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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]

Positively size-selective vulnerability to fishing is well established in recreational fisheries. Size-selective harvesting can either induce an indirect selection response of behavioural traits that are correlated with size or exert direct selection pressures on behaviours that contribute to vulnerability. In addition, learning to avoid future capture may always happen. Behavioural change caused by fishing may in turn affect the size-selective properties of angling. To test this prediction, field experiments with amago salmon (Oncorhynchus masou ishikawae) were conducted. We demonstrated that, as expected, large fish were more vulnerable than smaller individuals in a low fishing pressure (LP) stream and that positively size-selective angling was not (or no longer) present in a high fishing pressure (HP) stream. Moreover, fish in the HP stream were by far less vulnerable to angling with natural bait than fishes in the LP stream. Laboratory studies showed that offspring from HP streams were intrinsically shyer than offspring collected from LP streams. We propose that the increased timidity of individuals inhibiting HP streams disrupted the generally positive relationship among salmon body size and its vulnerability to angling. Fisheries-induced timidity in response to high exploitation rates reduces catchability, affects the size-selective properties of angling, reduces the value of fishery-dependent stock assessments, and potentially affects trophic interactions. La vulnerabilite a la peche positivement reliee a la taille est un phenomene bien documente dans les peches sportives. La peche avec selection selon la taille peut soit induire une reaction de selection indirecte de caracteres comportementaux qui sont correles a la taille ou exercer des pressions de selection directes sur des comportements qui accroissent la vulnerabilite. En outre, l'apprentissage de l'evitement de captures futures peut toujours se produire. Les changements comportementaux causes par la peche peuvent, quant a eux, avoir une incidence sur les proprietes de selection selon la taille de la peche. Pour verifier cette prediction, des experiences sur le terrain avec des saumons amago (Oncorhynchus masou ishikawae) ont ete menees. Nous avons demontre que, comme prevu, les grands poissons etaient plus vulnerables que les poissons plus petits dans un cours d'eau caracterise par une faible pression de peche (LP) et que la peche avec selection positive selon la taille n'etait pas (ou plus) presente dans un cours d'eau caracterise par une forte pression (HP). De plus, les poissons dans le cours d'eau HP etaient beaucoup moins vulnerables a la peche sportive avec des appats naturels que les poissons dans le cours d'eau LP. Des etudes en laboratoire ont demontre que la progeniture provenant des HP etait intrinsequement plus timide que la progeniture prelevee des cours d'eau LP. Nous proposons que la timidite accrue des individus dans les cours d'eau HP perturbe la relation generalement positive entre la taille du corps des saumons et leur vulnerabilite a la peche sportive. La timidite induite par la peche en reaction a des taux d'exploitation eleves reduit la capturabilite, influence les proprietes de selection selon la taille de la peche, reduit la valeur des evaluations des stocks dependant de la peche et pourrait avoir une incidence sur les interactions trophiques. [Traduit par la Redaction], Introduction Recreational fishing can induce evolutionary changes in life history, morphology, physiology, and behaviour in response to excessive and (or) trait-selective exploitation (e.g., Uusi-Heikkila et al. 2008, 2015; Sutter et [...]

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]

Humanity is facing a biodiversity crisis, with freshwater‐associated biodiversity in a particularly dire state. Novel ecosystems created through human use of mineral resources, such as gravel pit lakes, can provide substitute habitats for the conservation of freshwater and riparian biodiversity. Many of these artificial ecosystems are subject to a high intensity of recreational use, however, which may limit their biodiversity potential.The species richness of several taxa (plants, amphibians, dragonflies, damselflies, waterfowl, and songbirds) was assessed and a range of taxonomic biodiversity metrics were compared between gravel pit lakes managed for recreational fisheries (n = 16) and unmanaged reference lakes (n = 10), controlling for non‐fishing‐related environmental variation.The average species richness of all the taxa examined was similar among lakes in both lake types and no substantial differences in species composition were found when examining the pooled species inventory. Similarly, there were no differences between lake types in the presence of rare species and in the Simpson diversity index across all of the taxa assessed.Variation in species richness among lakes was correlated with woody habitat, lake morphology (surface area and steepness), and land use, but was not correlated with the presence of recreational fisheries. Thus, non‐fishing‐related environmental variables had stronger effects on local species presence than recreational fisheries management or the presence of recreational anglers.Collectively, no evidence was found that anglers and recreational fisheries management constrain the development of aquatic and riparian biodiversity in gravel pit lakes in the study region; however, the conservation of species diversity in gravel pit lakes could benefit from an increasing reliance on habitat enhancement activities. [ABSTRACT FROM AUTHOR]

Human exploitation of wild-living animals has been suggested to create a 'landscape of fear'. A consequence could be that individuals surviving intensive harvesting, either as a result of behavioural plasticity and/or evolutionary change, exhibit increased average timidity. In the aquatic world, such effects are particularly well documented in passively operated fishing gears common to many commercial and recreational fisheries, such as angling, trapping or gill netting. We thus propose that an exploitation-induced timidity syndrome should be a widespread pattern in fisheries. Importantly, we argue that the syndrome can be associated with several ecological and managerial consequences for social groups, populations, food webs, fisheries and assessment of stocks. We suggest research priorities to deepen our understanding of how exploited fish populations behaviourally respond to harvesting. [ABSTRACT FROM AUTHOR]

Competing Interests: The authors declare no conflict of interest.