Restricted Summer Habitat and Growth of Northern Pike in Two Southern Ohio Impoundments

Available summer habitat for northern pike Esox lucius in southern Ohio impoundments is restricted by warm epilimnetic temperatures and anoxic bottom waters. We used temperature-sensitive radio transmitters to determine locations of adult northern pike in two impoundments, and we related seasonal growth of other tagged fish to availability of suitable habitat. We implanted transmitters in eight fish in one lake and nine fish in the other; fish locations were monitored from April to October. Condition factors were highest in spring and lowest in late summer. Individually tagged fish lost weight during summer. At the onset of summer thermal stratification, fish moved from inshore to offshore locations that were frequently associated with macrophytes or bottom structures such as submerged stream channels. When lake surface temperatures exceeded 25°C, fish were found in the coolest available water with dissolved oxygen concentrations of at least 3.0 mg/L, and they were restricted to this stratum for 2–3 months. Although northern pike lost weight during the period of habitat constriction, their annual growth exceeded the average for the species.