂŒhlbradt, and many other technicians and students for help in the field and processing the data and reviewers for excellent feedback. The experiments and telemetry work were approved through animal care permits (23-2347-15-2010) granted by the Brandenburg State Office of Environment, Health and Consumer Protection
Ecosystem-based management outperforms species-focused stocking for enhancing fish populations
Ecosystem-based management is costly. Therefore, without rigorously showing that it can outperform traditional species-focused alternatives, its broad-scale adoption in conservation is unlikely. We present a large-scale replicated and controlled set of whole-lake experiments in fish conservation (20 lakes monitored over 6 years with more than 150,000 fish sampled) to examine the outcomes of ecosystem-based habitat enhancement (coarse woody habitat addition and shallow littoral zone creation) versus a widespread, species-focused alternative that has long dominated fisheries management practice (i.e., fish stocking). Adding coarse woody habitats alone did not, on average, enhance fish abundance, but creating shallow water habitat consistently did, especially for juvenile fish. Species-focused fish stocking completely failed. We provide strong evidence questioning the performance of species-focused conservation actions in aquatic ecosystems and instead recommend ecosystem-based management of key habitats