Coastal Wetlands Connected to Lake Ontario Have Reduced Muskrat (Ondatra zibethicus) Abundance

Abstract

Low muskrat (Ondatra zibethicus) abundance has been linked to suboptimal water levels, predation, and changes in vegetation composition. We surveyed 43 coastal Lake Ontario wetlands for muskrat houses during winter 2014, and compared zero-inflated Poisson (ZIP) regression models to evaluate effects of wetland and surrounding landscape characteristics on the presence and abundance of muskrat houses. The most informative models were those indicating whether the wetland had an open connection to Lake Ontario. Connection to the lake, which exposed wetlands to the water regulation regime of the Lake Ontario-St. Lawrence River system, had a negative influence on muskrat house abundance. Muskrats appeared to be absent from 56% of the surveyed wetlands, and houses occurred at a mean density of 0.27 houses/ha, which was lower than the mean density observed in previous studies. Mean muskrat house density was higher in wetlands without a connection to Lake Ontario (1.04 houses/ha), and muskrats were more prevalent in these wetlands (78%). The apparent low abundance of muskrats in the Lake Ontario study area is concerning, since muskrats are commonly recognized as “ecosystem engineers”, and consequently, the loss of muskrats has the potential to affect both the biotic and the abiotic wetland characteristics.