Rodney B. Pierce

Exploitation of Northern Pike in Seven Small North-Central Minnesota Lakes

Abstract Exploitation of native northern pike Esox lucius was studied in seven small ( 500 mm total length) were approximately 2 to 9 times greater than for smaller fish (≤500 mm). Relatively high total annual mortality rates (mean = 0.48) compared to annual exploitation ...

An Overview of Northern Pike Regulations in North America

Abstract Northern pike (Esox lucius) is a popular sport fish in the United States and Canada that is currently managed for multiple angler uses. However, there has been increased concern over lower quality (i.e., smaller fish) northern pike populations. In 1997, the Esocid Technical Committee (ETC) of the North Central Division of the American Fisheries Society surveyed natural resource agencies about their northern pike management. In addition, a round-table discussion on the quality of northern pike management was conducted in 1999. This paper is a summary of the ETC findings. In some cases, northern pike regulations have existed since the late 1800s, but most states and provinces did not use regulations until the 1950s or 1960s. Some agencies currently manage northern pike for angling quality (i.e., more large fish), others have few or no northern pike regulations, and some agencies manage for quality in some water bodies and do not manage northern pike at all in other water bodies. In general, states ...

Hooking Mortality of Walleyes Caught on Live and Artificial Baits

Abstract The potential benefits of catch and release or protective size limits in recreational fisheries for walleye Stizostedion vitreum can only be realized if released fish survive. In this study, hooking mortality rates were determined for adult walleyes caught on leeches and artificial lures in two Minnesota ponds. The mortality of walleyes caught and released by anglers in Klawitters Pond was 5%, though confidence intervals indicated that hooking mortality could have been as high as 23%. Mortality of walleyes caught on leeches (10%) was higher than mortality for walleyes caught on artificial lures (0%). An estimate of hooking mortality in Clubhouse Pond, unadjusted for natural mortality, was 16%. Walleyes caught on artificial lures were hooked primarily in the lips, whereas fish caught with leeches tended to be hooked more deeply in the throat and gut. Walleyes caught on leeches were smaller than those caught with artificial lures and were more likely to be males. Catch rates were similar for live ...

Angler Noncompliance with Slot Length Limits for Northern Pike in Five Small Minnesota Lakes

Abstract Successful application of special regulations, such as slot length limits for northern pike Esox lucius, hinges upon angler compliance with the regulations. Yet, noncompliance was greater than expected under 508–762-mm (two lakes) or 559–762-mm (three lakes) protected slot length ranges in five north-central Minnesota lakes. Illegal fish averaged 13% of the harvested northern pike measured by creel clerks and 19% of the tag returns. Exploitation of similar-sized northern pike was greater in two reference lakes that had no size limits. In reference lakes, an average of 57% of creeled fish and 70% of tag returns were fish of sizes that would have been protected by slot length limits. In spite of extensive promotional efforts, the high (up to 29% on one lake) voluntary tag returns from illegal-size fish implies a simple lack of awareness of special regulations among anglers. Levels of noncompliance reported here show that individual lake management will require a fishing public that is more aware of...

The Relationship of Bluegill Growth, Lake Morphometry, and Water Quality in Minnesota

Abstract We evaluated the relationships between the growth rate of bluegill Lepomis macrochirus and lake morphometry and water quality at 1,146 Minnesota lakes to determine the potential strength of the latter two variables in a model of bluegill growth. Secchi depth and maximum depth were negatively correlated with bluegill length at ages 1–6, whereas total alkalinity, percent of littoral area, and mean maximum July air temperature were positively correlated with bluegill length at those ages. Secchi depth, maximum depth, and total alkalinity explained 16–33% of the variation in the growth of bluegill through their first 5 years. The lake morphometry and water quality variables did not explain more of the variation in bluegill growth among lakes because other variables, such as food resources, species interactions, and exploitation also affect bluegill growth. However, these two variables can be used to preliminarily sort candidate lakes for regulation of recreational angling for bluegill and should be c...

Variable Catchability and Bias in Population Estimates for Northern Pike

Abstract The magnitude of biases introduced into population estimates by the varying catchability of fish was observed by employing several strategies for estimating population sizes of northern pike Esox lucius in six north-central Minnesota lakes. The strategies relied on commonly used sampling techniques for northern pike and differed in the degree to which they addressed differences in catchability among fish. Biases were measured as percent differences among population estimates. Estimates of known populations of tagged fish showed that the Petersen technique, which incorporated independent gear types for marking and recapture, was relatively unbiased. Biases from differences in catchability due to fish size were small. In contrast, large biases from differing fish behaviors and habitat uses were found in removal or multiple mark–recapture methods. Both method types relied on sampling nearshore movements of northern pike during early spring, and both severely underestimated population sizes. Removal ...

Bluegill Recruitment, Growth, Population Size Structure, and Associated Factors in Minnesota Lakes

Abstract To better understand the differences among populations of bluegill Lepomis macrochirus, we analyzed the relationships between bluegill recruitment, growth, population size structure, and associated factors from approximately 2,600 Minnesota lakes. Potential explanatory variables for our models included bluegill year-class strength, growth, population size structure, the relative abundance and mean weight of predator species, physical and chemical characteristics of lakes, summer air temperature, and season. Bluegill year-class strength, growth, and population size structure were more strongly related to each other than to predator and lake characteristics, temperature, or season. Growth of age-6 bluegills was positively associated with population size structure and inversely related to year-class strength, suggesting density-dependent growth effects for adult bluegills. Growth of age-3 bluegills was inversely related to Secchi depth, so early growth and productivity may be linked. Bluegill popula...

Management Briefs: Tag Loss and Handling Mortality for Northern Pike Marked with Plastic Anchor Tags

Abstract Two assumptions of mark-recapture experiments are that marks are not lost and that mortality does not differ between marked and unmarked fish. To evaluate if these assumptions were met on northern pike Esox lucius marked with plastic anchor tags, we estimated tag loss from and handling mortality of northern pike trapped and tagged during the spring in a lake in Minnesota. Annual tag loss was 1.8% for Floy tags and 0% for modified Dennison tags. Proportions of tags observed to have been lost from creeled fish in six other lakes in Minnesota were 1.2% for Floy tags and 2.5% for Dennison tags. Short-term handling mortality of northern pike trapped, tagged, and held in net pens was 2.4%.

Effectiveness of Liberalized Bag Limits as Management Tools for Altering Northern Pike Population Size Structure

Abstract Management efforts to restructure populations of northern pike Esox lucius consisting of small (<60 cm total length), abundant individuals in small (<200 hectares) Minnesota lakes has focused on removal by trap-netting and promoting angler harvest through liberalized bag limits. Removal by intensive trap-netting was demonstrated to be ineffective in altering northern pike population size structure, and anglers harvested substantially fewer fish than were removed by trap-netting. Unless more anglers begin harvesting more small northern pike, liberalized bag limits hold little promise as a management tool for altering northern pike population size structure in small Minnesota lakes.

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...