Mark-recapture studies are an important component of fisheries research and management. Underlying assumptions of such studies include minimal tag loss and negligible effects on the behavior, fitness, and survival of tagged individuals. Passive integrated transponder (PIT) tags are becoming increasingly commonplace, largely because of their small size, ease of implantation, longevity, and reportedly high rates of retention. We evaluated tag retention and survival and growth effects on age-0 muskellunge Esox masquinongy marked with PIT tags at two implantation sites, the peritoneal cavity and the dorsal musculature, during overwinter trials in Illinois and Wisconsin. For both trials, no significant differences in survival (88.0-89.8%), relative daily growth (0.0006-0.00062 mmÁmm À1 Ád À1 ), or tag retention (99.5-99.8%) were observed among the two implantation groups and a control group. Survival and tag retention were also similar between trials. Our findings suggest that PIT tags implanted either in the peritoneal cavity or the dorsal musculature are acceptable for use in marking age-0 muskellunge.

Intraspecific, seasonal and diel variation in movement behaviours of three stocks of juvenile (age-2; 399-610 mm total length) muskellunge, Esox masquinongy Mitchill, were assessed using radio telemetry in Forbes Lake (225 ha), IL, USA. Experimental populations included muskellunge from the Upper Mississippi (Leech Lake, MN, USA) and Ohio (Cave Run Lake, KY, USA) river drainages, as well as progeny from North Spring Lake, IL, a mixed-origin stock. No differences in hourly movement rates or home ranges were detected among stocks. Movement rates were greatest during spring (mean ± SE = 42 ± 4 m h )1 ), lowest during summer (16 ± 3 m h )1 ) and intermediate in autumn (28 ± 5 m h )1 ). 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 than 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. K E Y W O R D S : behaviour, intraspecific variation, muskellunge introductions, stocking program, stocks, telemetry.

No abstract

Muskellunge Esox masquinongy are broadly distributed across the northern United States and southern Canada. Intraspecific genetic variation suggests the existence of divergent stocks related to residence in major river drainages. Populations and stocks have likely adapted to specific environmental conditions associated with geographic location, especially latitude and the associated thermal regime. In this study, we examined differences in survival and growth among stocks of juvenile Muskellunge stocked into lakes throughout Illinois. Muskellunge from the Ohio River drainage stock, the upper Mississippi River drainage stock, and the current mixed Illinois broodstock were used for comparisons. Stocking mortality was related to temperature and was greatest for Illinois and Ohio River drainage fish that were stocked during the early fall. Mississippi River drainage fish experienced high mortality over the first summer after stocking, resulting in the lowest abundance during the second fall poststocking. In addition to low catch rates, Muskellunge from the Mississippi River drainage were significantly smaller than fish from the Illinois and Ohio River drainage stocks by the second fall. Populations from similar latitudes and climate (Illinois and Ohio) performed the best in terms of survival and growth and should be utilized in future stockings. Received October 7, 2016; accepted March 15, 2017 Published online May 4, 2017

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.Received July 5, 2013; accepted August 27, 2014

We evaluated the effects of fin‐clipping on the foraging behavior and growth of age‐0 muskellunge Esox masquinongy. Fish were subjected to one of six fin‐clipping treatments (one or both pectoral and pelvic fins, all paired fins, and a nonclipped control) and allowed to forage on golden shiners Notemigonus crysoleucas in laboratory pools (1.7 m in diameter). Observations of foraging behavior showed that muskellunge required a similar number of stalks, follows, and strikes to capture prey regardless of fin clip. Capture efficiencies (56%) were also similar among treatments. In outdoor pools (1.5 m in diameter), the growth and food conversion efficiency of fin‐clipped muskellunge feeding on golden shiners over a 1‐month period did not differ from those of unclipped controls. Fin removal did not compromise foraging behaviors and growth for juvenile muskellunge foraging on moderately evasive prey, and fish showed immediate behavioral compensation.

Genetic differences among muskellunge Esox masquinongy populations are related to residence in major river drainages, suggesting the existence of divergent stocks. By use of radiotelemetry we compared different seasonal and diel temperature selection in a southern Illinois reservoir for three geographically and genetically distinct stocks of age-2 muskellunge from throughout the latitudinal range of the species. Muskellunge from the Upper Mississippi River drainage were represented by the Leech Lake, Minnesota, population and the Ohio River drainage was represented by the Cave Run Lake, Kentucky, population. Progeny from North Spring Lake, Illinois, an interstock, or mixedorigin stock, were also evaluated. No differences in temperature selection were observed among stocks of juvenile muskellunge across seasons or diel periods. The seasonal mean temperatures of the water varied significantly-spring 21.7°C, summer 28.4°C, and fall 14.8°C, with an overall average temperature of 24.1°C, in agreement with previously published values obtained in laboratory trials. This lack of different temperatureselection patterns among stocks is in contrast with other life-history characteristics, for example growth, metabolism, and conversion efficiency, which have been shown to differ among populations and stocks.

Intraspecific genetic variation across the distribution of MuskellungeEsox masquinongy suggests the existence of divergent stocks among major river drainages. Often, stocks differentiate in response to latitudinal variation in thermal regime. Genetic variation and thermal adaptation may drive fish to either maximize growth during brief growing seasons at higher latitudes (countergradient growth) or experience longer periods of slower growth at lower latitudes (cogradient growth). The strength and direction of these genetic effects matter for fish stocked outside of their native drainage and for populations experiencing changes to regional thermal regimes. We used a replicated pond experiment with uniform initial fish size and environmental conditions to compare the survival and growth of stocked age-0 Ohio River drainage (OH) Muskellunge with those of the more northerly upper Mississippi River drainage (MISS) stock following their first winter and a year after introduction into a common environment. Both stocks had similarly high winter survival, though the MISS stock had a slower growth rate overwinter than the OH stock. Survival during the latter spring-to-fall period was greatly reduced for the MISS stock, however, with the differences in growth rate persisting. These findings suggest that cogradient adaptation to temperatures experienced during early life stages in native environments results in a disadvantage for high-latitude stocks of Muskellunge in thermal regimes warmer than those they have historically experienced in their native drainages.