Just a couple of hundred of years ago, the estuaries around Metro Vancouver were filled with fallen trees and other large woody debris that had drifted down from upstream headwaters. Large woody debris gave young salmon adapting to salt water conditions cover from their predators and helped in the establishment of healthy intertidal vegetation. It also added structural complexity to the fish habitat: creating riffles, pools and crannies with different water conditions. Without this, their habitat becomes very uniform – just a straight flowing stream. Think of a neighborhood filled with only one bedroom apartments or a food court that only sold pizza. It doesn’t give young fish a lot of options.
But when humans started to develop these waterfront habitats for industrial and residential uses, we removed all this wood. It just got in our way. The estuaries were transformed into not much more than large ditches, seriously degrading fish habitat.
Now, humans are looking to restore these habitats by bringing back the wood. Large woody debris structures (kind of like small log jams) are installed into the estuary stream bed by securing them to boulders using cable and epoxy cements. Echo Ecological describes the process on their website. No, not exactly natural, but large logs can’t be allowed to drift around waterways that are used heavily for commercial shipping and recreational boating.
It could take a few years to see improvement, but with more work like this, we just might see more young salmon heading out to the open ocean from Vancouver’s estuaries and, even better, returning in larger numbers to spawn new generations.
photo: Julie Porter, watergoddess.ca