Thermal Habitat of Large Versus Small Northern Pike in Minnesota Lakes

We quantified thermal habitat used by northern pike in two north-central Minnesota lakes where a wide range of water temperatures were available during summer.  Temperatures and depths of large and small northern pike were monitored and compared year-round using ultrasonic telemetry and fixed-station hydrophones.  Northern pike use of the various temperatures and depths was highly individualistic, but nevertheless illustrated important seasonal behaviors.  Modeling of behavior patterns within each month often showed an interaction between the sizes of northern pike and their diel movements.  Selection ratios developed from measurements of available thermal habitat indicated that thermal preferences of the northern pike varied somewhat between lakes during the warmest month of the summer (August).  However, preferred temperatures for large northern pike were typically 16-21C.  This work has important implications for sampling northern pike, for proposing and evaluating sport fishing regulations designed to promote larger northern pike, and for managing the species in the face of climate change.