The influence of spawning habitat on natural reproduction of muskellunge in Wisconsin

Many of Wisconsin’s native populations of muskellunge Esox masquinongy exhibit declining reproductive success and failing natural recruitment. As a result, self‐sustaining populations of muskellunge are diminishing. This study focused on spawning habitat factors that influence egg development and survival and, consequently, the reproductive success of muskellunge. Muskellunge spawning habitat characteristics in lakes with self‐sustaining populations were compared with spawning habitat characteristics in lakes that were once self‐sustaining but are now maintained by stocking. The hatching success of artificially fertilized eggs was assessed under natural lake conditions. Spawning sites were typically marshy areas in water less than 1 m deep. Characteristics of the spawning habitat influenced successful reproduction. Spawning areas in stocked lakes had low dissolved oxygen (DO; 1.2–5.4 mg/L) at the substrate–water interface, whereas self‐sustaining lakes had more variable DO (0.5–9.6 mg/L) with some microhabitats having high DO. Organic carbon content, texture of spawning substrate, and water temperature at the substrate did not differ between self‐sustaining lakes and lakes supported by stocking. Fallen logs, stumps, and other wood in spawning areas may increase egg survival. Muskellunge egg survival over natural substrate was low (0.0–1.3%), even in lakes with self‐sustaining populations. Collections of eggs and observations of fry indicated that major mortality occurred after egg deposition but before fry reached nursery habitats several weeks after hatching.

Fine scale features of muskellunge spawning grounds in Georgian Bay

Loss and degradation of spawning habitat has been identified as a major stressor in the widespread decline of muskellunge (Esox masquinongy) populations. Protection of spawning habit has therefore been designated a management priority and research is needed to permit efficient identification of these areas. One avenue of research has been to model spawning habitat based largely on the characteristics of spawning sites (i.e., locations where confirmed spawning events have occurred). However, characterization of more general spawning grounds remains comparatively unexplored. We analyzed radio telemetry data collected from three regions of Georgian Bay (from southeastern to northern Georgian Bay) to determine if adult muskellunge have predictable, fine scale movement patterns when using spawning grounds. A total of 49 individuals were tracked for up to three spawning seasons during 2012-2015. Both male and female muskellunge exhibited staging behavior during the spawning season and appeared to travel along areas with moderate slopes (between 1° and 10°). Females staged further offshore in deeper waters (maximum depth ranged from 1.7 to 2.9 m) and were consistently more mobile than males. By comparison, males staged in shallower waters (maximum depth ranged from 1.3 to 2.6 m) towards the offshore edges of coastal wetlands and wait at access points for females to move inshore to spawn. In all three regions of Georgian Bay we found adult muskellunge staging in water deeper than what has typically been defined as spawning sites (>1.5 m) making brief forays into shallower areas to spawn. We suggest that deeper areas and moderately sloping areas used as travel corridors are important components of spawning grounds that need to be protected in addition to the typical shallow wetland areas where muskellunge actually spawn.

Structural complexity influences littoral coarse woody habitat selection by juvenile muskellunge

Coarse woody habitat (CWH) is an important feature of aquatic systems, offering foraging opportunities, refuge from predation, and spawning habitat. Fish abundance and diversity have been positively correlated with the density of CWH in aquatic systems through manipulative or laboratory experiments; however, less is known about how structural complexity of individual CWH units influences fish use. To explore how fish relate to a gradient of available CWH complexities in a field environment, we evaluated selection of CWH complexities by stocked, juvenile muskellunge (Esox masquinongy) in Forbes Lake, Illinois, using radiotelemetry. Most (86%) CWH in Forbes Lake was simplistic, consisting of a single trunk with no or few primary branches, whereas only 9% of the CWH was structurally complex, possessing most or all primary and secondary branches. Muskellunge used all available CWH complexities but selected for intermediate complexity, even though that represented only 5% of the available habitat; all other CWH complexity classes either were used in proportion to abundance or were avoided. Selection by muskellunge of intermediate CWH complexity may represent trade‐offs among prey availability, predator foraging efficiency, and refuge from predation. As impounded reservoirs across the muskellunge range continue to age and lose habitat complexity, managers engaged in habitat restoration should consider the potential effects of CWH complexity on fish use.

Identification of principal spawning areas and seasonal distribution and movements of muskellunge in Leech Lake, Minnesota

Six specific muskellunge spawning locations were documented and preferred spawning habitat was determined by surgically implanting radio transmitters in 14 adult muskellunge capture by angling in summer 1979. Adult fish from each of thre areas on the lake were radio-tagged. Spawning sites were distinctly offshore in depths of 1 to 2 m over a soft calcareous substrate with Chara spp. as the dominant vegetation. Physical characteristics of the six examined areas were very similar even though widely separated geographically. Selection for these sites occurred even though a wide variety of habitat types was available. Mean tracking time for 12 fish was 396 days which included the 1980 spawning period. Significant differences relating to home range and movement were observed for muskellunge inhabiting disparate environments within the lake. Muskellunge residing tin the main basin occupied total home ranges which were five times larger than of those fish inhabiting Walker Bay. The main lake fish also tended to have winter home ranges distinctly separate from summer ranges and winter home ranges were larger than summer ones by a factor of nearly two. Walker Bay fish had winter home ranges which were smaller than those of summer by a factor of over six and were contained within the summer ranges. Survival of all angler-caught fish additionally subjected to implant surgery strongly suggest that catch and release of muskellunge is a realistic management option.

Lake characteristics influencing spawning success of muskellunge in northern Wisconsin lakes

We determined the physical, chemical, biological, and land use characteristics that distinguish northern Wisconsin lakes with self‐sustaining populations of muskellunge Esox masquinongy from lakes where stocking is required to maintain populations. Lakes that supported self‐sustaining muskellunge populations were characterized by fewer shoreline alterations and by spawning habitats with softer, organic‐nitrogen‐rich sediments. Lakes that required stocking had extensively developed shorelines. The direction of water level change during the spawning period, percentage of spawning area sediment covered by woody debris, number of deadfall trees per kilometer of shoreline, and percentage of shoreline that was totally developed were the most important variables for classifying the level of muskellunge reproduction a lake could support. A linear discriminant function correctly classified 83% of the lakes with self‐sustaining muskellunge populations and 89% of the lakes requiring stocking to sustain or enhance muskellunge populations. Lake managers wishing to use muskellunge stocking programs to reestablish self‐sustaining populations should critically review each candidate lake by considering our model and that of Dombeck et al. (1986).

Mortality, dispersal and habitat use of stocked juvenile muskellunge in two western North Carolina rivers

The Muskellunge (Esox masquinongy) is a highly sought‐after sport fish that is native to the Tennessee River drainage of western North Carolina. After the extirpation of Muskellunge from North Carolina in the 1950s, the North Carolina Wildlife Resources Commission began a stocking program to re‐establish the species and produce viable Muskellunge fisheries in North Carolina. Although stocking efforts have created a Muskellunge fishery in, for example, the French Broad River (where the species was native), there is little evidence of success in North Carolina sections of the New River (where the species was not native). Possible mechanisms inhibiting stocking success are unclear because there is relatively little information available on the juvenile life stage of the Muskellunge, especially in the southern portion of its distribution. We addressed the perceived differences in recruitment between the two fisheries by using telemetry to investigate dispersal, mortality, and habitat use by stocked juvenile Muskellunge. Fifty hatchery‐reared, age‐0 Muskellunge (282–307 mm TL) were tagged prior to stocking in the New River (fall 2013) and French Broad River (fall 2014). Three months after stocking, known survival of tagged fish was 4% in the New River and 29% in the French Broad River; the survival probability after 3 months was estimated at 9% (range = 4–17%) in the New River and 37% (range = 25–56%) in the French Broad River. Extended survival in the French Broad River was 14% at 252 d post-stocking. High dispersal was observed, with maximum individual dispersal of 67.4 km in the New River and 55.5 km in the French Broad River. Habitat suitability analyses indicated that juvenile Muskellunge in the FBR selected shallow nearshore areas with low water velocity, fine substrate, and substantial cover in the form of woody debris and overhanging vegetation. Information on the survival and behavior of stocked Muskellunge can facilitate efforts to successfully manage these fisheries.

Muskellunge spawning site selection in northern Wisconsin lakes and a GIS-based predictive habitat model

Spawning habitat degradation has been linked to declines in naturally reproducing Muskellunge (Esox masquinongy) populations, and managers require efficient methods to identify and protect these habitats. We collected spawning habitat data from 28 lakes in northern Wisconsin to determine Muskellunge spawning habitat selection and to create a GIS‐based model for predicting the locations of spawning sites. Spawning site selection by Muskellunge may be more complex than previously thought. Muskellunge showed selection for spawning in habitats with a sheltered effective fetch and east‐facing shorelines. The strongest selection was for habitats with a combination of moderate slope, small flats, and concave bathymetric curvature. Muskellunge selected against steeply sloping shorelines; very large areas of shallow flats; developed shorelines; herbaceous wetlands; and complex‐leafed submersed aquatic vegetation. Lake trophic status appears to interact with other habit variables to determine spawning site selection; sites without submersed aquatic vegetation were more strongly selected in eutrophic lakes than in other lake types. A GIS model of spawning site selection was created using the machine learning program MaxEnt (Maximum Entropy Modeling). The model predicted that Muskellunge would spawn in areas with moderately sheltered effective fetches, moderate to small areas of shallow flats, away from outflowing streams, and (to a lesser extent) along shorelines facing east or west. The model was tested on novel lakes using area‐under‐the‐curve (AUC) analysis, in which values ranged from 0.5 (predictions no better than random) to 1.0 (perfect assignment). The mean AUCtest value (i.e., the expectation of model performance for a novel lake) was 0.637 (SD = 0.12). When the model was used to designate the best 20% of available spawning habitat area for Muskellunge in each lake (based on the relative probability of spawning), that area contained 32% of the spawning sites. The model provides an efficient method for management agencies and conservation groups to use in designating spawning habitat for conservation and in communicating with the public through spawning habitat maps.

Quantification of native muskellunge habitat: Influence of body size, fish community composition and vegetation structure

Habitat utilization of native young-of-the-year (YOY) muskellunge, Esox masquinongy, was quantified by the type and density of vegetation present, water depth, and fish communities associated with their presence and abundance in nursery bays of the Upper St. Lawrence River. We completed 441 seine hauls and captured 400 YOY muskellunge in 11 bays that were sampled each July and August over a 3-year period (2002–2004). We hypothesized a change in habitat utilization related to increasing body size, as YOY muskellunge doubled in total length from July to August. Fine-leafed submerged and emergent macrophytes and prey availability (cyprinids, Notropis sp., banded killifish, Fundulus diaphanous and tessellated darter, Etheostoma olmstedi), were positively related to muskellunge use in July, while in August coverage of broad-leafed submerged macrophytes and increased overall vegetation density were the best habitat descriptor. In both months, muskellunge were associated with moderate (20–60%) vegetation coverage and density, however, captures were in areas of significantly greater vegetation coverage and density than was generally available. A negative relation of muskellunge occurrence with water depth, yellow perch, Perca flavescens, and stonewort, Chara vulgaris, was observed in both months. The negative relationship between muskellunge and depth, plus their strong linkages to nearshore submerged vegetation and forage fish that inhabit the nearshore areas, highlights the importance of protecting the ecological integrity of nearshore habitats. Our findings should assist managers in protecting native stocks, planning restoration and enhancement initiatives, and in regulating riparian and nearshore development

Managing spawning and nursery habitat of the Georgian Bay muskellunge (Esox masquinongy)

The following Ph.D. describes how a period of sustained low water levels and shoreline modifications in Georgian Bay, Lake Huron, have impacted the coastal wetland habitat used by muskellunge during their early life. To counteract these adverse effects, the thesis provides a definition of the wetland features that promote the survival of youngof-the-year muskellunge in Georgian Bay. Included is a proposed management tool in the form of an Index of Nursery Habitat Suitability (INHS) for muskellunge that can be used to identify high-quality, early-life habitat of muskellunge. Furthermore, the INHS can be used to predict how the quality of this habitat responds to different water-level scenarios and to shoreline modification in Georgian Bay, and to guide rehabilitative efforts of degraded wetland habitat.

Unique Georgian Bay nursery habitat features allows for successful habitat differentiation: Steps towards a spatially explicit muskellunge nursery habitat suitability index model

In Ontario, muskellunge (Esox masquinongy) management strategies are predicated on self-sustaining populations to ensure high quality trophy fisheries. These strategies provide safeguards for breeding adults and their spawning habitats. In Georgian Bay, Lake Huron, suitable spawning habitat appears pervasive given the Bay’s oligotrophic status. However, after more than a decade of sustained low water levels and increases in shoreline modification, coastal wetland nursery habitat structure has been altered for which muskellunge young-of-the-year (YOY) are sensitive. Thus, despite the presence of suitable spawning habitat, muskellunge populations may fail is suitable nursery habitat is limited or absent. This hypothesis was supported in southeastern Georgian Bay where suitable muskellunge spawning habitat failed to support YOY from a lack of suitable nursery habitat structure and altered fish community. Unfortunately, very little information exists that can help managers identify suitable nursery habitat in Georgian Bay which may be more limiting to recruitment and spawning habitat. To address this knowledge gap, a region in northern Georgian Bay was sampled for YOY muskellunge during 2012-13 to describe and quantify habitat parameters related to muskellunge nursery habitat in the absence of shoreline modification. Multivariate statistical techniques successfully differentiated muskellunge nursery sites from available habitat. Results suggested that suitable muskellunge nursery habitat in Georgian Bay encompassed a relatively narrow range of habitat parameters characterized by: steeper substrate slopes, greater densities and diversity of upper water column structuring submerged aquatic vegetation (SAV) and relatively low densities of low growing SAV. Muskellunge nursery habitat characteristics also p4romote a more diverse fish community and limited abundances of yellow perch (Perca flavescens) than sites absent of YOY muskellunge. These results are forming the basis of a spatially explicit muskellunge nursery Habitat Suitability Index (HIS) model for Georgian Bay. This HIS can nbe used in conjunction with current management strategies to provide a more holistic, complementary approach to managing muskellunge populations by accounting for the life stage habitats limiting to recruitment.