Salmon live interesting lives: they are born in fresh water, then migrate to the ocean, where they grow to maturity, returning back to fresh water to breed, sometimes hundreds of kilometres, navigating obstacles along the way -- including swimming up waterfalls. And not just any freshwater will do, either: salmon return to the very spot they were born to lay their own spawn.
Artificial water constructions -- such as dams -- can therefore pose a serious problem. Fish can become disoriented, or get injured or killed due to turbines or spillways, and their travel times can get longer due to the disruption of natural water flow. One solution is the fish ladder, a structure that is designed to help migratory fish negotiate the changed waterways.
Or you could just fire them through a cannon.
Thus the salmon cannon was born -- the invention of a Whooshh Innovations, a company who had developed a method of gently and quickly transporting fruit over long distances via a tube. When the team discovered that hydroelectric dams were causing migrating salmon significant difficulties, they decided to adapt the tube to fish.
It works a little like a pneumatic tube. Fish go in one end, and the soft fabric of the tube forms a seal around the body of the fish, creating a vacuum, which in turn propels the fish through the tube at a speed of around 5 metres to 10 metres per second (11 mph to 22 mph).
In this way, the fish can be transported gently and easily to a new location, out of the water for just a few seconds until they land safely in the water at the other side. So far, the team has tested the system at Kalama Falls, Columbia River Gorge and Roza Dam in Washington state, where they have both manually fed fish into the tube and let the fish swim into it themselves -- which, the team said, they seem quite happy to do.
There's something magnificently slapstick about it -- but, according to Whooshh -- it could provide cheap, safe, fast transport for fish, both in fisheries and in the wild.