Movement and Site Fidelity of Flathead Catfish in the Minnesota River
Steven M. Shroyer
Abstract.—The flathead catfish Pylodictis olivaris is one of the most important game fishes in the lower Minnesota River, providing a high-quality angling fishery. Information on flathead catfish movements and site fidelity in the Minnesota River at the reach scale is needed before fisheries managers consider options such as reach-specific fishing regulations. In addition, this information is necessary to determine if estimates of population abundance are feasible and what study design is most appropriate. Therefore, 18 radio- and acoustic-tagged adult flathead catfish were manually located in the lower Minnesota River during late summer and fall in 2008 and 2009. Most fish remained within about 2 km of their capture locations during daylight hours in August–September 2008. However, 17% of the fish emigrated from the 9.3-km study reach before the end of September, and all emigrated by the end of October. Fourteen (78%) of the original 18 fish survived and were present in the study reach again during August–September 2009. High site fidelity could result in heterogeneous vulnerability to late-summer angling among river reaches if some individual fish consistently return to areas frequented by anglers and others return to more remote and relatively inaccessible areas. Due to high survival and late-summer site fidelity, the potential exists for high recapture probabilities with repeated late-summer mark–recapture sampling in the same study reach; however, there is evidence that temporary emigration could be an important issue in long-term studies.