Predation by tiger muskellunge on bluegill: Effects of predator experience, vegetation and prey density

Many pellet‐reared tiger muskellunge (F1 hybrid of female muskellunge Esox masquinongy and male northern pike E. lucius) do not survive stocking in reservoirs dominated by bluegill (Lepomis macrochirus) prey. Poor survival may occur because few hybrids capture bluegills. In a previous study done in hatchery ponds, only 10% of naive hybrids (those never before exposed to live prey) captured bluegills during 15 days. In similar ponds, we tested the effects of predator experience (using hybrids previously exposed to bluegill prey), vegetative cover, and bluegill density on the number of hybrids capturing prey. Few experienced or naive hybrids captured bluegills at low prey density, regardless of the presence or absence of vegetation. When bluegill density was increased from 1 to 5 prey/m2 in ponds or to 40/m2 in aquaria, many hybrids captured bluegills. Our pond study suggests that most hybrids will not fare well when stocked in lakes where only bluegill forage is present.

Effects of turbidity on prey selection and foraging rate of hatchery-reared juvenile tiger muskellunge

Tiger muskellunge (northern pike Esox lucius × muskellunge E. masquinongy ) are stocked into aquatic systems across North America to control undesirable fish species or to create sportfishing opportunities. Because decreased water clarity can affect the poststocking foraging ability of an ambush predator like the tiger muskellunge, we evaluated the effects of turbidity on the foraging success of tiger muskellunge in a laboratory setting. We tested prey selectivity and total prey consumption by juvenile tiger muskellunge at four turbidity levels (Secchi depths of >84, 53, 26, and 18 cm) using three prey species: goldfish (Carassius auratus) (a surrogate for common carp Cyprinus carpio ), gizzard shad Dorosoma cepedianum , and green sunfish Lepomis cyanellus . Tiger muskellunge consumed significantly less prey at Secchi depths of 26 and 18 cm than at a Secchi depth of >84 or 53 cm. Selectivity for or against all prey types decreased as turbidity level increased, such that all the shad were positively selected and goldfish were negatively selected in clearer water. green sunfish were neutrally selected at all turbidity levels tested. These results suggest that increasing turbidity levels will negatively impact prey encounters and consumption rates, which likely will reduce growth rates of tiger muskellunge, ultimately reducing fish survival and stocking success.

Strike feeding behavior in the muskellunge (Esox masquinongy): Contributions of the lateral line and visual sensory systems

The muskellunge (Esox masquinongy) is a predatory esocid fish with well-developed visual and lateral line systems. The purpose of this study was to determine the relative roles of these two sensory modalities in organizing the strike behavior of the animal. Subadult muskellunge were videotaped in a test arena while feeding on fathead minnows (Pimephales promelas). Animals were tested under five conditions: (i) control animals in which the visual and lateral line systems were intact; (ii) animals with lateral line afference suppressed by immersion for 12–24 h in 0.1 mmol l(−1) CoCl2; (iii) animals blinded by bilateral optic nerve transection; (iv) animals that had been unilaterally blinded; and (v) animals in which the lateral line system had been unilaterally denervated. The feeding behavior of the muskellunge consists of two phases: a slow stalk of the prey with minimal body movement followed by an explosive C- or S-start lunge at the prey. Quantitative comparisons of animals in the five test groups indicate that, although vision is used in the initial acquisition of the prey, both vision and the lateral line system play important roles in determining the initiation of the rapid strike. The lateral line system may play a critical role in the final capture of the prey at the end of the strike. In addition, lateral-line-suppressed muskellunge strongly alter their approaches to more distant prey. Bilaterally blinded muskellunge do not stalk their prey, but will lunge only at prey that are at close range. Unilaterally blinded or denervated muskellunge also alter their detection of and approach to prey, attending to a wider region of the intact sensory hemisphere. Our data suggest not only that the visual and lateral line systems play complementary roles in the feeding behavior sequence but also that each system plays a more or less dominant role during consecutive phases of the behavior.

Tiger muskellunge predation on stocked salmonids intended for recreational fisheries

Hatchery-reared fish are stocked widely to enhance recreational fisheries but are often consumed by predators. Stable isotope analyses were used to evaluate tiger muskellunge (northern pike [Esox lucius] × muskellunge [E. masquinongy]) predation on stocked salmonids (Oncorhynchus) relative to naturally reproducing white suckers (Catostomus commersonii), in 5 Colorado reservoirs. Stable isotope analyses coupled with a mixing model using a Bayesian framework indicated that tiger muskellunge primarily consumed stocked salmonids (53–84% by mass). These results suggest that stocking salmonids into systems that contain tiger muskellunge (and potentially other predators) may result in losses of valuable stocked fish. Further, the use of tiger muskellunge or other piscivores as biological control of less desirable species to benefit sympatric salmonid populations may be counterproductive to management goals. Finally, this study demonstrates the potential for managers to use this framework as a tool to identify and evaluate unintended losses of fishes to piscivores in other systems.

An experimental approach to determine esocid prey preference in replicated pond systems

Competitive interactions between salmonids and white suckers (Catostomus commersonii) often result in poor salmonid growth, condition, and ultimately angler catch-per-unit-effort. Fisheries managers frequently introduce hybrid northern pike (Esox lucius) and muskellunge (E. masquinongy), known as tiger muskellunge, as biological control agents to reduce the abundance of undesirable species including white suckers, while simultaneously attempting to create viable recreational fisheries with stocked salmonids. In this study, northern pike were used to evaluate esocid prey preference between naïve, hatchery-reared rainbow trout (Oncorhynchus mykiss) and wild white suckers. Enclosures containing northern pike were stocked with rainbow trout and white suckers at 2 densities (50:50 and 20:80, respectively) to represent different ratios of forage. Weekly sampling by beach seine was used to determine rainbow trout and white sucker mortality. When the experiment was complete, enclosures were drained to determine overall survival of the forage species. Rainbow trout numbers declined precipitously to zero, while 60–75% of white suckers remained across all treatments. This study demonstrated a clear difference in survival of rainbow trout and white suckers (rainbow trout having lower survival) in the presence of northern pike under these conditions. We suggest fisheries managers consider these findings when stocking or managing for piscivores to control undesirable fish species, or to create recreational fisheries, while simultaneously stocking naïve sport fish vulnerable to predation.

Feeding strategies of young-of-the-year muskellunge from two large river ecosystems

We analyzed stomach contents from 674 young‐of‐the‐year (age‐0) muskellunge (Esox masquinongy) sampled in New York waters of the St. Lawrence and upper Niagara rivers to (1) describe diets and document use of nonnative prey, (2) examine the feeding strategy (generalized versus specialized) and the importance of different prey types, (3) evaluate temporal patterns in feeding strategy and prey importance, and (4) determine how prey length related to muskellunge length and whether this relationship differed among prey types. Banded killifish Fundulus diaphanus , native cyprinids, and tessellated darters (Etheostoma Olmstedi) were the most important prey numerically and by weight in the St. Lawrence River. Native cyprinids, banded killifish, and darters (Etheostoma spp. and Percina spp.) were the most important prey in the Niagara River, but nonnative cyprinids were more important by weight than darters. Muskellunge from both rivers exhibited a specialized feeding strategy, with individuals specializing on different prey types. The muskellunge feeding strategy and the prey types of greatest importance were consistent among years and among months within years. The relationship between prey length and muskellunge length differed among prey types: as muskellunge length increased, lengths of laterally compressed, spiny prey increased at a slower rate than did the lengths of fusiform prey. Mean prey length as a proportion of predator length declined with increasing muskellunge length in the St. Lawrence River but was constant in the Niagara River. In the St. Lawrence River, prey length as a proportion of predator length decreased for all prey types except cyprinids, for which length was a constant proportion of predator length. Our results can be used to guide evaluations of prey fish assemblages at muskellunge nursery sites and to prioritize sites as candidates for protection, restoration, or use as stocking locations.

Predation by pellet-reared muskellunge on minnows and bluegills in experimental systems

Studies in Wisconsin lakes have shown that stocked tiger muskellunge (F1 hybrids of female muskellunge, Esox masquinongy x male northern pike, E. lucius) reared on live food survive better than those reared entirely on dry pellet food. We evaluated the ability of pellet‐reared hybrids to convert to a minnow (Notropis spp. and Pimephales promelas) or bluegill (Lepomis macrochirus) diet in laboratory aquaria and hatchery ponds. In aquaria, 86–310‐mm (total length) tiger muskellunge selected cyprinids that were about 40% of their own length and bluegills that were about 30% of their length, sizes closely predicted by an optimal foraging construct (time from prey capture to complete prey ingestion ÷ prey dry weight). Using these prey sizes, we tested hybrids (130, 150, and 170 mm long) in conversion experiments in aquaria and ponds. During experiments, prey were maintained at a constant density and predators were sampled periodically to determine the proportion eating fish. Tiger muskellunge converted more slowly to bluegills than to minnows in both aquaria and ponds. In aquaria, 85% of the hybrids converted from pellets to minnows by day 3, whereas only 68% converted to bluegills. By day 5, conversions to minnows and bluegills were 95% and 82%, respectively. In ponds, 73% of the hybrids converted to minnows by day 5 and 89% by day 14. No hybrids had eaten bluegills by day 3 and only 53% converted by day 14. The apparently limited ability of pellet‐reared tiger muskellunge to switch to a bluegill diet may influence survival and growth of these predators in reservoirs dominated by a centrachid forage base.

Comparison of mouth morphology and prey size selection among three Esocid taxa

Aquatic organisms, especially fishes, exhibit exceptional diversity in mouth morphology and this variation has been shown to influence foraging patterns. We compared mouth morphology among muskellunge (Esox masquinongy), northern pike (Esox lucius) and their hybrid, tiger muskellunge (E. masquinongy x E. lucius). Head and mouth size among the three taxa were similar for juveniles (<400 mm total length), but diverged with increasing length, being greater for northern pike than muskellunge. Tiger muskellunge had a head and mouth size intermediate to the two, but more similar to northern pike than muskellunge. Morphological differences among taxa were related to data examining prey size selection in laboratory and field experiments. In the laboratory, northern pike selected prey that were smaller than their maximum mouth width (widest point between outside corners of mouth), tiger muskellunge selected larger prey, and muskellunge size-selection was intermediate between the other two taxa. Among the three esocids, muskellunge had the smallest increase in handling time with increasing prey body depth relative to predator mouth width. In a common garden field experiment in three lakes containing mainly deep-bodied prey, results generally followed morphological patterns, with northern pike selecting larger prey compared to muskellunge. Although morphology predicted most of the variation in greatest body depth of prey consumed, the best predictor of prey size was a model that included predator mouth width, taxon, and interaction. Information comparing prey size selection among esocid taxa is useful for understanding how to manage esocid populations based on system-specific prey characteristics and also for understanding how variations in morphological characteristics of apex predators can influence prey vulnerability and ecosystem structure.

Food selection of muskellunge fry

Five genera of invertebrates, collected from a municipal sewage lagoon, were fed to muskellunge (Esox masquinongy) fry for 23 days. The fry preferred Moina brachiata during both day and night (1300 and 2300 h) and Cyclops vernalis at night; they did not prefer Asplanchna sieboldi, Potamocypris sp., and Daphnia spp. Organisms in the foregut of fry collected at 2300 h were significantly larger, but not more numerous, than those in the foregut of fry collected at 1300 h. As the fry grew and the mouth width increased, the size of ingested organisms increased. Fry initially selected the first and second instars of M. brachiata and tended to avoid the later instars and adults; by day 23 they selected adults over immature instars. Immature and adult M. brachiata appeared to be of adequate size to feed muskellunge fry during alimentary canal development.

Diet of striped bass and muskellunge downstream of a large hydroelectric dam: A preliminary investigation into suspected Atlantic salmon predation

Top predators, such as the Striped Bass (Morone saxatilis ) and Muskellunge (Esox masquinongy) , can impact food webs and alter ecosystem structure through the regulation of prey populations. Within the Saint John River, New Brunswick, Canada, both predators have long been hypothesized to impart significant mortality on smolts of the endangered Atlantic Salmon (Salmo salar ). As a consequence, current management practices entail euthanizing Muskellunge (an introduced species) that enter fish passage facilities along the Saint John River. Furthermore, the recovery and protection of a native Striped Bass population have largely been ignored. To assess seasonal diet, gastric lavage was performed on Striped Bass (n = 244) and Muskellunge (n = 96) captured in the downstream proximity of the Mactaquac Dam from April to November 2016. Clupeids dominated the stomach contents by number (92% for Striped Bass; 49% for Muskellunge) and mass (71% for striped bass; 96% for muskellunge). Other prey species included white perch (Morone americana) , yellow perch (Perca flavescens) , American shad (Alosa sapidissima) , and American eels (Anguilla rostrata) . No Atlantic Salmon smolts or other regionally recognized recreational fish species were identified in any of the stomach samples (n = 340) examined. Concurrently, this study observed little temporal overlap between the smolt migratory period and the arrival of Striped Bass to the Mactaquac Dam. Some Striped Bass (n = 33) were observed to be in spawning condition, releasing eggs and milt when handled, although reproduction by this species in the Saint John River was thought to have ceased long ago.