The Fraser River stretches from Blackrock Mountain in the Rocky Mountains on the British Columbia and Alberta border. It flows for 1,375 kilometres before it comes to an end in the Straight of Georgia. It’s ending, the Fraser River Delta, culminates in the most important habitat for fish and birds on the west coast of Canada.
It faces numerous threats to its survival. Development in the region threatens migratory birds dependent on the estuary for their critical food sources that burrow in the mudflats and salt marshes.
The population of the endangered Southern resident killer whale is under siege as its food sources dwindle. Commercial fishing faces closures as Chinook stocks plummet.
Along the banks on the Fraser River Delta, another threat grows at an alarming rate. Invasive cattails are choking out was once critical habitat that helped salmon stocks thrive in their early stages.
Invasive species cattail management experiment underway at Frenchies Island
DUC is working with Dan Stewart, a recent master’s graduate at the University of British Columbia, on an invasive cattail management experiment on Frenchies Island in the South Arm Marshes Wildlife Management Area.
For the past three years, crews set out to cut down the invasive plant across the island in hopes of finding a solution to manage the removal of the plant best as it overtakes habitat across the Fraser River Delta. Located in Delta, B.C., the experiment focuses on removing cattail by various methods to allow the island to become better suited for salmon and waterfowl habitat.
Stewart said when the site was excavated a decade ago, it had a series of channels designed for juvenile salmonids and open water habitat for waterfowl.
“Unfortunately, over time, the cattail encroached in these channels, essentially reducing their value for these target species,” says Stewart.
Invasive cattail remove is critical to biodiversity in the South Arm Marshes
The removal of cattail is critical to the area, as the South Arm Marshes supports the highest densities of waterbirds and shorebirds in Canada.
This experiment is critical from DUC’s perspective as more waterfowl winter in this area than Canada combined. Estimates put as many as 1.4 million birds relying on this habitat annually.
The South Arm Marshes Wildlife Management Area is an internationally designated Western Hemisphere Shorebird Reserve Network site.
The area is known to see a diverse range of migratory waterfowl, including green-winged teal, northern pintail, goldeneye, wigeon, ruddy duck, and snow geese. The channels of Frenchies Island, and other habitats across the South Arm Marshes, offer vital habitats for nearshore and freshwater fish species. Young chinook, chum, pink, spring, and chum rely on the tidal marsh and channels in their early stages of life.
As a result, the amount of open water habitat and fish channel habitat has essentially been restored to its original condition. Crews have already seen an increase in waterfowl usage in these open water areas, including foraging great blue herons.
Promising signs emerge following removal effort
Stewart says they observed positive signs of native plants taking hold in places formerly with stands of invasive cattail.
Native plants like Lyngbye’s sedge are taking root once again, said Stewart. He also identified American water plantain, water parsnip, and wapato, a culturally important species for Indigenous Peoples.
“After the cattail cutting, channels on the island that had been filled with the plant are now opening back up, allowing greater water flow, which benefits both waterfowl and fish,” notes Stewart.
He says the positive signs of the project have led to a third season of cutting on the island.
While the cutting at Frenchies has, to this point, not led to wide-scale removal, there is a reason for optimism.
Stewart says there is evidence that their energy reserves (below ground rhizomes) are declining across the site, suggesting the cutting is exhausting the cattail. He says cutting in the low elevation portions of the marsh, like in the channels, has been highly effective, with nearly 100 per cent eradication.
“As a result, the amount of open water habitat and fish channel habitat has essentially been restored to its original condition,” said Stewart. “Crews have already seen an increase in waterfowl usage in these open water areas, including foraging great blue herons.”