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By Mark Hume, with Photography by Nick Didlick The Adams River sockeye hesitate when they hit the Fraser Plume on their return journey. The first fish arrive as early as August and the run continues to build until mid-September. Starting in the spring, with early chinook, runs of coho, pink, chum and sockeye have been locking on to the freshwater signature of the big river and turning in out of the Strait of Georgia. Some of the runs bolt straight into the mouth and vanish. But the Adams stock does not. Sometimes for weeks the fish feed heavily just outside the estuary in an area known as the Sand Heads. . .
Hinch, a biologist with the University of British Columbia’s Westwater Research Centre, headed a research team that in 1993 gained some profound insights into the life and death of sockeye in the Fraser River. He learned, among other things, just how crucial energy loading is to migrating salmon. Using new technology developed by Lotek Engineering of Ontario, Hinch wired sockeye with highly sophisticated radio transmitters. For years researchers have followed migrating fish by fitting them with tiny electronic devices that emit a radio signal, tracking them with handheld receivers. But Lotek’s equipment allowed Hinch to do far more than just follow a beeping noise up the Fraser. The signals he and his research team received came from electronic transmitters that were surgically implanted into the fish’s muscles. The operation, which takes seven minutes, leaves a salmon with a thin antenna, like a guitar string, trailing from its belly. From the radio signals it is possible to tell not only where a fish is, but when it’s resting or moving, how much energy it’s using, and the temperature of the water it’s swimming through. As he followed salmon after salmon from Yale up to Hell’s Gate (a 20 to 36 hour journey at speeds of 0.8 to 1.5 km an hour) Hinch began to see the Fraser in a whole new way. He began to see it like a salmon. “It was almost like being in the mind of the fish,” he said of the countless hours he spent tethered to salmon by electronic signals. As he trailed the sockeye he saw how they hugged the bottom in sections, slipping under the heavy main current of the river. He saw how they nosed into cracks and crevasses in the riverbank, hiding from the current like fry, and how they ducked into the mouths of small streams to get out of the Fraser’s silt. During one spate he waited for the better part of a day while his tagged sockeye held in the clear water at the mouth of a small creek. The fish wouldn’t move until the silt load in the Fraser had dropped. He saw how some fish swam day and night, and how others halted abruptly the moment the sun set. And he noted how some fish became disoriented in the powerful back eddies, sometimes swimming around and around for several hours.
Sections of the river that had seemed innocuous took on new significance when Hinch learned how the salmon labored to get up them. Certainly it was no surprise that salmon had trouble negotiating rapids in the canyon, but what he hadn’t anticipated was the huge amount of energy needed to pass through apparently easy sections of the river. The biggest problem: relatively shallow, fast-moving water flowing through narrow channels created by gravel bars. Hinch found that as the summer progressed and water levels dropped, salmon had an increasingly difficult time getting upriver. Eventually he recorded more than a dozen choke points where fish struggled to make headway. . . When a salmon enters the river it stops eating. The energy reserves it carries with it are all that it has. As each day passes, the salmon loses a percentage of its body weight as it burns up the fat it has stored for the journey. By the time it has reached its home river and completed spawning, its weight has dropped by two thirds. Some long-running stocks only have a few days of fat reserves, so any delay in the migration can be fatal.
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