Abstracts

Presented by Dale Wrubleski - Email: d_wrubleski@ducks.ca

Delta Marsh is an important mid-continent waterfowl staging area in Manitoba. However, the marsh has been degraded by an artificially regulated water regime, eutrophication and invasive species, all of which have contributed to declining waterfowl numbers. A multi-agency partnership has embarked on a restoration project to address factors contributing to the deterioration of the marsh. The first phase of the restoration project consists of partial exclusion of an invasive fish species, common carp (Cyprinus carpio), which overwinter in Lake Manitoba but use the marsh as spawning and feeding habitat. Experimental field studies demonstrated that common carp contributed to habitat changes observed in the marsh, including increased turbidity, phytoplankton blooms and loss of submersed vegetation. During the winter of 2012-2013, exclusion structures were constructed on channels connecting the marsh to the lake. These structures restrict large common carp (> 70 mm maximum body width) access to the marsh. A ten-year research program (pre- and post-carp exclusion; 2009 to 2018) assessed the impacts of common carp exclusion on the marsh. In survey transects in the east unit of the marsh, the area of submersed aquatic vegetation increased sevenfold (37 ha to 267 ha) between 2009 and 2018. Northern watermilfoil (Myriophyllum sibiricum) initially dominated the submersed plant community response but sago pondweed (Stuckenia pectinata) has also increased. The waterfowl response has been positive fall staging canvasback and scaup densities have increased 20 and four times, respectively, from the decade prior to common carp exclusion, and are the highest numbers recorded since the 1960-1980s.