Muskellunge Management: Fifty Years of Cooperation Among Anglers, Scientists, and Fisheries Biologists

<em>Abstract</em>.—A population assessment of Muskellunge <em>Esox masquinongy </em>in two connected north-central Minnesota lakes allowed evaluation of angler data when assessing various population metrics, including the residual effects of historical stocking efforts, as a nonlocal strain had been introduced into the native population during the 1970s. In 2012, the Minnesota Department of Natural Resources sampled and marked Muskellunge using trap nets during the prespawn and spawning periods and electrofishing during the postspawn period, while anglers collected data from fish caught during the 2012 open-water season. Anglers released all fish after collecting a scale for genetic analysis. Microsatellite DNA genotypes were used to differentiate individuals, thus identifying recaptures, and to estimate ancestry derived from the stocked strain. Anglers reported catching 16% of individuals marked by biologists. Of Muskellunge reported by anglers, 78% were from the lake where they were initially captured while 22% were reported in the lake opposite their initial capture. Postspawn movements suggested that more individuals migrated from the lake characterized as having preferred spawning and nursery habitat to the lake characterized as having preferred summer habitat and prey. The age- and length-frequency distributions of fish captured by anglers and trap nets were similar, while electrofishing sampled younger and smaller fish, likely because it occurred postspawn when many adults had moved off shore. The best estimate of adult population size was produced by a model incorporating fish length as a covariate. Density was estimated at 0.70 adults per ha or 1.92 adults per littoral ha. Higher percentages of nonlocal ancestry were associated with smaller maximum size potential (<em>L_</em>∞ ) in von Bertalanffy growth models. Our study described key population characteristics for a Muskellunge population while demonstrating that anglers could reliably collect several specific types of data that supplement data collected by management agencies.

Muskellunge Management: Fifty Years of Cooperation Among Anglers, Scientists, and Fisheries Biologists

<em>Abstract</em>.—The identification, protection, and restoration of spawning habitat for Muskellunge <em>Esox masquinongy </em>in Green Bay, Lake Michigan are vital steps for re-establishing a self-sustaining population. This study was designed to locate spawning areas, document and model spawning habitat preferences, assess natural recruitment, and determine if suitable habitat was found throughout Green Bay (Fox River, lower Green Bay, Menominee River, and Little Sturgeon Bay). Radio transmitters were inserted into the oviduct of mature female Muskellunge prior to spawning and expelled transmitters were later located using radio telemetry to identify spawning locations. Between 2009 and 2010, 26 of 37 (70%) implanted transmitters were located as deposited at spawning locations. Using identified spawning locations, habitat selection was estimated for key environmental variables, and MaxEnt (maximum entropy) was utilized to model Muskellunge spawning habitat in the Menominee River, as it was the only study area where natural reproduction was documented. Menominee River Muskellunge showed significant preferences for spawning in areas with shallow bottom slopes (5%), with medium-to-high submerged aquatic vegetation coverage (>33%), where coarse woody debris was present, and where dominant substrates were sand or cobble. MaxEnt modeling predicted a ~2.5 magnitude greater likelihood of spawning at an average spawning location compared to an average background location. Comparisons of available habitat among study areas showed the Menominee River contained more spawning habitat with preferred characteristics. Results from this study are important steps in identifying spawning habitat as a potential limiting factor to successful Muskellunge reintroduction and models could be used to locate suitable areas to stock and guide delineation of critical spawning habitat to designate for protection.

Muskellunge Management: Fifty Years of Cooperation Among Anglers, Scientists, and Fisheries Biologists

<em>Abstract</em>.— Long-term research indicates a significant and ongoing decline within the upper St. Lawrence River Muskellunge <em>Esox masquinongy </em>population. Index surveys show a sharp reduction in catch of both spawning adults and age-0 Muskellunge, and catch rates by anglers have similarly declined while harvest remains low. Other changes associated with population decline include presence of fewer female adult Muskellunge and a change in adult Muskellunge size structure (increase in proportion of fish <1,016 mm) in addition to more large individuals greater than 1,372 mm. A significant adult die-off occurred from 2005 to 2008 (103 adults recovered in U.S. and Canadian waters) concomitant with an outbreak of viral hemorrhagic septicemia (VHS). These population changes were also temporally correlated with detection and proliferation of invasive Round Goby <em>Neogobius melanostomus</em>, a known VHS virus (VHSV) reservoir, egg predator, and competitor with native fishes. Comparisons of index netting before and after VHSV and Round Goby invasions suggest a direct link to the decline, but because these are correlations, we can only explore these effects. To examine the viability of Muskellunge nursery sites, we repeated survival studies conducted in the early 1990s with experimental releases of advanced fry at four locations during 2013–2015. Findings indicate contribution to age-0 populations, but catches poststocking (wild and stocked) were lower compared to the 1990s. We review information regarding potential stressors, including VHSV and Round Goby invasion, and conclude that their combined effects have created significant uncertainty and challenges to sustainable management of the Muskellunge population. In response, the St. Lawrence River Muskellunge management plan should be updated with a focus on restoration of the declining Muskellunge stock. Recommended actions target advancing conservation and restoration of critical habitat, restoring lost subpopulations, and reducing mortality associated with angling (e.g., from handling and harvest).