Making Cootes a paradise again
A history of carp and invasive plants have all contributed to the decline of this wetland area in Ontario. Now, restoration efforts are under way.
Thursday, July 25, 2013 - 13:18
Photo: Katherine Bailey
A couple of weeks ago, the research crew for Great Lakes Coastal Wetlands Research explored the marshes and large wetland of Cootes Paradise in Ontario, Canada. As a member of this small, six-person crew, I was able to experience the thrill of boating across a large wetland that is home to a large population of mute swans, painted turtles, northern pike, yellow perch, rainbow trout, and scores of other freshwater fish. However, despite the superficial beauty of the wetland, human development and farming in the watershed has degraded the marsh’s aquatic plant cover to 15 percent of its original pristine quality. Many factors over the years played major roles in the decline of native plant species; introduction of invasive plant species such as purple loosestrife, phragmites, and reed manna grass, and the introduction of the Asian carp in 1831, have all contributed to the health decline of this marsh.
Why are wetlands, and marshes in particular, so vital in the first place?
In a pristine or minimally impacted marsh community, a diverse community of plants serves as the basis for a healthy array of wetland vegetation. Similar to estuaries, marshes have a high rate of primary productivity, which provides necessary food and habitat to birds, mammals, fish, invertebrates and reptiles. Native species of cattails provide stability in muddy banks of marshes and also buffer against high winds and wave action. Marshes have a special role as a nursery for fish such as bass, perch, pike, and minnows in the warm shallow waters. Cootes Paradise is very special because it is the largest wetland on the western shore of Lake Ontario.
Enter the carp
A close cousin of the common goldfish, Asian carp (Cyprinus carpio) have wrought havoc on plant communities in Cootes Paradise because of their abusive behavior toward native plant species in the marsh. In the 1930s, the loss of wild rice and wild celery in Cootes Paradise was attributed to carp activity; the roots of aquatic plants are where their favorite food are located, and as a consequence, damage to these plants can destroy their ecological function. Often carp will uproot plants, which ultimately kills the least resistant types, and this loss can lead to the loss of stream channels in the marsh. Just when you thought uprooting plants was enough of a bad thing, carp do even more harm in the manner in which they feed. As bottom-feeders, they forage on the bottom of marsh banks by siphoning a bunch of muck and organic debris. Then, after they consume the desired food particles, and expel the remaining debris. This muddies the water and increases turbidity, which minimizes the amount of sunlight that can reach beyond the photic zone in the marsh; thus, diversity of plant growth of submergent plants is diminished.
When considering how devastating carp are to Cootes Paradise, it seems ironic that in the late 1800s carp were regarded as a “worthwhile addition to the natural fauna of North America.” This has definitely turned out to not be the case!
Despite the damaging effects on aquatic plants, remedial action has been taken and has shown to be effective. The Royal Botanical Gardens initiated Project Paradise in 1991 to restore Cootes Paradise marsh through methods such as wetland planting inside carp exclosures. From 1996 to 1997, the fishway on the Desjardins Canal between Hamilton Harbour and Cootes Paradise was constructed to prevent the spring migration of adult carp from Hamilton Harbour into the marsh. Simultaneously, the grates on the fishway maintain water flow and access for smaller fish. Since its construction, the fishway has succeeded in minimizing the adult carp populations within the marsh, from 50,000 carp prior to 1997 to between 2,000 and 3,000 carp after the Fishway was constructed. This is a huge milestone in laying the foundation for restoring the integrity of the wetland. Together with the sorting of fish along the fishway and monitoring efforts of coastal wetlands, ecological restoration is indeed possible.
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