Variation in an Annual Movement Cycle of Flathead Catfish within and between Two Missouri Watersheds

Flathead catfish from the main stems of the Grand River and Cuivre River were implanted with 400‐d radio transmitters to determine an annual movement cycle. Substantial variation was observed within and between watersheds. Flathead catfish displayed annual movement that consisted of three main periods punctuated by brief migrations. The first, a period of overwintering was followed by migration from wintering areas in early spring, followed in turn by the prespawn/spawning period, which is characterized by increased activity, including longer movements (up to 187.6 km) during spates. After another short migration period came a third period of postspawn summer/fall restricted movement, which was followed by fall migration back to overwintering areas. Within this framework, individual fish displayed at least three variations of this annual pattern. Some individuals entered Grand River and Cuivre River watersheds during the prespawn/spawning period only, returning to the Missouri River or the Mississippi River during summer/fall, overwintering there, and reentering the tributary the following spring. Other individuals entered tributary watersheds for the prespawn/spawning period and remained there for the summer/fall period, returning to the big rivers to overwinter. In the Grand River, all individuals moved downstream (9–45 km) to the Missouri River and overwintered. Finally, some individuals in Cuivre River remained throughout the year, migrating short distances within the river to spawn, feed, and overwinter. The finding that fish were harvested at locations tens of kilometers from the areas where they spent considerable time suggests a larger scale for management than has previously been proposed.