Terry L. Margenau

Factors Affecting Growth of Northern Pike in Small Northern Wisconsin Lakes

Abstract Fish assemblages that include northern pike Esox lucius as a dominant predator were sampled in 19 small (<120 ha) northern Wisconsin lakes. The purpose of this sampling was to describe northern pike population characteristics and identify factors affecting growth rates. Fish assemblages in these lakes were dominated by centrarchids, primarily bluegill Lepomis macrochirus, and small fusiform species such as yellow perch Perca flavescens. Northern pike population size structures were typically truncated at around 53 cm. Average density of northern pike (≥35 cm) was 16.1 fish/ha and ranged 2.8–38.0 fish/ha. Growth of northern pike decreased, in comparison with a growth standard, as early as age 4. Most northern pike were less than age 6, and few fish were older than age 8. Diet of northern pike generally indicated opportunistic feeding strategies with some preference for fusiform prey. Multiple factors were identified as potentially limiting northern pike growth and size structure. Northern pike gro...

Assessment of Seasonal Changes in Energy Density and Condition in Age-0 and Age-1 Muskellunge

Abstract The objectives of this study were to evaluate seasonal changes in the energy density of age-0 and age-1 muskellunge Esox masquinongy and to compare energy density to various estimates of condition. Three treatment groups of muskellunge were evaluated to determine temporal changes in energy density (J/g wet weight [ww]), water content, condition factor (K TL; K = W/L 3, where W = weight and L = total length in centimeters), and relative weight (Wr .; ratio of actual to “standard” weight) through the first year following hatching. Treatment groups were (1) hatchery (muskellunge reared and maintained in hatchery ponds), (2) stocked (hatchery-reared muskellunge stocked in lakes), and (3) natural (muskellunge naturally produced in lakes). Energy levels and relative condition were compared for fish 4 and 11 months old. Differences in energy density were observed between all three treatment groups. An average overwinter reduction of 494 ± 192 J/g ww in energy density was observed over all treatment grou...

Social Aspects of Muskellunge Management in Wisconsin

Abstract Public opinion plays an important part in the successful development of a fisheries management plan. We used a mail questionnaire to survey 1,400 anglers who fish for muskellunge Esox masquinongy in Wisconsin. The survey included defined groups of muskellunge anglers separated by muskellunge club affiliation and geographic location and general anglers selected from a random sample of angler license sales. The survey questions were designed to obtain opinions regarding muskellunge fishery and trophy management in Wisconsin in terms of angling behaviors, regulation options, and perceived problems. All anglers generally preferred fishing with artificial lures and practiced the voluntary live release of legal-length muskellunge. Muskellunge anglers considered a trophy muskellunge to be at least 40 in long, with a preferred length of 50 in or longer. Muskellunge anglers also supported regulations for muskellunge that were based on a waters biological potential, along with increased restrictions on re...

Survival and Cost-Effectiveness of Stocked Fall Fingerling and Spring Yearling Muskellunge in Wisconsin

Abstract Stocking hatchery-reared muskellunge Esox masquinongy is important to Wisconsins muskellunge management program. Typically, large (8–12-in) fingerlings are stocked in fall; however, these fish have poor short-term (30–60-d) survival. To assess survival and cost-effectiveness (maximizing return per dollar invested), both over winter and to age 18 months, I compared success of fish stocked as fall fingerlings (FF) and spring yearlings (SY). Overwinter survival of FF averaged 19% (N = 14; range, 2.7–43.3%). Mortality was highest from stocking through late fall, then declined over winter. In three lakes stocked with both FF and SY, SY survived better (19%) than FF (4%) to age 18 months. Cost analysis based on survival over winter revealed no consistent economic advantage in stocking larger, more expensive fingerlings within the 8–12-in range unless precise information is known about potential predators. Cost comparisons indicated SY were one to four times more cost-effective than FF to age 18 months...

The Influence of Spawning Habitat on Natural Reproduction of Muskellunge in Wisconsin

Abstract Many of Wisconsins 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 som...

Hooking Mortality of Northern Pike Angled through Ice

Abstract Short-term (48-h) hooking mortality was examined for 185 northern pike Esox lucius angled through ice on baited still lines from three Wisconsin lakes. Mortality from capture with size-4 treble hooks baited with live fish was negligible (< 1%); however, mortality associated with pike hooks (also known as Swedish hooks) baited with rainbow smelt Osmerus mordax was substantial (33%). Additionally, mortality was greater for deeply hooked fish, and for fish exposed to short handling times. Pike hooks were associated with a higher percentage of deeply hooked fish than were treble hooks, but hooking location alone did not fully explain the difference in mortality between hook types. Of fish that bled at capture, 84% survived. The length of time that northern pike were allowed to run with the bait plus the time associated with hooking and landing the fish was unrelated to either mortality or hooking location. The use of pike hooks may not be compatible with management of northern pike fisheries if minim...

Muskellunge Scale Interpretation: The Question of Aging Accuracy

Abstract Age and growth data extracted from scales are often used when managing fish populations. However, accurate interpretation of scale annuli in certain species, such as muskellunge Esox masquinongy, has been suspect. The accuracy of age determination was tested with three experienced esocid scale readers who interpreted positive photo images made from acetate slide impressions projected on a microfiche reader. Images were made from scales of 25 known-age muskellunge (3–10 years old) from five Wisconsin lakes. Each scale image was interpreted twice; once with fish length, sex, and date of capture given and once without any information. Of 149 scale interpretations, 32% were assessed with the correct age, 54% underaged, and 14% overaged. The average interpretation deviated from the known age by 1.0 years. Accuracy did not improve when additional fish information was available. General confidence in the interpreters age assessments was low and possibly related to quality of the photo images. Interpret...

Effects of Length Limits on Muskellunge in Bone Lake, Wisconsin

Abstract Minimum length limits are a commonly used management tool for protecting fisheries from exploitation and for improving population size structure. However, little is known about the effects of minimum length limits on populations of muskellunge Esox masquinongy. We monitored changes in the muskellunge population in Bone Lake, a 1,781-acre lake in northwest Wisconsin over a 31-year period (1964–1995) during which time length limits were changed from 30 in to 34 in and from 34 in to 40 in. These changes were compared with population changes in nearby Deer Lake (807 acres), where the length limit remained at the statewide minimum of 32 in. Mean length of adult muskellunge in Bone Lake increased from 31.3 in in 1964 to 36.0 in in 1995. Adult (≥30-in) muskellunge abundance in Bone Lake increased more than five-fold during the study and reached a density of 0.99 fish/acre. Abundance of larger (≥38-in) muskellunge increased 269% following minimum length limit increases between 1982 and 1995. Relative wei...

Density Dependence in Growth and Size Structure of NorthernPike Populations

Abstract The density of northern pike Esox lucius was estimated using mark–recapture techniques and compared with measures of growth and population size structure among 12 north-central Minnesota lakes. The relationships between density and either proportional stock density (PSD, a length-frequency index) or mean back-calculated length were negative and nonlinear. Regression of loge density and PSD explained 63% of the variation in PSD, and regressions of loge density and mean back-calculated length by sex for ages 2–5 explained 47% to 67% of the variation in growth rates among lakes. The relationships remained consistent when data from 17 northern Wisconsin lakes were pooled with those from the 12 Minnesota lakes (although the R 2 was reduced). The fastest growth rates and highest PSDs were observed at northern pike densities of less than 12–14 fish/ha. Inclusion of variables related to the productivity of the lakes only marginally improved the predictive capabilities of the relationship between loge den...

Movement, Habitat Selection, Behavior, and Survival of Stocked Muskellunge

Abstract High poststocking mortality of muskellunge Esox masquinongy has long been an important management problem. This paper documents poststocking dispersal and subsequent movement, habitat selection, behavior, and survival of fall stocked young-of-the-year muskellunge (12.1–13.1 in total length) with the objective of providing insights into the mechanism controlling short-term survival. Radio transmitters were surgically implanted into 27 muskellunge that were then stocked with untagged muskellunge into two northern Wisconsin lakes and monitored for 34 d. Most dispersal from stocking locations occurred within 2 weeks after stocking. Muskellunge selected inshore areas generally less than 10 ft deep. Emersed vegetation, particularly bulrushes Scirpus spp., submersed vegetation, and the trunks and branches of downed trees were preferred cover. The first day following stocking, muskellunge appeared stressed, failing to demonstrate an escape response when approached. Survival of both transmitter-tagged and...