Data from: Historical surveys reveal a long-term decline in muskrat populations

The muskrat (Ondatra zibethicus) is an iconic species in Canada, valued
for both its fur and its integral role in wetland ecosystems, and widely
regarded for its perseverance. However, the resilience of this
semi-aquatic mammal seems to be in question now as increasing evidence
points to widespread population declines. Recent analyses of harvest data
across North America suggest a reduction in their numbers, but this has
not been widely corroborated by population surveys. In this study we
replicated historic muskrat house count surveys at two large Great Lakes
coastal wetlands and present confirmation that declines in muskrat harvest
correspond to actual declines in muskrat abundance. At the Point Pelee
National Park marsh and the Matchedash Bay-Gray Marsh wetland we found
that mean muskrat house counts declined by 93% and 91% respectively
between historic surveys 40-50 years ago and contemporary surveys over the
past seven years. The factors responsible for these dramatic declines
remain unclear but there may be a relationship with changes in the habitat
quality of these wetlands that have occurred over the same time frame. Not
only is the loss of muskrats an issue for the resulting loss of the
wetland ecosystem services they provide, but it may be an indication of
broader marsh ecosystem degradation. As such, a scarcity of muskrats
should be considered a red flag for the state of biodiversity in our
wetlands. Continued surveys and ongoing research are needed to shed more
light on the current status of muskrat populations and their marsh
habitats across their native range.