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Recreational fisheries are valued at $190B globally and constitute the predominant way in which people use wild fish stocks in developed countries, with inland systems contributing the main fraction of recreational fisheries. Although inland recreational fisheries are thought to be highly resilient and self-regulating, the rapid pace of environmental change is increasing the vulnerability of these fisheries to overharvest and collapse. Here we directly evaluate angler harvest relative to the biomass production of individual stocks for a major inland recreational fishery. Using an extensive 28-y dataset of the walleye (Sander vitreus) fisheries in northern Wisconsin, United States, we compare empirical biomass harvest (Y) and calculated production (P) and biomass (B) for 390 lake year combinations. Production overharvest occurs when harvest exceeds production in that year. Biomass and biomass turnover (P/B) declined by ∼30 and ∼20%, respectively, over time, while biomass harvest did not change, causing overharvest to increase. Our analysis revealed that ∼40% of populations were production-overharvested, a rate >10× higher than estimates based on population thresholds often used by fisheries managers. Our study highlights the need to adapt harvest to changes in production due to environmental change.

Species invasions can disrupt aquatic ecosystems by re‐wiring food webs. A trophic cascade triggered by the invasion of the predatory zooplankter spiny water flea (Bythotrephes cederströmii) resulted in increased phytoplankton due to decreased zooplankton grazing. Here, we show that increased phytoplankton biomass led to an increase in lake anoxia. The temporal and spatial extent of anoxia experienced a step change increase coincident with the invasion, and anoxic factor increased by 11 d. Post‐invasion, anoxia established more quickly following spring stratification, driven by an increase in phytoplankton biomass. A shift in spring phytoplankton phenology encompassed both abundance and community composition. Diatoms (Bacillaryophyta) drove the increase in spring phytoplankton biomass, but not all phytoplankton community members increased, shifting the community composition. We infer that increased phytoplankton biomass increased labile organic matter and drove hypolimnetic oxygen consumption. These results demonstrate how a species invasion can shift lake phenology and biogeochemistry. [ABSTRACT FROM AUTHOR]

Predation by native predators can hinder the success of an invasive species. Bythotrephes, an invasive zooplankton species, established in Trout Lake, Vilas County, Wisconsin, USA, in 2014. However, by 2020, Bythotrephes densities dropped to densities where they were barely detectable. Cisco (Coregonus artedi), a native zooplanktivore, is an abundant fish species in Trout Lake and has been shown to significantly prey on Bythotrephes. Given the decline in Bythotrephes, we asked whether Cisco predation could have played a role in the observed decline in Bythotrephes densities. We modeled Cisco consumption of Bythotrephes using bioenergetic modeling and Bythotrephes production from a production to biomass model. The model results suggested that Cisco consumption was lower than Bythotrephes production during the early years of the invasion, but since 2017 Cisco consumption exceeded Bythotrephes production and has likely played a role in the observed Bythotrephes density declines. Our study provides quantitative context for predation on Bythotrephes, and alongside other studies, suggests native predators can control Bythotrephes densities. Leveraging predation by native species could be an invasive species management tool, so it is important to synthesize and document cases in which predation may control or reduce impacts of invasive species. Invasive species can have severe impacts on freshwater ecosystems and will continue to spread across the landscape. When species do invade, invasive species management tools are incredibly important as they can mitigate impacts. However, successful management of invasive species often goes undocumented. Predation by native species can be an invasive species management tool to mitigate impacts of invasions. Leveraging native species to reduce the abundance of an invasive species can be difficult and requires thorough consideration of indirect impacts. There have been some cases where predation by native species has been attributed to controlling the abundances of invasive species. In such cases, promoting native species abundances can reduce the abundance of invasive species. This can be highly advantageous for lake managers, however, natural resource management includes many different stakeholders and therefore decisions regarding invasive species management can be complex. [ABSTRACT FROM AUTHOR]

Predator–prey coupling can result in oscillations of predator–prey densities. These oscillations in predator–prey densities correspond to oscillations in intraspecific competition where a high population density causes high intraspecific competition. Strong coupling of native species can however be disrupted by the introduction of invasive species into food webs. Here, we investigated how the body condition (body mass relative to body length) of a predator, lake trout, and its primary prey, cisco, changed as their respective population densities shifted. We found that the body condition of lake trout and cisco was strongly influenced by their respective population densities, that is, density dependence. The body conditions of lake trout and cisco were also inversely related, which highlights strong predator–prey coupling. Further, we were able to detect the impacts of a recent invasive species, Bythotrephes, as we saw size‐specific shifts in the body condition of prey following the invasion. Overall, this study highlights how the long‐term study of a simple measure, body condition, can reveal predator–prey coupling and yield new insights into the impacts of an invasive species. [ABSTRACT FROM AUTHOR]

Stable isotopes are widely employed to describe energy flow in aquatic communities, though interpretation of results can be confounded by the fact that organisms integrate over vastly different time scales. We used results from a 56-day whole-lake [sup.13]C addition and a bioenergetic modeling approach to estimate dorsal muscle carbon turnover rates in a natural setting for three sizes of bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), and yellow perch (Perca flavescens). Generally, dynamic δ[sup.13]C models with a metabolic tissue replacement term were better supported than models predicting isotopic change from growth alone, except when relative growth rates were highest (age 0 bluegill). Across species and size classes, the percentage of carbon change due to tissue replacement was variable (2%-80%) and independent of fish size. The half-life of δ[sup.13]C in age 0 fishes was similar and ranged from 8 to 18 days. In contrast, adult tissue half-lives were much longer (116-173 days). Based on these and previously published estimates, fish mass (g) was a strong predictor of fish carbon turnover rates, λ: log(λ) = -3.65 - 0.20log(mass), [r.sup.2] = 0.71. Les isotopes stables servent couramment a decrire le flux d'energie dans les communautes aquatiques, meeme si le fait que les divers organismes les integrent a des eechelles temporelles extremement differentes peut introduire de la confusion dans l'interpretation des resultats. Nous utilisons une addition expeerimentale de [sup.13]C de 56 jours dans un lac entier et une meethodologie de modelisation bioenergeetique pour estimer dans un environnement naturel les taux de remplacement du carbone dans le muscle dorsal chez trois tailles de crapets arlequins (Lepomis macrochirus), d'achigans a grande bouche (Micropterus salmoides) et de perchaudes (Perca flavescens). En general, les modeles dynamiques de δ[sup.13]C avec un terme de remplacement meetabolique des tissus fonctionnent mieux que les modeles qui predisent les changements isotopiques a partir de la seule croissance, sauf lorsque les taux de croissance relative sont a leur maximum (les crapets arlequins d'age 0). Le pourcentage de changement de carbone du au remplacement des tissus est variable (2-80 %) et independant de la taille des poissons chez les differentes especes et les classes de taille. La demi-vie de δ[sup.13]C est semblable chez tous les poissons d'age 0 et varie de 8-18 jours. En revanche, les demi-vies dans les tissus adultes sont beaucoup plus longues (116-173 jours). D'apres les presentes estimations et d'autres publieees anterieurement, la masse du poisson (g) est une bonne variable predictive des taux de remplacement du carbone (λ) chez les poissons: log(λ) = -3,65 - 0,20log(masse), [r.sup.2] = 0,71. [Traduit par la Redaction], Introduction The relationship between carbon stable isotopes in fish tissues and their diets has proven a valuable tool for tracing energy flow in food webs (DeNiro and Epstein 1978; Peterson [...]

Stream restoration projects often aim to benefit aquatic biota and frequently use the reappearance of sensitive nongame fish species as a measure of restoration success. However, mitigation of human influence will only benefit a given species where static habitat characteristics are suitable for that species and where potential source populations are within the range of their dispersal capability. We used spatial autoregressive habitat models to simulate the effect of watershed-scale stream restoration on the distributions of six sediment-sensitive fish species in Wisconsin, USA, streams. These models consider the probability of occurrence of a species in a given stream segment as a function of characteristics of that segment as well as the characteristics of neighboring segments. Populations of individual species are predicted to be restorable in 0.2%-2.8% of Wisconsin streams. Streams with high restoration potential for one or more species generally have high watershed human land use but are also closely connected through the stream network to relatively undisturbed streams. These results indicate that habitat restoration for nongame stream fishes will be most effective when it builds onto existing suitable habitat because of both dispersal limitation and spatial autocorrelation of habitat characteristics. Resume: Les projets de restauration des cours d'eau visent souvent a favoriser les organismes aquatiques et utilisent frequemment la reapparition d'especes de poissons non sportifs sensibles comme mesure du succes de la restauration. Cependant, la mitigation de l'influence anthropique ne va beneficier a une espece seulement la ou les caracteristiques statiques de l'habitat sont adequates pour cette espece et lorsque des populations sources potentielles existent dans la portee de leur capacite de dispersion. Nous utilisons des modeles spatiaux autoregressifs de l'habitat pour simuler l'effet d'une restauration a l'echelle du bassin versant sur la repartition de six especes de poissons sensibles aux sediments dans des cours d'eau du Wisconsin, E.-U. Ces modeles tiennent compte de la probabilite de la presence d'une espece dans un segment donne d'un cours d'eau comme une fonction des caracteristiques de ce segment et aussi des caracteristiques des segments voisins. Nous predisons que des populations des differentes especes particulieres peuvent etre restaurees dans 0,2%-2,8% des cours d'eau du Wisconsin. Les cours d'eau qui presentent un fort potentiel de restauration pour une ou plusieurs especes ont generalement une importante utilisation humaine de leur bassin versant, mais ils ont aussi par leur reseau hydrographique des connections proches a des cours d'eau relativement peu perturbes. Nos resultats indiquent que la restauration des habitats pour les poissons lotiques non sportifs sera la plus efficace si elle se base sur un habitat existant adequat, etant donne les limites de la dispersion et l'autocorrelation spatiale des caracteristiques de l'habitat. [Traduit par la Redaction], Introduction A common goal of stream restoration is to benefit aquatic biota, particularly fish. The 'field-of-dreams' hypothesis (Palmer et al. 1997) suggests that if habitat is restored, species of interest [...]