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 growth was negatively related to northern pike density, water transparency (Secchi depth), and abundance of small bluegills. Extensive littoral areas, water temperatures greater than 21°C during the growing season, and winterkill also limit northern pike growth and size structure. Effective management of these small lakes will probably require an individual-lake approach to identify specific mechanisms limiting growth.