Document Category: Stocking and Transfers

We assessed predator acclimation as a technique to improve the poststocking survival of juvenile muskellunge (Esox masquinongy) and tiger muskellunge (muskellunge × northern pike E. lucius ) in laboratory, pond, and lake experiments. For all experiments, a subset of esocids was exposed to feeding largemouth bass (Micropterus salmoides) (250–300 mm total length). In laboratory pools containing simulated vegetation (50% of pool), we tested the vulnerability of predator‐acclimated and naive muskellunge and tiger muskellunge to largemouth bass predation. For both species, survival rates were similar regardless of predator experience. Predator‐acclimated esocids, however, spent more time in the vegetation, indicating that exposure to predators may alter some behaviors. We also introduced equal numbers of naive and predator‐acclimated tiger muskellunge into ponds and lakes containing largemouth bass. To determine the number of surviving fish, ponds were drained after 7 d, whereas lakes were sampled immediately after stocking and throughout the fall. We found similar survival rates between naive and predator‐acclimated individuals, suggesting that predator acclimation techniques that are successful with other species are not effective in reducing losses of stocked muskellunge and tiger muskellunge.

From an ecological perspective, predation, competition or resource partitioning, and abiotic factors interact to affect species distribution and abundance. To make management recommendations, I review research dealing with the relative influence of these factors in determining stocking success of muskellunge (Esox masquinongy). Survival of stocked muskellunge is affected by losses to resident predators. Prey preference and composition are also important, and better muskellunge survival and growth occurs in systems with soft‐rayed or fusiform prey rather than in centrarchid‐dominated systems. However, potential for competition with resident fishes has not been carefully considered. Abiotic factors, particularly temperature, can influence stocking mortality and subsequent growth. Survival increases with size and is maximized with large muskellunge fingerlings (>240 mm), but cost‐effectiveness can vary substantially with predator and prey populations. Hatchery rearing techniques can also affect muskellunge stocking success. Pellet‐reared fish have lower survival than minnow‐reared fish because predation mortality is higher, but both groups exhibit similar food consumption and growth. The parental population can affect survival and growth because temperature‐related differences in bioenergetic variables occur among muskellunge populations. In addition to compromising genetic integrity, the mixing of populations with different physiological characteristics may have negative consequences for native populations. Thermal regimes of recipient waters should be considered in choosing the most appropriate population for stocking outside the native range. Muskellunge stocking should be pursued within an ecological context that integrates the relative importance of predation, competition, and abiotic factors. This framework provides a guide for making management decisions concerning populations, hatchery rearing techniques, sizes, and timing of muskellunge introductions into systems with specific characteristics.

Intraspecific seasonal and diel variation in movement behaviours of three stocks of juvenile (age-2; 399-610 mm total length) muskellunge (Esox masquinongy) were assessed using radio telemetry in Forbes Lake (225 ha), Illinois, USA. Experimental populations included muskellunge from the upper Mississippi (Leech Lake, Minnesota) and Ohio (Cave Run Lake, Kentucky) river drainages, as well as progeny from North Spring Lake, Illinois, a mixed origin stock. No differences in hourly movement rates or home rages were detected among stocks. Movement rates were greatest during spring (mean ± SE = 42 ± 4 m/hr), lowest during summer (16 ± 3 m/hr) and intermediate in autumn (28 ± 5 m/hr). Additionally, movement rates during the summer were greater at night than crepuscular periods. Home range sizes were similar during spring and autumn (mean ± SE = 17-18 ± 3-4 ha) and decreased during summer (5 ± 3 ha). Although habitat selection characteristics were generally similar among stocks, fish from the upper Mississippi River drainage occupied deeper water more frequently and selected the pelagic zone more strongly during the spring that those from the Ohio River and mixed origin stocks. Within the littoral zone, muskellunge selected coarse woody habitat and aquatic macrophytes. Collectively, these findings suggest little behavioural differentiation among genetically divergent stocks when evaluated in a common reservoir environment.

We evaluated direct and indirect effects of feeding experience on growth, food consumption, susceptibility to predation, and survival of esocids. We conducted five experimental stockings of equal numbers and similar sizes (200 mm) of experienced (minnow‐fed) and naive (pellet‐fed) muskellunge (Esox masquinongy) (two stockings) and tiger muskellunge (muskellunge × northern pike (E. lucius) ; three stockings) in reservoirs. Feeding experience had no direct influence on prey consumption and growth. Food consumption was similar in laboratory pool experiments. In contrast, experienced esocids exhibited higher fall survival than naive fish of both taxa. Feeding experience indirectly affected survival, because predation by largemouth bass (Micropterus salmoides) was higher on naive esocids. Examination of potential mechanisms in field and laboratory experiments suggested predation vulnerability was not affected by differences in habitat selection, foraging behavior, antipredatory behavior, or dispersal. Color pattern between minnow‐ and pellet‐fed fish differed in both absolute color and contrast between light and dark markings, which may influence susceptibility to predation. Our results suggest that feeding experience can affect survival of introduced fish.

We examined survival, predation mortality, growth, and prey consumption for three sizes of fingerlings of muskellunge (Esox masquinongy) after stocking. Small (100 mm total length), medium (200 mm), and large (250 mm) fingerlings were introduced into each of three reservoirs over 3 years. Fall survival, based on population estimates and electrofishing catch per unit effort, was lowest for small fingerlings and increased with fingerling size. Across all reservoirs, survival of large fingerlings was 2–3 times that of medium fingerlings. Cost‐benefit analyses showed large fingerlings to have the lowest cost per survivor. Predation by largemouth bass (Micropterus salmoides) decreased with fingerling size at stocking. Both foraging success and growth of stocked fingerlings were correlated with prey density. In contrast, prey species composition did not appear to influence foraging success or growth. Because they were stocked earlier, medium fingerlings achieved a greater size than did large fingerlings through the first fall when prey density was high but not when prey density was low. To maximize survival, growth, and cost‐effectiveness, we recommend stocking large muskellunge fingerlings in systems with high prey and low largemouth bass densities.

We used creel and draining censuses to measure angling catch, harvest, and hooking mortality of tiger muskellunge (female muskellunge Esox masquinongy × male northern pike E. lucius ) in a 6. l ‐hectare Illinois impoundment dominated by largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) . The vulnerability of tiger muskellunge to angling produced a substantial catch‐and‐release fishery: 226 hybrids stocked in 1981 and 1982 were caught 388 times (1.7 times per fish) during four fishing seasons, and 27 others were recovered in the draining census in 1985. Only four legal fish (≥762 mm in total length) were harvested, but this number might have increased to 29 (13% of the number stocked) if the minimum‐length limit had been reduced to 710 mm. Strict enforcement of a 762‐mm minimum‐length limit failed to generate a productive and cost‐effective trophy fishery, because growth was slow and many hybrids died from natural or hooking mortality before they reached legal size, The cost of each trophy fish harvested at Ridge Lake was prohibitively high (US $100); a more reasonable investment of about $1.00 was required for each fish that contributed to the catch‐and‐release fishery. More than 40% of the hybrids stocked in 1981 and 1982 survived the first winter, and at least 19% were alive in April 1985. Twelve percent of tiger muskellunge caught by anglers died within 24 h of capture, Hooking mortality increased as water temperature increased and was greater in the last year of the study (22%) than in the previous 3 years (8–10%). Hooking mortality was not affected by type of bait (live or artificial) or size of fish. Predation by tiger muskellunge on bluegill did not reduce bluegill density and hence had no apparent effect on growth, size structure, or angling catch of bluegill.

The survival and growth of 4, 8 and 12 inch muskellunge (Esox masquinongy) fingerlings stocked at the rate of 4/acre in four northern Wisconsin lakes in 1976 and 1977 were investigated. Fish from the six separate stockings were given a distinctive fin clip and data on survival and growth were obtained in subsequent electrofishing and fyke netting collections.

In Arrowhead Lake, in all three size groups survival was similar for fish stocked in 1976 but for those stocked in 1977 survival was highest for 12 inch fingerlings. Survival was also highest for the 12 inch fingerlings stocked in Branch and Johnson lakes in both years, but in Sparkling Lake survival was negligible both years for all stocked fingerlings. Growth in Arrowhead Lake was better than growth of fingerlings in hatchery rearing ponds. The good survival and growth of fingerlings stocked in Arrowhead Lake may be attributed to the low density of northern pike and other predators and an abundant supply of your-of-year yellow perch (Perca flavescens), a good potential food source.

Small muskellunge fingerlings (4 inches) can contribute to a sport fishery when stocked in a lake with a low density of predators and a good supply of suitable forage. Where moderate – large northern pike populations exist it is recommended that only larger (12 inches) fingerlings be stocked.

Four-, eight-, and twelve inch muskellunge fingerlings were stocked at the rate of 4/acre in four Vilas County lakes in 1976 and 1977, and their subsequent survival and growth were evaluated. Short- and long-term survival of all three size groups was similar in Arrowhead Lake for fish stocked in 1976, while short-and-long-terms survival for muskellunge fingerlings stocked in Arrowhead Lake in 1977 was highest for stocked 12 inch fingerlings. Survival was also highest for the 12 inch fingerlings stocked in Branch and Johnson lakes in both 1976 and 1977, while survival of all three size groups in Sparkling Lake was negligible both years. Growth of the muskellunge fingerlings stocked in Arrowhead Lake was better than the growth of fingerlings in hatchery rearing ponds. The good survival and growth of fingerlings stocked in Arrowhead Lake can probably be attributed to the low density of northern pike and other potential predators and an abundant supply of you-of-the-year yellow perch in 1976 and 1977.The yellow perch probably provided a food source for the stocked muskellunge and served as a buffer from would-be predators. This study indicated that small muskellunge fingerlings (approximately 4 inches) can contributed to a sport fishery when stocked in a lake with a low density of predators and a good supply of suitable forage. It is recommended that only large (12 inches or larger) fingerlings be stocked where there is a moderate-to=large northern pike (predator) population.

Understanding the genetic and evolutionary impacts of stocking on wild fish populations has long been of interest as negative consequences such as reduced fitness and loss of genetic diversity are commonly reported outcomes. In an attempt to sustain a fishery, managers implemented nearly five decades of extensive stocking of over a million Muskellunge (Esox masquinongy ), a native species in the Lower St. Lawrence River (Québec, Canada). We investigated the effect of this stocking on population genetic structure and allelic diversity in the St. Lawrence River in addition to tributaries and several stocked inland lakes. Using genotype by sequencing, we genotyped 643 individuals representing 22 locations and combined this information with forward simulations to investigate the genetic consequences of long‐term stocking. Individuals native to the St. Lawrence watershed were genetically differentiated from stocking sources and tributaries, and inland lakes were naturally differentiated from the main river. Empirical data and simulations within the St. Lawrence River revealed weak stocking effects on admixture patterns. Our data suggest that the genetic structure associated with stocked fish was diluted into its relatively large effective population size. This interpretation is also consistent with a hypothesis that selection against introgression was in operation and relatively efficient within the large St. Lawrence River system. In contrast, smaller populations from adjacent tributaries and lakes displayed greater stocking‐related admixture that resulted in comparatively higher heterozygosity than the St. Lawrence. Finally, individuals from inland lakes that were established by stocking maintained a close affinity with their source populations. This study illustrated a benefit of combining extensive genomic data with forward simulations for improved inference regarding population‐level genetic effects of long‐term stocking, and its relevance for fishery management decision making.