The Neosho Madtom and the Multifaceted Nature of Population Limiting Factors
Mark L. Wildhaber
Abstract.—The Neosho madtom Noturus placidus is a small ictalurid formally recognized as a species in 1969 and federally listed as threatened in 1990. What is presented here is an in-depth review of research done on Neosho madtom since it was listed as threatened. The overall goal is to directly address questions put forth in the original recovery plan. Information presented provides a basis for updating the status of and current recovery plan for the Neosho madtom along with guidance as to additional research needed for Neosho madtom recovery efforts to be successful. Currently, Neosho madtoms are found in main stems of the Neosho, Cottonwood, and Spring rivers in Kansas, Missouri, and Oklahoma. These three rivers have been altered by reservoirs, heavy metals contamination, and gravel mining. Effects of these factors were identified as areas of information needed for recovery of the species, along with a better understanding of its reproductive biology and overall ecology. Since the initial recovery plan was written, numerous research efforts have and continue to address these questions through collaborative studies involving a partnership among federal and state agencies, private landowners, and universities. Within the Spring River, Neosho madtom populations are limited by poor habitat quality in the upper section (i.e., upstream of Center Creek) and by heavy metals contamination in the lower. In the Neosho River system, the decrease in Neosho madtom densities downstream of John Redmond Reservoir seems to be related to decreased turbidity and coarser substrate. Other benthic fishes found with the Neosho madtom, such as the channel catfish Ictalurus punctatus, have shown a similar change in density. Neosho mad-tom population declines also have been linked to low-head dams, which result in decreased flow and increased siltation upstream and coarsening of substrate downstream. Furthermore, Neosho madtom reproductive behavior has been shown to be related to environmental cues such as photoperiod, temperature, and water velocity, thereby indicating potential for reservoir release patterns to disrupt reproduction through changes in flow. Research has shown that Neosho madtom populations are limited by different factors in different parts of the species’ geographic range. Additional research is needed on Neosho madtom movement rates among gravel bars, population genetics, aging methods, age distribution within wild populations, growth rates, population viability, effects of predation, and sensitivity to environmental contaminants.