Michael J. Weber

Effects of Common Carp on Aquatic Ecosystems 80 Years after “Carp as a Dominant”: Ecological Insights for Fisheries Management

The introduction of fishes into habitats outside their native range may result in dramatic ecosystem alterations. Circumpolar introductions of common carp Cyprinus carpio commonly induce perturbations to shallow lakes, inducing a phase shift from clear to turbid water. Cahn (1929) first reported a phase shift following common carp introduction. Since then, ecologists have sought to understand ecosystem responses to common carp perturbation. We present a synthesis on how common carp can affect aquatic ecosystems through a middle-out framework due to their capability to alter bottom-up and top-down processes. Common carp affect bottom-up processes by modifying nutrient and turbidity concentrations and phytoplankton abundance and diversity through benthic foraging, whereas zooplankton and benthic invertebrates can be affected by top-down processes through predation and reduced foraging efficiency. Common carp also reduce aquatic macrophytes that may switch lakes from the clear to turbid water equilibrium. Restoration efforts seeking to return ecosystems to the clear water state have attempted to remove common carp populations through numerous methods with varying success. Restoration efforts should focus on entire ecosystems (humans, habitats, and biota) in conjunction with common carp reductions to achieve the greatest success at minimizing the effects of common carp and to return lakes to the clear water state.

Simulated Population Responses of Common Carp to Commercial Exploitation

Abstract Common carp Cyprinus carpio is a widespread invasive species that can become highly abundant and have deleterious ecosystem effects. Thus, aquatic resource managers are interested in controlling common carp populations, but control is difficult, in part, because of the inherent uncertainty as to how populations respond to exploitation. To better understand this response, we evaluated the population dynamics (recruitment, growth, and mortality) of common carp in three natural lakes in eastern South Dakota. Common carp exhibited similar population dynamics across these three systems, which were characterized by consistent recruitment (ages 3–15 being present), fast growth (K = 0.37–0.59), and low mortality (A = 1–7%). We then modeled the effects of commercial exploitation on size structure, abundance, and egg production to determine its utility as a management tool to control populations. All three populations responded similarly to exploitation simulations in which a 575-mm length restriction repr...

Old Tales in Recent Context: Current Perspective on Yellow Perch Recruitment in Lake Michigan

Abstract To evaluate factors affecting recruitment of yellow perch Perca flavescens in southwestern Lake Michigan, a Ricker stock–recruitment model was fitted to age-0 abundance estimated from a fall bottom trawl survey (1989–2007) and spawning stock biomass estimates. Models were built for all possible combinations of four external variables: spring–summer water temperature, June nearshore zooplankton density, spring abundance of alewives Alosa pseudoharengus, and an index of wind-induced transport of yellow perch larvae. Four relatively parsimonious models were deemed robust, and three external variables were represented (spring–summer water temperature, spring alewife abundance, and June zooplankton density). The Ricker stock–recruitment model with the lowest value of Akaikes information criterion (i.e., the best-supported model) included spring–summer water temperature and spring alewife abundance. The basic Ricker stock–recruitment model ranked second, followed by the Ricker model that included June...

Growth and Survival of Age-0 Yellow Perch across Habitats in Southwestern Lake Michigan: Early Life History in a Large Freshwater Environment

Abstract Processes regulating the survival of early life stages are difficult to decipher for fishes, especially those occupying multiple spatially segregated habitats in large complex systems. Although the processes occurring during the juvenile period are often thought to regulate recruitment of freshwater fishes, those occurring during prolonged pelagic larval phases may be more important to fishes inhabiting large dynamic systems, as is the case with marine larvae. To assess the importance of biotic and abiotic factors on growth and survival of a freshwater fish with a prolonged larval phase, we collected age-0 yellow perch Perca flavescens in Lake Michigan across multiple habitats and used otoliths to estimate daily ages, hatching distributions, and growth and mortality rates. Larval yellow perch hatched near shore over a 4- to 6-week period but were quickly transported offshore, where they experienced prolonged pelagic durations. Water temperature and wind events influenced growth rates, whereas wat...

Metabolic theory explains latitudinal variation in common carp populations and predicts responses to climate change

Climate change is expected to alter temperature regimes experienced by fishes, which may also alter life history traits. However, predicting population-level responses to climate change has been difficult. Metabolic theory of ecology has been developed to explain how metabolism controls a variety of ecological processes, including life history attributes. Thus, this theory may be a useful tool for predicting fish population responses to climate change. To understand how climate change may alter freshwater fish life history, we measured population characteristics (e.g., recruitment, growth, body size, and mortality) of 21 North American common carp Cyprinus carpio populations spanning a latitudinal gradient of >2,700 km. We then evaluated (1) how metabolic rates vary with body size and temperature (i.e., metabolic theory of ecology) to interpret latitudinal patterns in life history traits and (2) how predicted increases in annual temperature as a result of climate change may alter metabolism and population...

Continuous, pulsed and disrupted nutrient subsidy effects on ecosystem productivity, stability, and energy flow

Resource pulses and subsidies can supply ecosystems with an important source of nutrients that supports additional productivity at multiple trophic levels. Common carp Cyprinus carpio provide ecosystems with a continuous nutrient subsidy through bioturbation and excretion but may also initiate a nutrient pulse through carcass decomposition. We examined how continuous (common carp foraging and excretion), pulsed (carcass decomposition) and disrupted (carp introduced and then removed) nutrient subsidies differed in their ability to alter nutrient availability, ecosystem productivity and stability and energy flow. Nitrogen and phosphorus availability and primary production were highest in pulsed, intermediate in continuous and lowest for disrupted and control systems. Continuous, and to a lesser extent pulsed, systems were associated with decreased water clarity and macrophyte coverage. Nutrient pulses ascended to higher trophic levels and supported greater densities of consumers (i.e., zooplankton and macroinvertebrates). Biotic and abiotic responses in disrupted systems quickly returned to control levels and water quality improved. Light penetration and Daphnia spp. dynamics were more stable in systems with pulses whereas stability of other variables was similar across treatments. Biotic materials collected from pulsed and continuous subsidy systems were typically enriched in δ15N suggesting common carp-derived nutrients supported increased productivity whereas δ13C signatures were depleted suggesting a transition to more pelagic energy pathways, likely due to enhanced phytoplankton production. Our results suggest that continuous and pulsed nutrient subsidies vary in their ability to support and sustain ecosystem productivity with resulting variation in food web structure and ecosystem stability.

Effect of Passive Integrated Transponder Tag Implantation Site on Tag Retention, Growth, and Survival of Two Sizes of Juvenile Bluegills and Yellow Perch

Abstract Passive integrated transponder (PIT) tags are commonly used to monitor growth, habitat use, activity rates, and survival of individual fish. However, for successful completion of research objectives, the tags must be retained and must not affect fish growth or survival. We compared the effects of PIT tagging location on tag retention, growth, and survival of juvenile bluegills Lepomis macrochirus and yellow perch Perca flavescens. In total, 80 bluegills and 80 yellow perch from two size-classes (75–101 and 128–162 mm total length) were randomly assigned to a control or to one of three tagging location treatments: isthmus, body cavity, or dorsal musculature. Fish received daily ad libitum rations and were monitored for survival. On days 14, 28, and 42, the fish were measured, weighed, and checked for tag retention. Use of the isthmus as a tagging location resulted in lower tag retention for both species and both size-classes relative to the body cavity and dorsal musculature locations. Tagging loc...

Density-Dependence and Environmental Conditions Regulate Recruitment and First-Year Growth of Common Carp in Shallow Lakes

Abstract Recruitment dynamics of fishes can determine their abundance and subsequent effects of adult populations on ecosystem properties. Common Carp Cyprinus carpio is a widespread invasive species that can exert negative density-dependent effects on aquatic food webs. However, little is known concerning processes that regulate their recruitment. We used summer-through-fall electrofishing catch rates of age-0 Common Carp to investigate the importance of biotic (stock size, prey availability, egg and juvenile predation, intraspecific competition) and abiotic (water level fluctuation, temperature, wind events) factors on recruitment and growth in 13 lakes across eastern South Dakota from 2008 to 2010. Mean relative abundance of age-0 Common Carp was highly variable spatially and temporally, ranging from 0 to 152.2 fish per hour of electrofishing. Ricker stock–recruitment models indicated that peak production of age-0 Common Carp occurred when adult Common Carp relative abundance was low. Recruitment also ...

Effects of Predator–Prey Interactions and Benthic Habitat Complexity on Selectivity of a Foraging Generalist

Abstract Predators typically prefer specific prey types but include others in their diet as a result of opportunistic foraging, prey availability, or foraging costs. Habitat complexity may interact with preferences by altering prey availability and foraging strategies, affecting the preferences and consumption patterns of predators. Yellow perch Perca flavescens is perceived as a foraging generalist and the predominant predator in numerous systems. In the laboratory, we compared the prey selection of yellow perch (230–311 mm) foraging on common Great Lakes prey species—northern crayfish Orconectes virilis, round gobies Neogobius melanostomus, and alewives Alosa pseudoharengus—in simple and complex benthic habitats. Yellow perch selected alewives in both simple and complex habitats. Removal of the preferred prey species resulted in neutral selection for both of the remaining prey species in simple benthic habitat but selection for round gobies and against crayfish in complex habitat. Predator behaviors ind...

Laboratory Evaluation of a Bioacoustic Bubble Strobe Light Barrier for Reducing Walleye Escapement

AbstractFish escapement is a largely overlooked challenge to managing reservoir fisheries. Physical barriers may help retain fish in reservoirs but are often not practical due to high reservoir debris loads and maintenance requirements of these structures. As an alternative, nonphysical barriers may also be successful at increasing fish retention in reservoirs through the use of negative stimuli that divert fish away from targeted locations. However, the effectiveness of nonphysical barriers can vary considerably among barrier stimuli and fish species because the barriers success is dependent upon on a behavioral response from fish. We conducted a laboratory experiment to evaluate the effectiveness of a bioacoustic bubble–strobe light barrier at reducing Walleye Sander vitreus escapement rates. We hypothesized that increasing the number and frequency of barrier stimuli would result in Walleyes approaching the barrier less frequently, reduced escapement, and increased amount of time before escapement occu...