California Department of Fish and Game (DFG) biologists are trying a new tactic to help the state's juvenile salmon reach the Pacific Ocean, in hopes of increasing survival rates.
Earlier this month, for the first time, DFG staff used a boat to move approximately 100,000 young king salmon -- known as smolts -- down the Sacramento River to San Francisco Bay. Upon arrival, the smolts were released to grow to adulthood before returning upriver to spawn.
"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. "Truck releases are typically much further upstream, and though they do shorten the fish's journey to the ocean, they still face all kinds of hazards in the river. Its possible we could better the chances of survival for this species just by making a few thoughtful changes in our operating practices. The data we collect over the next few years will tell the story, but we're hopeful that we'll see positive results."
Salmon return to their spawning grounds using their sense of smell. The process, called 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 cues which they can re-trace to their spawning grounds. Water is circulated through pumps from the Sacramento River into the boat's holding tank, where the fish are kept. The hope is that this may improve their ability to find their way back as an adult, and predators are unable to access the fish in the holding tank during the journey downstream.
This program is the beginning of a multi-year study aimed at increasing return rates of salmon from the sea to their native rivers. Over the next few years, scientists will use the data collected from the fish to test and evaluate the idea that overall survival rates and increased adult returns can be better achieved by barging the young salmon downstream. To form a basis of comparison for this study, two other control groups of 100,000 smolts each were released by trucks in other locations at the same time as the barge release -- one at a different location in the bay, and one into the Sacramento River near Sacramento. All 300,000 fish in this study were implanted with coded wire tags smaller than a tiny piece of pencil lead, which will ultimately enable scientists to tell which of the three groups the returning fish came from -- the barge release, or one of the two truck releases.
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.
"This has been a major cooperative effort and we really appreciate DFG's willingness to work with everybody and look at new ways of doing things," said Zeke Grader, Executive Director of the Pacific Coast Federation of Fishermen's Associations. "DFG is committed to decreasing straying rates among the salmon migrating up the Sacramento River. Barging may be one way to achieve this goal."
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.