By Carolyn Stein, San Francisco Chronicle
Jun 28, 2024 11:00 AM
When Randy Renn, a biologist with the San Francisco Public Utilities Commission, first started monitoring steelhead trout at Alameda Creek near Sunol in 2015, his traps were usually empty. This year, for the first time, he has too many fish to keep track of.
“It’s been a lot of work for sure, but rewarding work,” Renn said, who has been coming down to the creek to catch the trout every day since his fish-tagging season began on Feb. 1. “Just to be here and see that increase, it’s phenomenal.”
The dramatic increase in the steelhead is part of a larger, decades-long effort to restore the habitat of this native species that has been trapped in creeks in the hills and unable to make its migratory journey to the ocean. This year the endangered fish began making the entire journey through Niles Canyon and the final urban stretch to the San Francisco Bay in meaningful numbers.
Last year, the agency detected only one steelhead trout making the journey. This year, scientists have been able to detect 50 fish completing the route.
The restored steelhead population benefits both people and surrounding predators in the area. For Bay Area residents, a healthy steelhead trout population means a healthier watershed, which in turn means better quality drinking water. For predators in the area, such as bobcats, red-tailed hawks and bald eagles, it means they have another food source to choose from.
The Alameda Creek Fisheries Restoration Workgroup — a coalition of public agencies and nonprofits — has worked for 25 years to restore the habitat of the steelhead trout and improve the overall quality of the Alameda Creek watershed.
“There was arm wrestling about whether or not we should do it at all, and then how it was going to be done. And now we’re doing it,” said Tim Ramirez, a manager at the public utilities commission.
During their lifetime, steelhead trout travel between the freshwater creek and the ocean as part of their reproductive process, but in years past dams and floodwater infrastructure have prevented the migration.
The removal of two smaller dams in Niles Canyon east of Fremont, along with the construction of several fish ladders, has allowed the fish to make this journey with ease. Before the construction, the fish had access to only about 9.5 miles of the stream. Meanwhile, the coalition built several fish ladders around the stream, including one that helps the fish get around a concrete structure near train tracks in Fremont known as the BART Weir.
“Previously to the construction at BART Weir, the fish only had access to about 9.5 miles of stream,” Renn explained. “After the fish ladder went in, the fish have 40 miles of stream access.”
To track the fish, Renn has to first capture the steelhead in one of two traps set up along the Alameda Creek downstream from the Calaveras Reservoir. When he goes to capture the fish, he is looking to snag juvenile steelhead, which are usually about the size of a Popsicle stick, contain a pink stripe on their side and spotting on their fins. When they get ready to swim out to the ocean, their fins turn black and they gain silver coloration, and grow to 12 to 16 inches as adults.
Once the fish is captured, Renn puts a tracker about the size of a grain of rice inside the steelhead, giving each fish a unique identifier. He also takes a scale and tail sample from the fish to analyze both their age and genetics. Then, the fish are released into the water.
When the fish are ready to swim downstream to the ocean, they have to bypass the weir, a 12-foot, concrete-slope structure — which is where the ladders come in. To get past it, the fish swim through a series of elevated pools in the ladder. Antennas in the ladder are able to identify which fish are moving past the weir and out to the ocean. When one of the antennas detects a fish with a tracker, that information gets stored in a database and also sends a signal to the Alameda County Water District within four hours.
“We’ve already captured 50 unique tags with out-migrating fish this year, which is great,” said Leonard Ash, water supply supervisor at Alameda County Water District — a huge jump up from last year when the system detected only one fish.
The system has yet to detect any steelhead swimming upstream back to fresh water, but the increased numbers are a reason to remain hopeful that eventually the system will see steelhead return.
“We’re hoping that eventually,” Renn said, “we’ll see the whole steelhead life cycle be completed.”