Przemyslaw G. Bajer

Recruitment and abundance of an invasive fish, the common carp, is driven by its propensity to invade and reproduce in basins that experience winter-time hypoxia in interconnected lakes

Although the common carp is globally distributed, it only reaches extreme densities in certain regions. We hypothesized that this phenomenon might be linked to recruitment bottlenecks which carp overcome where environmental conditions create unstable peripheral areas that it can access for spawning and nursery habitat. To test this hypothesis, the abundance, movement and reproductive success of carp was determined in two systems of inter-connected lakes in the North American Midwest whose shallow basins frequently experience winter-hypoxia (‘winterkill’). Radio-tracking demonstrated that while adult carp overwinter in deep lakes that do not winterkill, they aggressively move into winterkill-prone shallow regions in the spring to spawn. The significance of this behavior was demonstrated by ageing analyses which found that carp recruit only in interconnected shallow lakes and then only in years following severe winter hypoxia. Presumably this strategy allows carp to exploit nursery habitat that is relatively free of predators. It likely evolved in response to seasonally variable conditions in the carp’s native habitat in the Ponto-Caspian region. This life history may also explain the carp’s abundance in other unstable regions such as southern Australia and could potentially be exploited to control this damaging invasive.

The Relationship between the Distribution of Common Carp and Their Environmental DNA in a Small Lake

Although environmental DNA (eDNA) has been used to infer the presence of rare aquatic species, many facets of this technique remain unresolved. In particular, the relationship between eDNA and fish distribution is not known. We examined the relationship between the distribution of fish and their eDNA (detection rate and concentration) in a lake. A quantitative PCR (qPCR) assay for a region within the cytochrome b gene of the common carp (Cyprinus carpio or ‘carp’), an ubiquitous invasive fish, was developed and used to measure eDNA in Lake Staring (MN, USA), in which both the density of carp and their distribution have been closely monitored for several years. Surface water, sub-surface water, and sediment were sampled from 22 locations in the lake, including areas frequently used by carp. In water, areas of high carp use had a higher rate of detection and concentration of eDNA, but there was no effect of fish use on sediment eDNA. The detection rate and concentration of eDNA in surface and sub-surface water were not significantly different (p≥0.5), indicating that eDNA did not accumulate in surface water. The detection rate followed the trend: high-use water > low-use water > sediment. The concentration of eDNA in sediment samples that were above the limit of detection were several orders of magnitude greater than water on a per mass basis, but a poor limit of detection led to low detection rates. The patchy distribution of eDNA in the water of our study lake suggests that the mechanisms that remove eDNA from the water column, such as decay and sedimentation, are rapid. Taken together, these results indicate that effective eDNA sampling methods should be informed by fish distribution, as eDNA concentration was shown to vary dramatically between samples taken less than 100 m apart.

Variation in native micro-predator abundance explains recruitment of a mobile invasive fish, the common carp, in a naturally unstable environment

Why certain species of fish become invasive is poorly understood and a key obstacle to restoring many of the world’s ecosystems. In this study we tested whether variation in biotic resistance exerted by native predators might explain the reproductive success of the common carp, a large and fecund invasive species that typically spawns in outlying and unstable shallow habitat. An initial three-year study of the relative abundance of young-of-year (YOY) carp in interconnected lakes in the Upper Mississippi River Basin discovered that YOY carp are only found in shallow waters that experience winter hypoxia (winterkill) and have low densities of the native egg-predators that otherwise dominate these locales. A follow-up experiment tested if native fish predation on carp eggs could explain this distribution. It found that while carp eggs survived in winterkill lakes, they only survived in non-winterkill lakes when protected by a mesh that excluded fish. Large numbers of carp eggs were found in the stomachs of native fish inhabiting lakes that did not winterkill. We conclude that common carp, and likely many other highly mobile and fecund invasive fish, have evolved life histories to avoid egg predators and can become invasive when they are absent.

Using Boat Electrofishing to Estimate the Abundance of Invasive Common Carp in Small Midwestern Lakes

Abstract The common carp Cyprinus carpio is among the most invasive fish worldwide, but practical methods for estimating its abundance have not yet been developed. Particularly needed are methods that can accurately assess low densities of common carp to enact proactive management strategies before populations reach damaging levels. In this study we tested whether the density of adult common carp in small Minnesota lakes could be accurately predicted from their catch rates using boat electrofishing. We used mark and recapture to estimate the abundance of common carp in eight Midwestern lakes with a wide range of common carp densities (13–400 carp/ha), while also surveying each lake using boat electrofishing. In addition, we reduced common carp abundance by up to 90% in two lakes to test whether this was accompanied by a similar drop in electrofishing catch rates. A regression analysis showed that electrofishing catch rates increased linearly with increasing densities of common carp. A cross-validation pro...

Use of Erythrocyte Measurements to Identify Triploid Saugeyes

Abstract The use of erythrocyte size measurements as a possible alternative to flow cytometry for identifying triploid saugeyes (female walleye Stizostedion vitreum × male sauger S. canadense) was evaluated. Blood smear preparations were made from 32 heat-shocked saugeyes (1.0-42.7 g; 52-185 mm total length), which consisted of 12 diploids and 20 triploids, as determined by flow cytometry after blood cells were stained with propidium iodide. The length, width, surface area, and volume of the cell and nucleus of 100 erythrocytes were determined for each fish. The cell and nuclear dimensions were measured at 1,000× magnification with a calibrated ocular micrometer. Discriminant analysis was used to distinguish diploids and triploids based on their score profiles. Results showed that triploid saugeyes had significantly larger erythrocyte cell and nucleus measurements than their diploid counterparts (N = 32; P < 0.0001). Erythrocyte measurements correctly distinguished 93.8% of fish samples as diploids or tri...

Improvement of Bioenergetics Model Predictions for Fish Undergoing Compensatory Growth

Abstract A previous evaluation of a bioenergetics model applied to juvenile hybrid sunfish (F1 hybrid of female green sunfish Lepomis cyanellus × male bluegill L. macrochirus) undergoing compensatory growth (CG) indicated that the model substantially overestimated growth and underestimated cumulative consumption. This result suggested that fish bioenergetics models might not adequately account for physiological shifts that occur during CG. However, we demonstrate that application of a recently developed procedure for correcting consumption- and growth-rate-dependent systematic errors common among bioenergetics models negates much of the predictive error that had been attributed to the physiological complexities of CG. Correction equations for estimating the model-relative growth rate error (predicted less observed; g · g−1 · d−1) from the observed mean daily consumption rate (g · g−1 · d−1) and the consumption rate error (predicted less observed; g · g−1 · d−1) from the observed relative growth rate (g · ...

Intensive Culture of Walleye Larvae Produced Out of Season and during Regular Season Spawning

Abstract The performance of larval walleyes Stizostedion vitreum that were produced out of season was compared with larvae produced during a regular season, using intensive culture methods. Wild-captured walleye adults were held in an earthen pond beginning in late November and then gradually transferred to higher water temperatures before ovulation was hormonally induced in February. A second batch of walleye larvae was obtained from a hatchery operation in April and otherwise reared in similar conditions. The two experiments were conducted to evaluate survival and growth of walleye larvae reared initially on live nauplii of brine shrimp Artemia salina and then gradually weaned to commercial diets. Larvae were stocked at 20 fish/L and raised in large (800-L) triplicate tanks provided with turbid water (40–50 nephelometric turbidity units) and surface sprays. Mean final weight of fish after 32 d of rearing from the first (February; 100.5 ± 17.5 mg) and second (April; 111.2 ± 18.0 mg) batch did not differ ...

Laboratory Evaluation of Two Bioenergetics Models for Brown Trout

Abstract Laboratory growth and food consumption data for two size-classes of brown trout Salmo trutta subjected to three distinct feeding regimes at two temperatures were used to evaluate the ability of two bioenergetics models to predict fish growth. Accuracy of cumulative consumption predictions was also tested for one of the models. Consumption-dependent prediction error has been commonly observed in bioenergetics models for other fish species; model errors for predicting relative growth rate of individual fish were regressed on observed mean daily consumption rate to assess whether the two bioenergetics models exhibited this type of error. Both models yielded unbiased estimates of brown trout growth that were within 1–12% of observed values across the range of fish sizes, water temperatures, and ration levels tested. For regressions of predicted versus observed final weight, the Bonferroni joint 95% confidence intervals for slope included 1 and confidence intervals for the y-intercept included 0 for b...

Local-Search Strategy for Active Localization of Multiple Invasive Fish

In this paper, we study a problem encountered during our ongoing efforts to locate radio-tagged fish aggregations with robots. The problem lies at the intersection of search-based methods whose objective is to detect a target, and active target localization methods whose objective is to precisely localize a target given its initial estimate. Real-world sensing constraints such as limited and unknown range, large measurement time, and ambiguity in bearing measurements make it imperative to have an intermediate initialization phase to transition from search to localization.We present a local search strategy aimed at reliably initializing an estimate for a single target based on observations from field experiments.We then extend this strategy to initialize multiple targets, exploiting the proximity of nearby aggregated tagged fish to decrease the cost of initialization per target. We evaluate the performance of our algorithm through simulations and demonstrate its utility through a field experiment where the robot successfully detects, initializes and then localizes nearby targets.

Comparison of Foraging Performance of Diploid and Triploid Saugeyes (Sauger × Walleye)

Abstract To evaluate the performance and quality of triploid saugeyes (female walleye Stizostedion vitreum × male sauger S. canadense), we compared their foraging behavior with that of diploid conspecifics. Triploidy was induced by heat-shocking fertilized eggs for 15 min at 31°C 5 min after fertilization, and ploidy was evaluated by flow cytometry. In three experiments using both ploidy groups we evaluated (1) prey selection with respect to fathead minnow Pimephales promelas and the daphnia Daphnia pulex; (2) aggression and food consumption by individual saugeye predators during a single feeding session; and (3) handling time of a single large (50-60% of predator body length) minnow. Juvenile diploid saugeyes foraged more successfully than triploid conspecifics. Diploids caught fathead minnow significantly more frequently than did triploid fish (59% and 39% of available minnow, respectively) while consuming significantly fewer daphnids. Triploids fed on zooplankton to a larger extent. Experiment 2 reveal...