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Abstract
We monitored depths and temperatures used by large (>71-cm) versus small Northern Pike Esox lucius in three north-central Minnesota lakes with either acoustic telemetry or archival tags. Individual Northern Pike demonstrated flexibility in depths used within a season and between years. The fish had some tolerance for low levels of dissolved oxygen (<3 mg/L), but depth selection was generally constrained by low dissolved oxygen in summer and winter. The fish more fully exploited all available depths during winter and thermal turnover periods. During July and August, large Northern Pike tended to follow the thermocline into cooler water as upper water layers warmed. Selection ratios indicated that large Northern Pike preferred water temperatures of 16–21°C during August when temperatures up to 28°C were available. In two lakes providing dense overhead cover from water lilies in shallow water, small Northern Pike used warmer, shallower water compared with large fish during summer. In a third lake providing no such cover, small fish were more often in deeper, cooler water. For small Northern Pike, temperature seemed to be a secondary habitat consideration behind the presence of shallow vegetated cover. This study provided detailed temperature selection information that will be useful when considering temperature as an ecological resource for different sizes of Northern Pike.
Received March 27, 2013; accepted June 27, 2013
ACKNOWLEDGMENTS
We thank Beth Holbrook, Melissa Drake, Don Pereira, two anonymous reviewers, and the journal's editorial staff for improving the manuscript. This study was funded in part by the Federal Aid in Sport Fish Restoration (Dingell–Johnson) Program (D-J Project F26-R, Study 685, Minnesota), and more detailed data from this study will be published in a Minnesota Department of Natural Resources Fisheries Investigational Report. Reference to trade names does not imply endorsement by the U.S. Government.
