Search

Invasive species can achieve incredibly high densities in invaded ecosystems, introducing a novel resource base for willing consumers. Hyperabundant invaders in one ecosystem that spillover into adjacent ecosystems (e.g. terrestrial to aquatic) create new opportunities for multichannel omnivory, whereby generalist consumers feed on prey from different trophic levels and ecosystems. However, our understanding of how invasive organisms originating in one ecosystem are utilized by consumers in adjacent ecosystems remains poorly studied. The spongy moth (Lymantria dispar dispar; LDD) is an invasive invertebrate that exhibits cyclical hyperabundance, with larvae defoliating millions of hectares of deciduous forest during regular outbreaks in eastern North America. We sought to determine if larval LDD could represent an impactful spring and early summer resource for native fish species during years of high larval abundance. Here, we quantified the diets of pond-dwelling largemouth bass (Micropterus nigricans) and pumpkinseed sunfish (Lepomis gibbosus) during 2020 and 2021 respectively, two historic outbreak years for LDD in Ontario, Canada. Both pumpkinseed and largemouth bass failed to exhibit meaningful exploitation of LDD larvae, regardless of their overwhelming abundance. Of 315 pumpkinseed sampled across four pond populations from April to August of 2021, only two contained individual LDD larvae. Of the 82 largemouth bass sampled in June 2020, only 1 individual contained a single LDD larvae. Serendipitously, we discovered one pumpkinseed population relied heavily on a different invasive terrestrial invertebrate, the earthworm (60% of all pumpkinseed stomach contents by mass in early spring). Though hyperabundant LDD larvae appeared to be largely avoided by fish predators, a less well-defended invasive invertebrate (earthworms) acted as a terrestrial subsidy for a native fish. Despite LDD larvae not being consumed by fish, the replacement of leaf litter with the carcasses and frass of LDD larvae could represent an important modification to detrital food webs in ponds and lakes. Thus, understanding how invasive species impact both resident consumers and nutrient cycling will be critical for the appropriate management of invasive species and their resident food webs moving forward.

Natural resource decision makers are challenged to adapt management to a changing climate while balancing short-term management goals with long-term changes in aquatic systems. Adaptation will require developing resilient ecosystems and resilient management systems. Decision makers already have tools to develop or ensure resilient aquatic systems and fisheries such as managing harvest and riparian zones. Because fisheries management often interacts with multiple stakeholders, adaptation strategies involving fisheries managers and other partners focused on land use, policy, and human systems, coupled with long-term monitoring, are necessary for resilient systems. We show how agencies and organizations are adapting to a changing climate in Minnesota and Ontario lakes and Montana streams. We also present how the Florida Fish and Wildlife Commission created a management structure to develop adaptation strategies. These examples demonstrate how organizations and agencies can cope with climate change effects on fishes and fisheries through creating resilient management and ecological systems.

Natural resource decision makers are challenged to adapt management to a changing climate while balancing short-term management goals with long-term changes in aquatic systems. Adaptation will require developing resilient ecosystems and resilient management systems. Decision makers already have tools to develop or ensure resilient aquatic systems and fisheries such as managing harvest and riparian zones. Because fisheries management often interacts with multiple stakeholders, adaptation strategies involving fisheries managers and other partners focused on land use, policy, and human systems, coupled with long-term monitoring, are necessary for resilient systems. We show how agencies and organizations are adapting to a changing climate in Minnesota and Ontario lakes and Montana streams. We also present how the Florida Fish and Wildlife Commission created a management structure to develop adaptation strategies. These examples demonstrate how organizations and agencies can cope with climate change effects on fishes and fisheries through creating resilient management and ecological systems. Los tomadores de decisiones en materia de recursos naturales tienen la tarea de adaptar el manejo a un clima cambiante, y al mismo tiempo sopesar entre los objetivos de corto plazo y los cambios de largo plazo en ecosistemas acuáticos. Esta adaptación requerirá desarrollar tanto ecosistemas como sistemas de manejo resilientes. Los tomadores de decisiones ya cuentan con herramientas para desarrollar o asegurar sistemas acuáticos y pesquerías resilientes, tales como manejo por cuotas y por zonas riparias. En virtud de que el manejo de pesquerías a menudo implica la interacción entre varias partes interesadas, las estrategias de adaptación que involucran a manejadores de pesquerías y otros participantes con intereses en el uso de la tierra, en la política y en sistemas humanos, en conjunto con un monitoreo de largo plazo, son elementos indispensables para constituir sistemas resilientes. Se muestra cómo organizaciones y agencias de los lagos de Minnesota y Ontario y en los ríos de Montana, ya se están adaptando a un clima cambiante. También se muestra cómo la Comisión de Pesca y Vida Silvestre de Florida creó una estructura de manejo con el objeto de desarrollar estrategias de adaptación. Estos ejemplos demuestran cómo las organizaciones y agencias pueden responder a los efectos del cambio climático en materia de peces y pesquerías, a través de la creación de sistemas ecológicos y de manejo resilientes. Les décideurs des ressources naturelles sont mis au défi d'adapter sa gestion aux changements climatiques tout en équilibrant les objectifs de gestion à court terme avec des changements à long terme dans les systèmes aquatiques. L'adaptation exigera de développer la résilience des écosystèmes et de créer des systèmes de gestion souples. Les décideurs disposent déjà d'outils pour développer ou assurer la résilience des systèmes aquatiques et de pêche, tels que la gestion des prises et des zones lacustres. Parce que la gestion de la pêche interagit souvent avec de multiples parties prenantes, des stratégies d'adaptation impliquant les gestionnaires des pêches et d'autres partenaires, qui se concentrent sur l'utilisation des terres, les politiques et les systèmes humains, associés à la surveillance à long terme, sont nécessaires pour les systèmes souples. Nous montrons comment les agences et les organisations s'adaptent aux changements climatiques dans les lacs du Minnesota et de l'Ontario, ainsi qu'au niveau des ruisseaux du Montana. Nous présentons également la façon dont la Commission des poissons et de la faune de la Floride a créé une structure de gestion pour élaborer des stratégies d'adaptation. Ces exemples montrent comment les organisations et les agences peuvent faire face aux effets des changements climatiques sur les poissons et la pêche en créant une gestion et des systèmes écologiques souples.

The ability of coldwater species and populations to respond to the predicted temperature increases associated with climate change will largely depend on existing adaptive potential within and among populations. Southern inland populations of Lake Trout Salvelinus namaycushare broadly characterized by two ecotypes (small and large bodied) which differ in their trophic ecology, life history traits, and body size. Using common-garden experiments, we investigated population-specific differences in thermal performance (growth, temperature tolerance, and temperature preference) and whether the differences were consistent between ecotypes. We further explored the role of acclimation temperature on growth and thermal performance in two representative ecotypic populations. The evidence from this study indicated that the differences were population specific rather than ecotype specific. A strong inverse relationship between early growth rate and temperature preference suggests that the differences in early growth among Lake Trout populations are driven by adaptive variation in temperature preference. Acclimation temperature had a greater effect than source population on growth and temperature tolerance, although both significantly influenced temperature preferences. Small-bodied ecotypes were less tolerant of elevated temperatures and exhibited less within-population variation, potentially indicating their greater vulnerability to changing ecological conditions under climate change scenarios.

Hatcheries play a key role in augmenting populations for conservation, harvest, or both, although rapid domestication and adaptation to hatchery conditions may lead to fish that are maladapted to natural environments. Three processes may lead to domestication: (1) negative selection against fish adapted to wild environments, (2) positive selection for fish that thrive in artificial conditions, or (3) relaxation of selection pressures. In this study, early life history traits and survival were contrasted among wild- and hatchery-origin lake trout Salvelinus namaycushreared in a common hatchery environment to address the hypotheses of processes leading to domestication. Examination of egg size, egg survival, fry deformity, and early growth rate found no evidence of negative selection against wild-origin lake trout or positive selection for hatchery-origin lake trout when reared in a hatchery environment. Wild-origin lake trout outperformed hatchery-origin fish in all life history traits examined, suggesting that relaxation of natural selective pressures may be occurring in the hatchery environment. Furthermore, the hatchery-origin strains failed to show maternal effects on egg size and exhibited limited variability in egg size and hatching time, as well as no significant differences in early growth rate, suggesting potential homogenization of life history traits as a result of the hatchery environment.

Lake trout Salvelinus namaycushexhibit substantial life history variation associated with variation in climatic and biotic variables. To assess the environmental and genetic influences on lake trout life history traits, eggs were collected from two lakes in Algonquin Park, Ontario, Lake Opeongo and Louisa Lake, with contrasting ecotypes and forage bases. Eggs from both populations and interpopulation hybrids (Lake Opeongo females × Louisa Lake males) were raised to maturity in a common controlled environment. There was evidence of a genetic basis to life history variation between ecotypes. Hatchery-reared lake trout from Louisa Lake were found to have a faster prematuration growth rate and earlier age and smaller size at maturation than Lake Opeongo lake trout, whereas Lake Opeongo lake trout had greater postmaturation growth rates. Most of the life history traits of hybrids were intermediate between those of the parent populations. These differences were also consistent with reported differences on these populations in the field. Despite differences in maturation and body size, reproductive investment did not differ significantly among the hatchery-reared populations. There was also evidence of phenotypic plasticity in growth (juvenile and adult) and age at maturity. For fish originating from each lake, hatchery-raised fish showed higher prematuration growth rates and younger ages at maturity than did wild fish. Hatchery-reared fish from Louisa Lake were projected to attain asymptotic sizes nearly 50% larger than those of their wild counterparts. These data provide evidence that wild lake trout populations exhibit a plastic response to resource limitation. The combined results of this study indicate that lake trout life history characteristics are driven by both genetic and environmental influences, which should be incorporated into current life history models and used in making management decisions.

We use an individual-based eco-genetic model to examine the demographic and evolutionary consequences of selective mortality on a species with parental care, the smallmouth bass Micropterus dolomieu. Our analyses are grounded in a long-term (1936-2003) empirical study of the dynamics of two populations that differ widely in both density and life history. The model we construct extends previous approaches by including phenotypic plasticity in age and size at maturation, by permitting density-dependent somatic growth, and by analyzing how costs associated with parental care alter model predictions. We show that, first, additional mortality on age-0 individuals applied for 100 years causes reduced population abundance and biomass, faster somatic growth rates, and phenotypic plasticity toward slightly larger sizes at maturation. Second, mortality on individuals above a minimum size limit, also applied for 100 years, has a small influence on population abundance and somatic growth, causes a reduction of biomass, and substantial evolution of the probabilistic maturation reaction norm, leading to younger ages and smaller sizes at maturation. Third, the incorporation of body-size-dependent survival costs associated with parental care (i.e., by reducing the number of small breeding adults at high population densities, increasing the mortality of parents that breed at small body sizes, or increasing the mortality of offspring originating from small-sized parents) reduces the amount of evolution predicted to occur within 100 years. Together, these results underscore that selective harvest can cause both phenotypically plastic responses and rapid evolution; however, the rate and magnitude of the evolved changes are sensitive to a species' life history characteristics.

Our objective was to assess the dynamics of piscivory by lake trout Salvelinus namaycushin Lake Opeongo, Ontario, following the introduction of smallmouth bass Micropterus dolomieuearly in the 1900s. The effects of this introduction on lake trout were thought to be of slight significance at the time, but they may have been obscured by the introduction of cisco Coregonus artediin 1948. Our analyses of lake trout stomach contents and stable isotopes of archived scales indicated that several dietary changes occurred in advance of the cisco introduction. These changes included the consumption of fewer yellow perch Perca flavescens, fewer but larger lake whitefish C. clupeaformis, and larger lake whitefish for a given lake trout size. Stable isotope analyses were consistent with a decline in the importance of littoral prey for young lake trout before the introduction of cisco. We hypothesize that the indirect effects of smallmouth bass on the pelagic fish community explain these patterns.

We characterized the association between climate and somatic growth in 125 North American populations of smallmouth bass Micropterus dolomieu. Using multivariate techniques (i.e., principal components and Procrustes analyses), we found an overall significant concordance between eight climate variables (cloud cover, frost frequency, precipitation, mean air temperature, minimum air temperature, maximum air temperature, mean summer air temperature, and growing degree-days above 10°C) and four growth variables (body length increments for ages 1–4). Bivariate linear regressions revealed that there was a significant positive relationship between air temperature variables and early growth, while growth at later ages was generally less influenced by climate. Given that the geographical range of smallmouth bass has been rapidly expanding over the past century, we also examined how the climate–growth relationships differed in populations that have been introduced outside the native distribution. Analysis of residuals from the Procrustes test indicated that the concordance between climate and growth was probably higher for populations within the native range and lower for introduced populations. Mechanisms that might generate this pattern include the possibilities that (1) the introduced populations have not had time to adapt to their new environments and (2) growth might respond atypically to the more extreme climates experienced outside the native range of the species.

Fishing for recreation is a popular activity in many parts of the world and this activity has led to the development of a sector of substantial social and economic value worldwide. The maintenance of this sector depends on the ability of aquatic ecosystems to provide fishery harvest. We are currently witnessing the collapse of many commercial marine fisheries due to over-exploitation. Recreational fisheries are typically viewed as different from commercial fisheries in that they are self-sustaining and not controlled by the social and economic forces of the open market that have driven many commercial fisheries to collapse. Here we reject the view that recreational and commercial fisheries are inherently different and demonstrate several mechanisms that can lead to the collapse of recreational fisheries. Data from four high profile Canadian recreational fisheries show dramatic declines over the last several decades yet these declines have gone largely unnoticed by fishery scientists, managers, and the public. Empirical evidence demonstrates that the predatory behavior of anglers reduces angling quality to levels proportional to distance from population centers. In addition, the behavior of many fish species and the anglers who pursue them, the common management responses to depleted populations, and the ecological responses of disrupted food webs all lead to potential instability in this predator-prey interaction. To prevent widespread collapse of recreational fisheries, fishery scientists and managers must recognize the impact of these processes of collapse and incorporate them into strategies and models of sustainable harvest.

We displaced a subset of adult smallmouth bass Micropterus dolomieuimplanted with sonic tags to determine if they returned to home ranges held before their displacement. We also compared their home range characteristics and seasonal movements with those of undisturbed smallmouth bass. Fifteen of the 18 displaced fish returned to the home ranges they held before removal. One fish died soon after release, and two fish remained in the area of release. Displaced smallmouth bass remained at the release site for an average of 1 week (range, 0.5–30 d) and returned to their home ranges in approximately 4 d (range, 1–9 d). On average, displaced fish were away from their home ranges for 11 d. Displaced and control smallmouth bass did not significantly differ with respect to home range area, percent overlap between early and late summer shifts in home ranges, or day of the year when fish left their home ranges for overwintering sites. These results indicate that smallmouth bass displaced by tournament anglers will return to their home ranges after spending approximately 1 week at the release site and will use their home range in a manner similar to that of undisturbed fish.

We examined changes in annual age-specific growth rates of 0–8-year-old lake trout Salvelinus namaycushin Lake Opeongo, Ontario, after the introduction of cisco Coregonus artediiinto the lake in 1948. Growth rates of piscivorous lake trout (ages 3–8) initially increased as the occurrence of ciscoes increased, and then decreased as the abundance of piscivorous lake trout increased and the size of ciscoes eaten decreased. Growth of non-piscivorous 1- and 2-year-old lake trout decreased as the occurrence of insects decreased and the abundance of 1- and 2-yearold fake trout increased. Prey abundance, prey size, and intraspecific competition appeared to be major factors influencing growth rates. As ciscoes came to dominate the diet of adult lake trout, cannibalism by adults on younger lake trout decreased, as did the mortality suffered by young lake trout. The cisco introduction improved the existing sport fishery for lake trout by raising annual maximum sustainable yield from about 0.18 kg/hectare to about 0.48 kg/hectare; however, this increase was accompanied by heightened sensitivity of the population to over exploitation.

We used an individual-based model of dynamics of smallmouth bass Micropterus dolomieuto examine the effect of angling for nesting males on the abundance of age-0 smallmouth bass. Variation in the daily probability of capture, opening date of angling, and probability of a male successfully returning to guard his brood, as well as a contrast between catch-and-keep versus catch-and-release policies were examined. Male body size and the preference of anglers for fish of different size were varied as a demonstration of the complex interactions between the variability in the reproductive ecology of a fish, angler preference, and a fixed management regulation. We found that the abundance of age-0 smallmouth bass decreased as the daily probability of capturing a nesting male increased in both catch-and-keep and catch-and-release policies. Opening dates during the nesting season, when males were guarding broods, also decreased the abundance of age-0 fish. This decrease was dramatic when the opening date occurred early in the parental care period relative to late in the period. Stress resulting from handling time for catch-and-release can have a significant impact on the abundance of age-0 fish because nesting males may abandon guarding behavior. The simulations indicate that closed fishing seasons during the parental care period, particularly during the early stages of parental care, may be a viable management option in areas where anglers target nesting males.

We link life history theory, environmental setting, and individual-based modeling to compare the responses of two fish species to environmental change, Life history theory provides the framework for selecting representative species, and in combination with information on important environmental characteristics, it provides the framework for predicting the results of model simulations. Individual-based modeling offers a promising tool for integrating and extrapolating our mechanistic understanding of reproduction, growth, and mortality at the individual level to population-level responses such as size-frequency distributions and indices of year-class strength. Based on the trade-offs between life history characteristics of striped bass Morone saxatilisand smallmouth bass Micropterus dolomieuand differences in their respective environments, we predicted that young-of-year smallmouth bass are likely to demonstrate a greater compensatory change in growth and mortality than young-of-year striped bass in response to changes in density of early life stages and turnover rates of zooplankton prey. We tested this prediction with a simulation experiment. The pattern of model results was consistent with our expectations: By the end of the first growing season, compensatory changes in length and abundance of juveniles were more pronounced for smallmouth bass than for striped bass. The results also highlighted the dependence of model predictions on the interplay between density of larvae and juveniles and characteristics of their zooplankton prey.

We investigated effects of starvation on acid tolerance of young-of-year smallmouth bass Micropterus dolomieuiin the laboratory. Juvenile smallmouth bass, held under simulated winter conditions for up to 5 months, experienced losses in ash-free dry weight of up to 30%. However, consecutive tests failed to demonstrate any decline in the short-term (=7 d) tolerance of these fish for pH levels in the range from 3.0 to 4.5. We discuss the implications of these findings for northern populations where young-of-year fish experience significant winter starvation, followed by short-term exposure to low pH in spring. Calcium and sodium concentration of the water and fish body size (fork length) were all positively related to acid tolerance. A doubling of fork length increased survival time at any pH by 100%. At pH 3.0, a doubling of calcium concentration increased survival time by 13% and at pH 4.0 it increased survival time by 50%. Over the pH range 3.75 to 4.0, a doubling of sodium concentration increased survival time by 8%. The strong effect offish body size on acid tolerance should be recognized and controlled in future acid tolerance experiments. It should be taken into account when laboratory tolerance estimates are used to assess the susceptibility of wild populations to acid stress.

We used daily air and water temperatures from 14 lakes in Ontario to develop and test a simple method for constructing lake-specific empirical models for predicting daily littoral water temperatures. Data requirements for prediction are modest (average air temperature, day of the year) and the method is robust and practical, requiring only a few (15–20) well-spaced water temperature observations to construct a single-year model that can generate reasonably accurate predictions for an entire ice-free season. The ability of a singe-lake model to predict several years of temperature data is significantly improved by explicitly including information on ice-out date in the model. Our multiyear model for Lake Opeongo described most (18 of 22) years well. Years that were not well described were usually coincident with El Nino Southern Oscillation events. Used with caution, the method can be an effective tool for supplementing direct monitoring of littoral water temperatures and for generating historical water temperature estimates when direct estimates are lacking. These capabilities should be of particular use to fisheries biologists studying or managing populations of fish species with critical life stages that are affected by littoral water temperatures.