From the Bureau of Reclamation:
The fish along this stretch of the Stanislaus River practically jump on the line, and that’s a good thing for the people that have gathered here on a recent fall morning.
The species in question, Oncorhynchus mykiss, the rainbow trout, are well-known to angling enthusiasts – a feisty fish that punches above its weight when caught. Rainbow trout are one of nature’s oddities. In one life history iteration, they remain in the cold, fresh water of Central Valley rivers such as the Stanislaus. Some fish, however, choose the anadromous life. These fish, referred to as steelhead, make the arduous journey to the Pacific Ocean before returning home to spawn.
The Central Valley steelhead, a distinct population segment listed as threatened by the Endangered Species Act, is why Reclamation and its partner agencies are investigating the details of how the fish live and survive.
On the chilly and surging Stanislaus, the process unfolded – fish were pulled from the river with the aid of an expert fly fisherman, tagged and then released back to the water, none the worse for the experience.
“Our goal is twofold,” said Bryan Matthias, fish biologist with the U.S. Fish and Wildlife Service. “Estimate the survival of the fish that are staying here and figure out how many are leaving.”
It’s part of Reclamation’s commitment to fund advancement of science on steelhead to support life cycle monitoring of Central Valley steelhead, a portion of which covers fish tagging efforts.
That effort hinges on what’s called the juvenile production estimate, the launch point for knowing the overall abundance of steelhead in the watershed and beyond. It’s part of a steelhead science plan that stands to be the basis for understanding the status and trend of the fish each year.
That’s important for Reclamation, given that water operations are sensitive to the presence of steelhead at or near the export facilities. A juvenile production estimate is expected to be a meaningful threshold can be developed to further reduce affecting steelhead populations due to water operations according to Reclamation fish biologist Chase Ehlo.
The need is evident. Central Valley steelhead monitoring “is very limited, not standardized, and lacks dedicated funding,” according to the California Department of Fish and Wildlife.
Scientists rely on two tagging methods for the fish. Passive integrative transponders, or PIT tags, are relatively inexpensive, with unique identifiers, no batteries and activation by special antennas. It’s the same technology used to help reunify lost pets with their owners.
The other technology, acoustic telemetry, uses battery-powered tags that emit sound waves that can be detected with special receivers. They are more expensive than PIT tags with shorter battery life but have a much greater range.
“The acoustic tagging not only allows us to estimate out-migration rate of steelhead smolts, but it also allows us to estimate survival and routing of those out-migrating smolts through the Delta on their way out into the ocean, as well as to track movements and survival of the resident rainbow trout that opted to stay in the river,” said Ehlo with Reclamation. “All of these things will help us to better understand the species life history and provide a basis for informing impacts from water operations on species.”
For fish that battle multiple stressors in a radically altered system, tagging is one of the methods experts use to sharpen their knowledge and better inform management decisions.
“In the greater scheme of things, it is one of the tools,” said Matthias. “There’s no one [tool] that is the best thing ever. It takes a lot of effort to do this.”
