Fish in Tubes
The salmon cannon is just one place where fish go tubular.
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Behold the salmon cannon—developed to help salmon traverse dams; made famous by the comedian John Oliver. Recently, the cannon’s creators suggested that officials in the state of Washington should use the cannon to boost salmon over dams so that the fish can spawn, ultimately creating more food for hungry and endangered southern resident killer whales. Firing live fish through the air may be rich fodder for late-night television, but there are a surprising number of situations where salmon and other fish sluice through tubes.
The Access Ramp
Before there were cannons, there were ladders. Fish ladders help salmon over obstacles like large river-blocking dams just as switchbacks help cars climb steep slopes. At Hells Gate on British Columbia’s Fraser River, human activity has made a natural obstacle daunting for fish. Here, the river squeezes through the space between two unyielding shoulders of erosion-resistant granodiorite in a swirling maelstrom of water that, depending on the season, is often deeper than it is wide. The formidable passage became even more hostile in the early 20th century when railroad construction along the Fraser Canyon’s steep walls triggered a landslide that partially choked the river, making the bottom rougher and the water more turbulent—conditions challenging for salmon heading upriver to spawn. Decades of low salmon runs followed. In the 1940s, engineers built fish ladders in protective tunnels bored through the rock or built alongside the banks, creating a swimmable path home.
Norway, the world’s undisputed leader of salmon farming, raises fish in densely populated sea pens. Fish farmers need to locate their pens with animal welfare guidelines in mind, which include limits on the speed of ocean currents. To determine the maximum flow that the fish should be subjected to, scientists put salmon in tubes and slowly increased the current until the fish did the piscine equivalent of stumbling off the treadmill. (In this case, toppling back against a screen at the end of the tube.) But some scientists recently noticed flaws in the model. Farmed salmon swim in dense groups, which makes swimming easier for individual fish. Also, as currents strengthen, salmon switch from steadily beating their tails to a more efficient “burst and glide” movement, which they can’t do in a narrow tube. So the scientists designed a more realistic test. They scaled up the tunnel, put groups of salmon inside, and turned up the flow. The verdict: a group of average adult salmon can handle a current of about three and a half kilometers per hour before they hit the wall.
The point of breathing is to keep a constant flow of oxygen passing over lung tissue. Most fish need a constant flow of water over their gills for the same reason—which is why they flap their gills, open and close their mouths, or continuously swim. So when fish are caught in nets and can’t move through the water, they struggle to stay oxygenated. That’s an issue for fish in catch-and-release programs or for those snagged as by-catch. These fish are the wrong size or species, and fishers are legally obliged to throw them back, even though the fish may have already asphyxiated. In 2001, researchers discovered that if they put netted salmon—even those that appeared to be dead—in an oblong coffin-like box and ran water along their bodies, many revived. In one experiment, death rates plummeted from more than 50 percent to two percent. But the boxes were too large and clunky for most recreational fishers to have onboard their boats. Enter the salmon recovery bag—a tubular bag attached to the boat’s hull. Slip in an ailing salmon, move the boat forward, and you might just save a fish.
The Feeding Tube
The salmon cannon aims to keep fish alive. But the fish pumped through the tube at the University of British Columbia’s Open Water Research Station in Port Moody are decidedly dead. The tube is a pipe that pumps bits of herring and capelin into the inlet, and can be adjusted to spit out these morsels at different depths. This food lures marine mammals, especially the four Steller sea lions that are trained by the Vancouver Aquarium to work at the research station. By adjusting the pipe’s depth, scientists can study diving and hunting behaviors in situ. That’s what master’s student Aaron Purdy did when he studied the sea lions’ hunting energetics. To attract the animals, he pumped the food through the tube at a depth of 12 meters. Then he lured the sea lions into a breathing chamber at the surface, again using pieces of fish. The chamber captured the sea lions’ exhalations, telling Purdy how much energy they burned. Combining this data with the dive distance down to the fish delivery tube, Purdy could explain how these sea lions balanced dive time and recovery time.
The Other Feeding Tube
In Sweden and other Scandinavian countries, salmon comes in a surprising form: squeezable food tubes. Multiple brands offer the salmon-paste lover a variety of options. While salmon is a noteworthy example, Scandinavia has long had a penchant for food in tubes, including mustard, cheese, and even caviar. Tubes are a good way of preserving perishable foods because they minimize exposure to air compared to other containers such as jars. This tubular predilection seemed to begin after the Second World War. A recent paper from Sweden suggests that it emerged from a perfect storm of innovation and a rise in consumer culture. Add in a booming fishing industry and an appetite for fish and you get the original salmon in a tube.