Department of Fish and Game (DFG) biologists are trying a new tactic to help California's ocean-bound juvenile salmon survive. On May 3 DFG staff used a boat to move approximately 100,000 Chinook smolts down the Sacramento River to San Francisco Bay.
“We've been using trucks to transport smolts to points downstream for years, but we've never moved them by barge, and we've never moved them this far," said DFG Environmental Scientist Colin Purdy, who supervised the boat transport to the Bay Area.
Salmon return to their spawning by smell. The imprinting begins before birth as waters flow over the eggs and continues as they grow and make their way to the ocean. Each segment of water on their journey has distinctive chemical clues, which they can re-trace to their spawning grounds. To replicate this, when they are barged downstream water is circulated through pumps from the Sacramento River into the boat's holding tank.
All 300,000 fish in this study were implanted with tiny coded wire tags to help scientists keep tabs on them. The study is being conducted by DFG fisheries biologists with the support of the Commercial Salmon Trollers Advisory Committee, which donated the use of the boat, fuel and crew time to help ensure a successful start to the study.
Scientists hope to confirm that -- unlike the usual method of transporting the fish by truck -- the boat transport will both eliminate in-river hazards such as getting lost or being eaten by predators, and give the smolts a chance to imprint on their native stream on their way to the ocean, improving their chances of successful return.