The Cow River system, in Monticello, is a prime example of the dramatic impacts of beavers on a pristine river. Historically, Cow River was known to feature strong populations of Atlantic Salmon, as well as healthy stocks of Brook Trout. Blessed with cool waters and gravel stream beds, this system was a haven for fish and a picture of natural splendour. In recent years, however, the expansion of beavers into the area has caused a significant decline in the quality of fish habitat in the Cow River system. Specifically, the countless dams constructed by beavers impede fish passage and obstruct stream flow.

While working on this river, the Souris River Watershed stream enhancement crew encountered many dams of this stature. The waters contained behind these dams become stagnant, a state that leads to elevated water temperatures and decreased oxygen levels. Such conditions are not conducive to fish survival and success, and the river has suffered greatly because of it. These large dams also effectively eliminate any possibility of sea-run trout and salmon from accessing suitable spawning habitat in the upstream sections. This denies the river of the opportunity to replenish its fish stocks, resulting in a steady decline in populations in recent years. As evidence to this fact, sampling performed recently on this river yielded alarmingly low numbers of brook trout and salmon.

Beavers have also negatively affected the Cow River system in other ways. To sustain itself, beaver colonies rely on alders as their primary food source. To facilitate the growth of this early successional species, beavers will cut down larger trees to increase light penetration in an area. Habitat alteration is striking, with mature woodlands transformed into muddy, alder ridden meadows.

www.flickr.com Souris & Area Branch PEI Wildlife Federation's Cow River Project photoset View a series of photos of the work conducted in 2007.

The most disheartening reality of beaver expansion is that once an area has been abandoned by the colony, the effects are felt for many years afterward. In flat lands, such as Cow River, the massive dams and lodges still persist until manually removed. Removal of beaver dams requires a great deal of effort from a large crew of enhancement workers. This consumes time, equipment, and a large amount of our organization's budget, resources that could be better allocated in other areas. Unfortunately, if the beavers are still present in an area, they will rebuild their dams within days, making most removal efforts futile. Such a cycle is one of the most pressing issues that the Souris and Area Branch is confronted with on an annual basis. Beavers, as a wildlife species on Prince Edward Island, certainly deserve to live and prosper in specific habitats in our area. However, certain river systems are so important that they cannot afford to be adversely effected by a beaver colony. Cow River is one such system, and this problem will require close monitoring and our continued attention.

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Souris Branch of the P.E.I. Wildlife Federation

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