Historical surveys reveal a long‐term decline in muskrat populations

Abstract

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 semiaquatic 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 yrs ago and contemporary surveys over the past 7 yrs. 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.

Zooarchaeological assemblages contextualize the historical ecology and harvest of fur-bearing mammals in Vermont

“…However, examination of historical Fur Trade records suggest that recent perceptions of overpopulation are a result of shifting baselines, as use of an 1850, rather than, 1970, baseline results in a reversal of trends from apparent increase to actual decline (Collins et al, 2020). Some harvest estimates within the last few decades similarly suggest muskrats are declining across their range in Canada (Sadowski and Bowman, 2021) and the northeastern United States (Roberts and Crimmins, 2010), potentially linked to disease.…”

Assessment of heavy metal and metalloid concentrations at Horicon National Wildlife Refuge

“…However, wetlands also support a large number of trophic levels, which makes higher organisms susceptible to toxicological effects resulting from biomagni cation (Ali & Khan, 2019). One such species that may be at risk is the muskrat (Ondatra zibethicus), a common, primarily herbivorous, semi-aquatic mammal that is declining across North America for undetermined reasons (Sadowski & Bowman, 2021). One potential contributing factor is contaminants including heavy metals and metalloids, which may be introduced to their diet through the ingestion of cattail roots (Erickson & Lindzey, 1983).…”

The use of orthoimagery and stereoscopic aerial imagery to identify muskrat (Ondatra zibethicus) houses

“…Harvest declined in the southeastern United States by >90% between 1970 and 2012 (Ahlers and Heske 2017), and harvest in the northeastern United States and eastern Canada declined 75% between 1986and 2006(Roberts and Crimmins 2010. In 2 coastal wetlands in Ontario, Canada, the number of muskrat houses has declined >90% in recent decades, and muskrat harvest throughout the province has declined by 90% since the 1980s (Sadowski and Bowman 2021). In Prince Edward Island, where declines have been observed by trappers, one wetland experienced a 6-fold decrease in density since the 1960s (Gregory et al 2019).…”

“…The use of muskrat sign can be unreliable and provide limited information compared to other methods (Boutin and Birkenholz 1999). House counts are the most popular survey method for muskrats and can be completed during the winter by snowmobile, ski, or walking transects on the frozen wetland, or in the spring or summer by canoe or walking transects (Dozier 1948, Proulx and Gilbert 1984, Thurber et al 1991, Greenhorn et al 2017, Sadowski and Bowman 2021). However, house counts can also be labor intensive, time consuming, and logistically challenging when conducted from the ground due to potential challenges in accessing the wetland of interest (e.g., remote location, lack of landowner permission) and the physical obstacles that may be encountered within the wetland (e.g., deep snow, thin ice, dense vegetation).…”