A new paper demonstrates that small-scale flood-control structures, called floodgates, transform streams from nurseries for salmon and native species to hotspots for invasive species. The project examined creeks that flow into large rivers in the Lower Fraser region.

 

This research was led by David Scott and performed as part of his Masters project in the lab of Jonathan Moore at Simon Fraser University. It was published in the Canadian Journal of Fisheres and Aquatic Sciences. 

 

What are floodgates?

Floodgates are basically reverse dams that keep high tides and high flows from going upstream through culverts and dikes and flooding habitat. They are globally common but their impacts are not as well-studied as their bigger counterparts, dams. 

 

There are approximately 500 floodgates in the lower Fraser River region. 

 

 

From nurseries to hotpots for invasive species

The researchers compared streams with and without floodgates. Streams with floodgates had: 

• 2.5 times fewer young salmon

• 3.1 times more invasive fish

 

Dead zones

Recent research led by (former) undergraduates Jen Gordon and Michael Arbeider in the same group also discovered that floogates were associated with hypoxic zones with levels of dissolved oxygen that were well lower than needed for protection of aquatic life. 

 

So what? 

Given that there are hundreds of floodgates in the lower Fraser River region, their cumulative effects on fish populations may be large. 

 

There are opportunites to restore floodgates so that they not only provide flood protection but also are fish friendly. 

 

Watershed Watch Salmon Society (link), in partnership with other groups, is calling for CONNECTED WATERS.