Lampricide Exposure in Mudpuppies (Necturus maculosus): Comparing Demographic Responses

Since 1958, the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) has been periodically used in nursery streams of the Great Lakes Region to control the invasive Sea Lamprey (Petromyzon marinus). Some treatments of streams containing Common Mudpuppies (Necturus maculosus), a species of large-bodied fully aquatic salamander found throughout the Great Lakes Region, have resulted in large amounts of mudpuppy mortality. However, the long-term consequences of mudpuppy mortality are not well understood. Following a TFM application in 1986, the mudpuppy population experienced an estimated 29% decline in the Grand River, Ohio. Since then, the Grand River has continued to be treated with TFM every three to five years. Mudpuppy population estimates suggest a slow to moderate decline over the last 32 years. In 2021 and 2022, we returned to the Grand River to estimate mudpuppy population size, survival, growth rates, and population demographics using mark–recapture methods. Following our first year of mark–recapture surveys, the US Fish and Wildlife Service treated the Grand River with TFM in April 2022. Despite observed mudpuppy mortality in the Grand River following TFM treatment, our population and survival estimates did not indicate decline following the 2022 TFM treatment. We also conducted a mark–recapture study at Alum Creek, a river that has never been treated with TFM. While differences in habitat and survey methods preclude direct comparison of the sites, we found little difference in population size or survival between sites. However, individual growth rates suggest that Grand River mudpuppies may reach sexual maturity at a younger age and attain a smaller adult size, patterns consistent with an exploited population. Smaller adults could have reduced fecundity, be more susceptible to predation, and have lower competitive ability, which may have consequences for long-term population persistence. Our study highlights the need for future studies to compare treated and untreated tributaries in the Great Lakes to address lingering concerns and long-term effects of TFM treatments.