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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.

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 high-resolution acoustic telemetry, we conducted whole-lake experiments and compared the activity, activity-space 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 activity-space 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 space-use, and both translocated origins revealed higher mortality rates than their resident conspecifics, indicating maladjustment to their novel environment. When non-resident pike reproduced, they overwhelmingly produced hybrid offspring with resident fish, indicating that introductions fostered gene flow of non-native genes. Our study indicates that fish introductions result in behavioural and fitness impacts even in large-bodied top predators that experience low levels of natural predation risk., (© 2020 The Authors. Journal of Animal Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.)

Small lakes largely outnumber large lakes among the world's lentic ecosystems. Despite being common landscape elements, however, little is known about the value small lakes provide to recreationists. This paper presents results of an economic valuation study concerned with small gravel pits in Lower Saxony, Germany. Gravel pits are artificially created lake ecosystems that, particularly in Europe, are regularly used and managed by privately organized recreational anglers in an angling club context. A stated choice experiment provided insights into anglers' preferences for the abundance of target fish species, biodiversity of taxa other than fishes in the lakes as well as in the lake surroundings, and about the use of gravel pits by other recreationists for walking, swimming or boating. Latent class analysis identified five segments that varied in preferences. For the majority of anglers, the value of angling at gravel pit lakes was improved by an increase in the abundance of predatory fishes. Additionally, the presence of aquatic and terrestrial endangered species at the lakes increased the value of the ecosystems as perceived by the majority of anglers. By contrast, the presence of other recreational uses reduced the value of angling, with swimming being considered the most disturbing, while the degree of shoreline development had the least impact on the recorded choices. The results suggest that managing the gravel pit lakes for high biodiversity and the presence of desired game fish species maximizes the value for anglers. However, also two smaller segments with anglers revealing lexicographic preferences were identified. These anglers expressed either strong preferences against swimming in the lakes or strongly preferred the opportunity to use boats. Lake management may address the preference heterogeneity and the aversion against other recreational uses, such as swimming, by spatial zoning., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Gravel pit lakes are novel ecosystems that can be colonized by fish through natural or anthropogenic pathways. In central Europe, many of them are managed by recreational anglers and thus experience regular fish stocking. However, also unmanaged gravel pits may be affected by stocking, either through illegal fish introductions or, occasionally, by immigration from connected water bodies. We sampled 23 small (< 20 ha) gravel pit lakes (16 managed and 7 unmanaged) in north-western Germany using littoral electrofishing and multimesh gillnets. Our objective was to compare the fish biodiversity in gravel pit lakes in the presence or absence of recreational fisheries. Given the size of the sampled lakes, we expected species poor communities and elevated fish diversity in the managed systems due to regular stocking of game fish species. Our study lakes were primarily mesotrophic and did not differ in key abiotic and biotic environmental characteristics. Lakes of both management types hosted similar fish abundances and biomasses, but were substantially different in terms of fish community structure and species richness. Fish were present in all lakes, with a minimum of three species. Higher α-diversity and lower β-diversity was discovered in managed gravel pit lakes compared to unmanaged lakes. Consequently, recreational-fisheries management fostered homogenization of fish communities, by stocking a similar set of fish species desired by anglers such as piscivorous fish and large bodied cyprinids. However, unmanaged gravel pit lakes were also affected by human-mediated colonization, presumably by illegal fish releases. Hardly any non-native species were detected, suggesting that recreational-fisheries management did not foster the spread of exotic species in our study region., (© 2019 The Fisheries Society of the British Isles.)

The trophic niche of aquatic generalist predators is influenced by ontogeny, habitat characteristics, availability and type of prey, and competitive interactions. Many interrelated lake characteristics influence the availability of prey and may thereby impact foraging niches and the trajectory of ontogenetic niche shifts. Our work uses Eurasian perch (Perca fluviatilis) as a model species to examine the correlation of multiple lake and fish community characteristics with the size‐dependency of perch populations' realised trophic niche. We used carbon and nitrogen stable isotopes to correlate the changes in perch trophic position across a gradient of total lengths in seven gravel pit lakes that differed in lake morphology, habitat heterogeneity, productivity, structural complexity, and fish community composition. Perch populations in lakes with more shallow‐water habitat reached a higher trophic position at smaller sizes than perch in deeper lakes. However, the changes in trophic position with increasing size were less pronounced compared to perch from deeper lakes. Large individuals from the latter perch populations ultimately achieved higher mean trophic positions compared to fish from shallow lakes. Perch in lakes with more shallow‐water habitat may, therefore, achieve lower rates of piscivory because of higher relative availability of macroinvertebrates or greater competition with zooplanktivores. Our results suggest that large, piscivorous perch are more likely to develop in deeper lakes, and that these changes in perch trophic position across ontogeny are more strongly related to the depth of lakes than to the type of structured habitat in the littoral zone. [ABSTRACT FROM AUTHOR]

Gravel pit lakes are common across Europe. These novel ecosystems serve as model systems to study human‐induced and natural colonisation of isolated lakes by fish. Fisheries‐management activities can quickly spread species over large distances, possibly homogenising fish communities across ecosystems, while fostering local fish diversity.Our objective was to evaluate the effects of lake genesis (gravel pit lakes < 100 years old vs. natural lakes of glacial genesis ~10,000 years old) and fisheries management (fish stocking activities present vs. absent) on the fish community in small lakes, while controlling for key environmental variables known to affect lake fish communities.We sampled fish communities by electrofishing and multimesh gillnetting in 47 isolated lakes managed for fisheries, and 19 unmanaged and isolated lakes of both natural and artificial origin in northern Germany. Unmanaged lakes were used as reference to assess fisheries‐management impacts in small natural and artificial lakes.We caught 178,506 fish from 30 species and found that the accumulation of native lake fish species in lakes was associated with fisheries management, which increased local species richness (α‐diversity) and number of predatory species, and reduced among‐lake variation in fish community composition (β‐diversity; i.e., homogenisation). The homogenisation‐effect associated with fisheries happened with introduced native fish species, whereas non‐native species were rarely detected.In unmanaged gravel pit lakes, the littoral fish community composition was substantially different to the communities present in both types of managed lakes and unmanaged natural lakes. Therefore, the relatively young unmanaged gravel pit lakes revealed evidence of ongoing, stochastic colonisation processes that resulted in comparatively species‐poor fish communities.We concluded that fisheries management by anglers speeds up the colonisation of gravel pit lakes with native fish species in the study area. For planning initial fish introductions in newly created gravel pit lakes, it is recommended that fish communities from ecologically similar natural lakes within the same geographical region are used as references to maintain the biotic integrity of newly created fish communities. [ABSTRACT FROM AUTHOR]

Small lakes provide substantial ecosystem services to society, particularly recreational services. These ecosystem services are rarely quantified. It is also unclear whether expectations about desired lake attributes by various user groups and the public at large align. In many landscapes most small lakes artificially originate from sand and gravel mining along highways and close to cities. Using a choice experiment, in samples from north-western Germany we quantified the ecological services provided by these so-called gravel pit lakes and investigated potential conflicts among the preferences of the public and anglers as a specific user group. The same visual choice sets were employed to assess the preferences for different recreational services as well as biodiversity attributes. We also tested whether the presence of anglers at the small gravel pit lakes affected how people from the public valued the services provided by the lakes. Both the public and the anglers valued the presence of endangered fish species and endangered other taxa positively, suggesting that improved conservation of biodiversity would benefit all users. The public and anglers varied in relation to the recreational uses desired at gravel pit lakes. The opportunity to swim was valued positively by the public and negatively by the surveyed anglers. Yet, the presence of anglers did not significantly reduce the value assigned to gravel pit lakes by the public, suggesting the co-existence of anglers and swimmers would be possible. Co-existence could be fostered through establishing separate angling and swimming zones. Our work suggests the presence of local trade-offs in the management of small gravel pit lakes, specifically between swimmers and anglers. However, conservation of endangered species constitutes a common goal that suits the expectations of all. [ABSTRACT FROM AUTHOR]

Protected areas are a common management tool to conserve habitats and species by controlling access and disturbances by humans. Whenever protected areas result in restricting access to riparian zones in lakes, they may have positive effects on habitats and taxa beyond fish by lowering influences of trampling or boating on plants, by reducing the degree of human-induced disturbances to sensitive taxa such as birds, and by reducing fishing effort. However, especially in small freshwater systems knowledge about the functioning of protected areas that cover only parts of the lake shorelines is limited. We studied small gravel pit lakes in Germany where recreational fishing clubs have voluntarily assigned no-access riparian protected areas on parts of the lake shorelines and examined outcomes for habitat quality, plants, fish and bird populations. A total of 15 lakes were sampled, and we assessed habitat structure and abundance of plants, and fish within and outside protected areas and bird abundance at the lake scale, relying on standardized sampling methods. After controlling for confounding environmental factors related to lake morphology, age, nutrients, and land use, we detected positive contributions of small-scale riparian protected areas on habitat structure, riparian vegetation, local fish abundance and abundance of sensitive songbirds at the lake-scale, but we found no effects on aquatic vegetation and on disturbance-sensitive waterfowl species. Scale-restricted riparian protected areas voluntarily assigned by recreational fishing clubs can have positive outcomes for habitat quality and biodiversity, particularly by reducing trampling and access to anglers and other recreationists. Moreover, through provision of key habitat for young fish, small-scale riparian protected areas can also benefit fish abundance and in turn recreational fisheries. • Protection from human access reduces trampling and disturbance by recreationists. • Voluntarily installed protected parts elevate habitat quality in the riparian zone. • Freshwater protected areas maintain sensitive riparian plant and songbird species. • Small riparian protection increases fish abundance relative to areas open to access. • Voluntarily installed protected areas in small lakes have high conservation value. [ABSTRACT FROM AUTHOR]