Population characteristics and habitat selection of muskrats (Ondatra zibethicus) in response to water level management at the Summerberry Marsh Complex, The Pas, Manitoba, Canada

Abstract

<p>Hydroelectric developments have significantly altered the hydrology and the historical wetland cycle in the Saskatchewan River Delta (SRD) by reducing both long term and within year flood frequency. This research details the responses of SRD wetlands to water level manipulation and links it to the habitats selected by muskrats thus highlighting the conditions that should be the focus of wetland management. Following the partial drawdown (PD) in the fall of 2007, muskrat densities derived from mark recapture surveys did not differ between PD and full supply level (FSL) wetlands. On a per flooded area basis, PD wetlands supported residual muskrat population at similar densities as FSL wetlands during the years of the drawdown. The partial drawdown resulted in increased amounts of senescent vegetation in PD wetlands in 2008 and 2009, mainly affecting Carex and Typha vegetation classes. The result of habitat selection modeling was generally consistent with other studies of muskrats, although it was complicated by the habitat structure of these northern wetlands. Muskrats selected for rooted Typha with greater frequency than any other habitat, followed by rooted Equisetum. Ducks Unlimited Canada's records from 1979 to 1990 show that water level drawdowns were successful at increasing muskrat house densities in SRD wetlands. In the years after a drawdown muskrat house densities generally increased and peaked three years after a drawdown, however the ten year densities were unaffected. Low muskrat densities, and low recruitment in SMC wetlands compared to other northern deltas are likely due to degenerating wetland habitat conditions created by prolonged water level stabilization. Small scale water level manipulation efforts by various managers, most notably Ducks Unlimited Canada, have produced increases in muskrat populations. Although expensive and logistically difficult the results I have presented suggest that a large scale drawdown and refill would stimulate muskrat populations in the SRD.</p>