Illinois Muskies

Seasonal Movement and Habitat Use of Muskellunge in a Southern Illinois Reservoir

Patrick A. Beck*¹ and Ronald C. Brooks

Department of Zoology

Fisheries and Illinois Aquaculture Center

Southern Illinois University Carbondale

pbeck@siu.edu

rbrooks@siu.edu

*Corresponding author: pat.beck@tpwd.state.tx.us

¹Present address: Texas Parks and Wildlife, District 3C Inland Fisheries,11810 FM 848, Tyler, TX 75707, USA

Keywords: Muskellunge, temperature, habitat use, movement
Synopsis- Kinkaid Lake is located in southern, Illinois, and was initially stocked with Muskellunge in 1985. There is a paucity of information concerning movement and habitat use in the southern portion of the Muskellunge’s expanded range. We used ultrasonic telemetry to determine seasonal movement and habitat use of adult Muskellunge (965 mm to 1,250 mm TL). Movement was variable among seasons and individuals. The highest movement rates (>13 km wk-1) were observed during prespawn (February) and summer (June) periods. When surface water temperatures exceeded 25°C (mid to late summer), tagged Muskellunge were often (> 50% of the locations) located at depths where dissolved oxygen concentrations were less than 3 mg L-1, and minimal movement (<1 km wk-1) was observed. The study Muskellunge used available habitats in a similar manner for all seasons excluding fall. Additionally, tagged Muskellunge exhibited a selection for specific habitats during all seasons.

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Muskellunge Esox masquiongy are highly-valued sportfish because of their trophy-size potential, unique fighting abilities, and their elusive behavior. They are endemic from the St. Lawrence and Hudson River drainages west through the Great Lakes, the upper Mississippi basin (mostly east), and the Ohio basin (Crossman 1978). As a result of their popularity, the species has been introduced into many lakes and reservoirs beyond their native range.

Although research has been conducted to examine Muskellunge movement and habitat use in more northern latitudes, we could find no published reports of movement behavior or habitat use throughout the seasons in the southern extent of their endemic or expanded ranges. Understanding how this coolwater species adjusts its behavior in a warmwater environment would benefit biologists considering stocking reservoirs located at more southern latitudes.

Kinkaid Lake is Illinois’s southernmost reservoir stocked with Muskellunge. Warm air masses produced in the Gulf of Mexico often flow into the extreme southern portion of Illinois. Consequently, the region's ambient temperature cycles are more comparable to central Arkansas than central Illinois. Winter ice cover on the lake is minimal to nonexistent, and summer surface water temperatures can exceed 30°C for extended periods. The relatively mild winters and prolonged periods of hot, summer weather in southern Illinois make Kinkaid Lake an excellent environment to study seasonal Muskellunge movement and habitat use where ambient characteristics are similar to those near the southern extent of their range.

During summer, it is possible that the combination of thermal stratification and high water temperatures constrain or eliminate availability of quality Muskellunge habitat. Adult Muskellunge typically seek water temperatures at 25.6° C, and their preferred temperatures decline with age or size (McCauley & Huggins 1979). Thermal stratification occurs in Kinkaid Lake throughout the summer; a strong thermocline develops at approximately 3-4 m by early June. Water temperatures are at their highest levels during late June and persist through mid September, and dissolved oxygen is often insufficient at depths where temperatures are optimal or preferred by Muskellunge. Since the Muskellunge’s upper lethal limit is near 30°C (Scott and Crossman 1973), these conditions potentially create a thermally stressful environment for Kinkaid Lake Muskellunge.

Observing adult Muskellunge during summer may identify behavioral adaptations that allow the them to survive. Additionally, seasonal movement and habitat use in the warmer environment likely vary from Muskellunge located in colder, more endemic environments. The objectives of this study were to examine seasonal movements and habitat use of adult Muskellunge in Kinkiad Lake, Illinois and examine behavior during potentially stressful summer periods.

Study Site

Kinkaid Lake, located in Jackson County, Illinois, was constructed in 1968 as a municipal water supply reservoir by building a dam to flood a portion of the Shawnee National Forest. The reservoir has an approximate surface area of 1,100 hectares, a mean depth of 9.0 m, and a maximum depth of 27 m. The lake has two distinct areas (Figure 1). The Johnson Creek area is turbid and shallow with diverse habitats of timber and vegetation. It is comprised of several shallow timber bays bordered with water willow Justicia americana extending out to approximately 1 m and water milfoil Myriophyllum spicatum in deeper areas. Creek channels extend from the back of many fingerlike coves and connect to the main creek channel (Johnson Creek) which meanders through the entire length of Kinkaid Lake. The main basin is oligotrophic ; deep and clear with diverse habitats of dense water milfoil, timber, rip rap shorelines, deep coves, and island chains. Beds of water milfoil often extend from shore to depths of approximately 5 m. Road beds, bridge abutments, and submerged foundations are present throughout the area. Most of the reservoirs' coves contain fairly dense areas of standing timber, regardless of the water depths. Substrates are variable and may be comprised of muck, sand, gravel, rock, or a combination of these.

Kinkaid Lake supports a large fish community. In addition to Muskellunge, the sportfish community includes several Centrarchids, Percids, Ictalurids, and Moronids. Non-game fishes include Sciaenids, Catastomids, Cyprinids, Clupeids, and smaller Ictalurids. Muskellunge fingerlings of variable sizes have been stocked semi-annually to annually in Kinkaid Lake since 1985. During the last several years, 2,000 age-0 fingerlings have been stocked annually during September. No natural reproduction has been documented in the lake.

Methods

Ultrasonic transmitters (V16T-6H-S256, 69.0 KHZ, 20-69 sec, Vemco, Shad Bay, Nova Scotia) were surgically implanted into 12 large (>1,000mm TL) Muskellunge in Kinkaid Lake during spring 2003 (Table 1). The ultrasonic transmitters were 106 mm x 16 mm and weighed 16 g in water. Each transmitter contained a temperature sensor with an accuracy of ± 0.12 C.

Muskellunge were collected in cooperation with the Illinois Department of Natural Resources (IDNR) during spring trap netting surveys. We implanted transmitters in six fish collected in the Johnson Creek area and six in the main basin area. All fish were tagged and released at the capture site (Figure 1). Muskellunge were collected and transferred individually from a trap net into a holding tank where they were anesthetized using carbon dioxide at concentrations of approximately 300 mg L-1 (Summerfelt & Smith 1990). Dissolved oxygen concentrations of at least 5 mg L-1 were maintained using compressed oxygen. Once anesthetized, the Muskellunge were placed in an inclined surgical tube containing enough water to submerge the gills (Strand 1986). All surgical equipment was sterilized with alcohol. The tags were implanted into the abdominal cavity through an incision on the ventral side of the fish anterior to the pelvic fin. The incision was closed with three to four closely spaced 3-0 monofilament sutures using the simple interrupted technique. Upon completion, the Muskellunge were transferred to a recovery tank until equilibrium was restored, and they were released.

Movement

Tracking commenced two weeks following capture and was attempted every third day, when possible, through spring 2005. Fish locations were determined using a Vemco VR-60 receiver and a VH-10 directional hydrophone. All fish were located, or the entire lake was searched, on each tracking day. Tracking was conducted during daylight hours. Upon locating a fish, transmitter temperature was recorded. YSI 550A temperature and dissolved oxygen meters were used to identify depth (temperature) that matched respective individual body temperature, thus obtaining fish depth. Temperature and dissolved oxygen profiles were measured at four fixed sites and at individual fish locations from the water surface to bottom in 0.5-m increments. Other habitat characteristics were recorded such as lake depth at location, and Secchi depth.

The vast differences in environmental conditions throughout the Muskellunges range make a standard season difficult to define. The mild winters and extreme summer heat of southern Illinois are not indicative conditions found throughout the Muskellunge’s endemic range. Hence, for all statistical analysis (including habitat use) we defined seasons as follows: December, January, and February (winter), March, April, and May (spring), June, July, and August (summer), and September, October, and November (fall). Behavior during potentially stressful summer periods were examined separately in order make comparisons during periods when no thermal stress was evident and to compare their behavior to native populations at northern latitudes.

The coordinates of each fish location were recorded using a differentially corrected global positioning system (Garmin 168S). Fish locations were overlaid onto lake maps using ArcMap 9.1. Distances between locations were generated with SAS (Little et al. 1996) using the Pythagorean relation. Reference coordinates were inserted onto lake maps to account for distances that were not line of sight. Distances (m day-1) between successive locations represent minimum distance the fish had traveled. Variation in movement of tagged Muskellunge was analyzed with a mixed model analysis of variance. In the model, seasons were regarded as fixed effects, while interactions between fish and season were treated as random effects. Additionally individual fish were regarded as the sampling unit (Rogers 1998; Otis and White 1999). Bonferroni multiple comparison tests were used for seasonal and monthly movement comparisons. The Bonferroni method limits the overall experimentwise error rate by testing each comparison using a significance level of α" = α /k: where α equals error rate and k equals the number of comparisons (Sokal and Rohlf 2001). By utilizing this method we reduce the probability of making a type I error while keeping statistical significance at p<0.05.

Habitat Use

Habitat maps were created using a Garmin 168s and ArcMap 9.1. Habitat was characterized as one of four categories: open water (devoid of vegetation), standing timber, vegetation, or a combination of vegetation and standing timber. Vegetation in Kinkaid is primarily water milfoil with a fringe of water willow. Other species exist only in trace amounts; therefore, vegetated habitats were not segregated by species. The specific habitats defined were located on-site, habitat dimensions were marked, and coordinates were recorded. After field evaluation, individual habitat polygons were created with the recorded coordinates and with the aid of digital raster graphic (DRG) topographic maps obtained from the Illinois Natural Resources Geospatial Clearinghouse (http://www.isgs.uiuc.edu/nsdihome/) using ArcMap 9.1. Detailed habitat availability maps were then overlaid with a 25 X 25 m raster grid map to quantify available habitat (acres) using ArcMap 9.1. Individual fish observations were overlaid to calculate frequency of habitat use.

Variation in habitat use associated with individual tagged fish was maintained by using the individual fish as the sampling unit (Otis and White 1999). A likelihood chi-square test was conducted to determine habitat selection by testing the null hypotheses: H₀(1): tagged fish were uniformly distributed using the available habitat in a similar way (i.e. differences in use frequency among tagged fish), and H₀(2): habitat use was in proportion to availability (i.e. selection). To test the first null hypothesis (whether fish are using habitats in a similar fashion) we used the equation presented by Manly et al. (2002): if: u_ij equals the amount of habitat type i used by fish j; u_i+ equals the amount of type i habitat used by all fish; u+_j equals the total amount of habitat units used by fish j; and u++ equals the total number of habitat units used by all fish, then the log-likelihood test statistic is:

Χ_L₁² = u_ij ln (u_ij / (E u_ij))

where E (u_ij) = u_i +u+ _j u++.

The obtained value suggests that fish are using habitats differently if the value obtained is large in comparison with the chi-square distribution (Manly et al. 2002). In addition, a significant p-value (α =0.05) allows one to conclude that tagged fish are using the habitat differently.

Determination of habitat selection (second null hypothesis) was tested using the same parameters but with a modified equation; where E (u_ij) = π_i u+ _j, with π_i equal to the proportion of the population of available units in habitat type i. A resulting large value and significant p-value indicate a selection of habitat choices. Difference between the two chi-square values, along with significant p-value indicate, on average, if fish are selecting specific habitat types (Manly et al. 2002).

When selection was demonstrated, selection ratios were used to identify the specific habitat type selected (Manly et al. 1972; Hobbs and Bowden 1982; Manly et al. 2002). By using selection ratios, insights involving habitat use at the population level can be obtained. Manly et al. (2002) estimated the ratio to be Ŵ_i = (u_i +) / (π_j u++). This selection ratio, designated as Ŵi, is a measure of the proportion of habitat used over the proportion of habitat available. The method described above allows the population as a whole to determine the selection ratio, while still preserving individual fish variation (Manly et al. 2002). Selection for a certain habitat type is determined with values above 1, while avoidance was assumed by values below 1. Bonferroni confidence intervals were constructed for each ratio to test the significance of the value (Thomas and Taylor 1990).

Results

Two of the twelve Muskellunge inserted with transmitters were located within a few days of post implantation but were never relocated. The ten remaining fish were located on 743 occassions from April 2004 through May 2005 (Table 1). Fish recaptured by anglers, electrofishing, or trap-netting had well-healed incisions from transmitter implantation, and there were, presumably, no adverse physiological effects on fish behavior.

Temperatures

Surface water temperatures ranged from 5˚C to 33°C but varied little throughout summer (range = 27° - 33°C). Fall and spring surface temperatures were variable, with ranges of 12° to 27°C and 8° to 27°C, respectively. Winter surface temperatures ranged from 5° to 12°C, and ice cover did not occur in the main basin. Thermal stratification in Kinkaid Lake occurred from the mid May through mid November at depths ranging from 4.5 m to 6.5 m. Dissolved oxygen was limiting (<3 mg L-1) below the thermocline during June through September. Dissolved oxygen in deeper water continually increased through October until the lake became isothermic by mid November.

Muskellunge body temperatures varied among seasons with fluctuating water temperatures (Figure 2). October through December body temperatures ranged from 5°C to 22°C, and since the lake was essentially isothermic, they were very near surface water temperatures ( 7°C - 20°C). During late December through February, Muskellunge body temperatures ranged from 4°C to 11°C and were cooler than surface temperatures. Dissolved oxygen limited the lower limits of water temperatures Muskellunge inhabited (22°C to 29°C) during June through September. During that period, Muskellunge maintained body temperatures near 25°C when the water temperatures occurred at depths where suitable dissolved oxygen concentrations were available; thus Muskellunge were usually located at water depths associated with the thermocline. Once surface temperatures cooled in September, Muskellunge were always located at depths where dissolved oxygen concentrations were greater than 3.0 mg L-1.

Muskellunge often inhabited water temperatures that would be considered stressful to coolwater fish species during July and August, or alternatively, they were located at depths containing very low dissolved oxygen concentrations; possibly to avoid the warmer water (Figure 3). Dissolved oxygen concentrations of less than 3.0 mg L-1 were occupied by tagged fish 50% of the time during the two summer months. Thirty percent of the locations were at depths where dissolved oxygen ranged from 3.0 mg L-1 to 5.0 mg L-1 contained in a very narrow transitional zone. In that zone, dissolved oxygen levels usually dropped from 3.0 mg/L to less than 1 mg/L in a depth of less than 0.5 m (e.g. from depth of 3.0 m to 3.5 m). The remaining 20% of the Muskellunge locations were in temperatures at or above 28°C where higher dissolved oxygen concentrations were present. However, when we continually monitored individual Muskellunge located in the very warm water to determine whether or not they were holding in the warm water, we found that they typically moved to cooler water after very short periods.

Movement

Distances traveled by the Muskellunge varied among individuals. Some Muskellunge established seasonal home ranges within a relatively defined portion of Kinkaid Lake, and the home ranges often overlapped with those of other tagged fish. Some of the Muskellunge moved throughout the lake during most of the year. Fish that did not to establish smaller or more specific home ranges tended to use particular areas of the reservoir whether or not it was in another Muskellunge's home range. The wanderers would move from one particularly popular area, stay in another, and later move to yet another area where Muskellunge were frequently located. The temporary destinations did not appear to differ from many other areas in the lake, in terms of habitat types, lake depths, or contours.

During late February and early March, all of the fish moved in a migratory fashion into the shallow Johnson Creek area. Several moved well up into Kinkaid Lake's primary tributary (Johnson Creek) for a short period and then retreated back into the reservoir's Johnson Creek area. The amount of time that the fish remained in the Johnson Creek area varied from several weeks through June. Two fish remained in the lower, deeper portion of the Johnson Creek area during most of the study period.

Despite the individual variability in movement, seasonal patterns were evident. When water temperatures were highest, movement was least and visa versa (Figure 2). Mean movement for all fish throughout the study period was 452 m day-1 and ranged seasonally from 624 m day-1 in winter to 331 m day-1 in spring (Figure 4). Movement rates were statistically lower during spring than all other seasons (p≤0.01).

Within season variation of movement was examined to reveal if specific months affected seasonal movement comparisons (Figure 5). Mean daily movements were statistically significantly higher during February (916 m day-1) than all other months except June (750 m day-1) during which the Muskellunge movement was significantly higher than in May, July, and August (p≤0.05). During July, Muskellunge moved an average of 92 m day-1 which was less than any other month. No differences occurred among months during fall and spring (p≥0.05).

When we examined average distances traveled, it was apparent that the summer movement rates were significantly elevated by a two to three week period in June when, in the last week, Muskellunge averaged 11,276 m day-1 (Figure 6). Movement averaged approximately 300 m day-1 for eight weeks prior to mid-June and only 180 m day-1 during the six-week period following June.

Habitat

The two chi-square tests indicated selection for certain habitat types in all seasons, and selection ratio estimates identified differences in types of habitat used among seasons. The first chi-square test (χ_L1²) identified differences in habitat use among implanted Muskellunge. Individual tagged Muskellunge exhibited similar habitat use patterns during winter (χ _L1²32.52, df 52, p≥0.05), spring (χ_L1 ²58.12 df 108, p≥0.05), and summer (χ_L1²45.30, df 117 p≥0.05). During fall, habitat use varied among transmitter fish (χ_L1² 74.88, df 36, p≤0.01). The second chi-square test (χ_L2²) was used to provide further evidence for selection of habitat types used but does not identify specific types of habitat. The test indicated that despite heterogeneity in fall habitat use among the transmittered Muskellunge, individual fish selected for specific habitat types (χ_L2²291.12, df 40 p≤0.01).

Fall selection ratio estimates indicated a preference for combined (timber and vegetation) habitats (10.768), and to a lesser degree, vegetation (1.300) with an avoidance of timber (0.879) and open water (0.357)(Table 2). During winter, Muskellunge were selective in the types used (χ_L2²110.79, df 56 ≤0.001) largely preferring timber (2.488) over other habitat types. Muskellunge selected for specific habitats occupied in spring (χ_L2²156.02, df 120 p=<0.001) and summer (χ_L2²166.34, df 130 p≤0.01). During spring, Muskellunge selected solely for timber (2.808), and in summer for vegetation (1.929) and combined habitats (4.925).

When the lake was temperature stratified and fish depth (actual suspended depth) was obtainable (late spring through early fall), Muskellunge were typically located (and most often suspended) at depths of 3.4-3.7 m. Fish depth did not differ statistically among seasons or months (p≥0.05). The average lake bottom depth at the areas of Muskellunge locations varied among seasons from 4.1 m in spring to 8.3 m in winter. Muskellunge occupied mean lake depths of 6.2 -9.3 m in summer. During spring, Muskellunge were located in mean lake depths of 4.1 m -5.4 m.

Discussion

Water temperature has been shown to be an important factor in Esocid movement (Casselman 1978, Cook & Bergersen 1988, & Younk et al. 1996). Muskellunge exhibit distinct seasonal or temperature related behavior in terms of movement patterns and habitats frequented in all areas of their distribution (Crossman 1977, Miller & Menzel 1986, Strand 1986, Crossman 1990, Hanson & Margenau 1992, Margenau 1994, Younk et al. 1996, Tipping 2001). However, depending upon the season, movement reported for the fish in more northern latitudes often differed from those exhibited in Kinkaid Lake.

Although Kinkaid Lake temperature cycles are similar to endemic lakes at more northern latitudes, temperature extremes are not. There were no periods of ice cover in Kinkaid Lake, and water temperatures only decreased to a minimum of 5°C during a few weeks in winter in the reservoir; whereas, more northern lakes often sustain ice cover for months. The exact opposite is true during summer months when temperatures within the epilimnion at Kinkid Lake will often exceed 30°C for extended periods. The differences in temperature extremes that occur during summer and winter appear to alter Muskellunge's behavior in terms of movement and habitat use.

Minor & Crossman (1978) documented minimal movement of adult Muskellunge during winter in a large lake in central Ontario. Dombeck (1979) found similar results in two northern Wisconsin lakes. In contrast, Kinkaid Lake Muskellunge had higher average movement rates during winter than in all other seasons - though statistically similar to all other seasons but spring. The lack of reduction in winter movement can likely be attributed to the mild nature of winters in southern Illinois.

Despite the short duration of cold, winter weather, Kinkaid Lake Muskellunge behaved similarly to those in more northern latitudes during late winter through early spring. They a moved towards potential spawning areas when water temperatures rose above 5°C, which is typical for Muskellunge. In Wisconsin, Muskellunge spawn at temperatures ranging from 9° to 15° C (Dombeck 1979; Gammon 1986). a similar temperature range existed from the last week of March through the second week of April in the Johnson Creek area of Kinkaid Lake. The shallow, turbid, northern end of the Johnson Creek area and the major tributary (Johnson Creek) that empties into Kinkaid Lake are perceived to be spawning areas. Tagged Muskellunge frequented this area throughout the month of February and well into March.

Kinkaid Lake Muskellunge remained in shallow areas of the Johnson Creek basin until it warmed considerably when compared to the rest of the lake; exceeding 20° C by May. At that time, most of the Muskellunge moved only a short distance to a deeper portion of the basin. In West Okoboji Lake, IA, Miller & Menzel (1986) reported an increase in movement when surface temperatures increased to 16° C; considered a transitional period between spring and summer. Kinkaid Lake Muskellunge did not display a similar increase in movement until June when surface water temperatures approached 25°C; the temperature preference for adult Muskellunge by (Oehmcke et al. 1958, Scott & Crossman 1973, Minor & Crossman 1978, & Dombeck 1979). Casselman (1978) also found activity to be greatest at or near Muskellunge thermal preference in laboratory experiments. The increased movement in June also underscored the end of late spring through early summer behavior.

Muskellunge movement was drastically reduced once surface temperatures exceeded 30° C in July (Figure 6). No Muskellunge studies with surface temperatures greater than 26° C exists to our knowledge; however Miller and Menzel (1986) also reported reduced movement or activity at maximum surface temperatures for Muskellunge in West Okoboji Lake, IA, Conversley, Younk et al. (1996) found movement of Muskellunge in the Upper Mississippi River to increase during summer months. In Kinkaid Lake, summer water temperatures exceeded 25° C near the thermocline which was established around 4-5 m, and there were no habitats available within Muskellunge's reported preferred temperatures. Limitations in dissolved oxygen concentrations at suitable temperatures restricted movement of Muskellunge during summer months and may have caused the fish to inhabit warmer water than they would have preferred.

During the aforementioned summer periods when water temperatures were most extreme, Muskellunge in Kinkaid Lake often selected for cooler temperatures with low dissolved oxygen concentrations rather than utilizing abundant oxygen at warmer water temperatures. In a southern Ohio Reservoir, Headrick & Carline (1993) presumed suitable habitat for northern pike to be water temperatures less than 26°C with dissolved oxygen greater than 3 mg L-1. During their study, northern pike selected for cooler temperatures, but dissolved oxygen concentrations below 3.0 mg L-1 only accounted for 10% of their locations. As fish age and grow, there is a tendency to use deeper cooler water (McCauley & Huggins 1979). The northern pike in Headrick & Carline's study were less than 1,000 mm in length and less than 5 years old. In our study, greater than 50% of the large Muskellunge were located at depths with less than 3.0 mg L-1 dissolved oxygen during summer months.

Other cool and cold water species have been stocked outside their native ranges with similar behavioral responses to summer conditions. Striped bass Morone saxatilis, rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta were restricted to the coolest water available with adequate dissolved oxygen concentration (Cheek et al. 1985; Mathews et al.1985; Coutant 1990; Barwick et al. 2004). Coutant (1985) referred to this situation as a “squeeze”. In his studies, striped bass in Tennessee reservoirs were forced to occupy habitats considered unsuitable (or at least incompatable) in terms of temperature and dissolved oxygen, with physiological demands or preferences. Thus, survival of cool or cold water species in warm water reservoirs depends upon the persistence of an ever shrinking thermocline during summer months.

Underwater springs or incoming streams may provide areas of thermal refugia in otherwise warmwater reservoirs (Moss 1985). Prior to this study, it was presumed underwater springs were present in Kinkaid Lake and provided relief to extreme summer water temperatures; however, telemetry and temperature/depth profiles did not lead to a discovery of these areas. Consequently, based on previously cited reports for trout and striped bass, summer water temperatures higher than the Muskellunge preferred caused reduced movement and likely physiological stress. In Kinkaid Lake, restricted movement occurred despite the fact that water temperatures during our study period were not as severe as during most summers in the region.

Habitat use by Muskellunge varied among seasons in Kinkaid Lake. Spring habitat use was comprised of mostly open water and timber, but due to the differences in percent habitat availability, the Muskellunge selected only for timber. Timber areas inhabited by the study Muskellunge in early spring were located primarily near the back of timber coves and at the shallow, northern end of the Johnson Creek area. Shallow areas are the first areas to begin warming, and gizzard shad (the primary Muskellunge prey species in Kinkaid Lake) congregate to feed there.

After the initial early spring warm up, Kinkaid Muskellunge gradually moved into deeper water mostly within the Johnson Creek area. Gizzard shad had also moved into those areas, and the Muskellunge's behavior indicated an increase in foraging as a searching predator. Miller & Menzel (1986) assumed Muskellunge to be searching predators after spawning through mid-summer.

During summer, Muskellunge have a preference for vegetated areas (Oehmcke et al. 1958, Scott & Crossman 1973). Vegetation or combination habitats (timber and vegetation) were also selected by Kinkaid Lake Muskellunge in summer when the two habitats represented 60% of the observations (Figure 7). Once fish settled into their summer areas, the fish exhibited little movement activity, and their depth did not vary. Warm surface temperatures and limited dissolve oxygen may have restricted the activity of the fish, but residing in vegetation allows fish to maximize feeding success without exerting high amounts of energy. Metabolism of the fish increased with water temperature and movement making it vital to their survival to maximize the foraging success, while minimizing movement.

During fall, although individual Muskellunge selected for habitats differently from one another, overall, they selected mostly for combination habitats. Concentrated use of weed line habitats inundated with timber provided evidence that Muskellunge were using these areas to feed on forage species frequenting these areas. Muskellunge are thought to be ambush predators most of the time. The percent of observations in vegetation and open water, along with variable depths occupied in fall by Kinkaid Lake Muskellunge, suggest that some were ambush predators while others were searching predators (Figure 7). Fall could be a transitional period where Muskellunge shift from an ambush to a searching predator. This was also suggested by Miller & Menzel (1986) due to behavior that exhibited high levels of activity, long displacements, and variable distributions in water depths.

This study provided insight to Muskellunge behavior in terms of movement and habitat use in an environment with warmer seasonal temperature extremes than are normally inhabited by the coolwater species. Behavior by Kinkaid Lake Muskellunge during extreme periods of winter and summer differed from those located at more northern latitudes. During the summer periods, it was evident that there were prolonged periods when high water temperatures combined with low dissolved oxygen were causing the fish to inhabit less than desirable conditions, thereby altering behavior. Future research needs to be conducted to determine the affects of stress induced to the Muskellunge during these periods and whether the stress causes decreases in overall condition. If this were the case, temperature-induced stress could reduce growth rates, interfere with egg maturation or development, and even cause death to adult Muskellunge before they could grow to trophy sizes.

Acknowledgments

We would like to thank the Shawnee Muskie Hunters and Muskies Inc. for aid in project funding. We also appreciate the help and courtesy extended by the Illinois Department of Natural Resources and their involvement in this study, with special thanks to Shawn Hirst, Steve Pallo, and Steve Kreuger. Completion of this study could not have been possible without the help of researchers at the Southern Illinois University Fisheries and Illinois Aquaculture Center. Assistance provided by Nick Wahl and Doug Schultz was instrumental to the completion of this project. Finally, we appreciate contributions by Roy C.Heidinger, Edward J. Heist, and Robert M. Neumann.

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