A chancy idea to breach the sandbar early at Pescadero Marsh has successfully prevented a massive die-off of endangered fish species, according to government experts.
Scientists with the National Oceanic and Atmospheric Administration say not a single dead fish was found on the shores of the marsh since the sandbar naturally ruptured on Nov. 30, leading them to believe a new strategy taken this year was effective in saving the species.
“I would absolutely say that it worked,” said Pat Rutten, a NOAA regional supervisor. “Call it luck or whatever you want. It was a scientific guess, and it worked.”
Described as one of the largest and most unique habitats on the California coast, Pescadero Marsh features 10 threatened species, including two listed as federally endangered: the tidewater gobi and the San Francisco garter snake. But for years, independent experts and local citizens have warned the marsh was becoming a lethal environment for its native fish, particularly the steelhead trout.
Every year around late fall, the ocean tides burst through the marsh sandbar, turning the closed lagoon into an estuary. In some years, the water currents stir up toxic substrata on the bottom of the marsh, depleting the oxygen in the water and causing a mass suffocation of the fish in the water.
Following the natural breach last year, observers found 235 dead steelhead trout, a federally protected species.
Arguing that any remedy was better than doing nothing, Rutten and other experts for the first time this year proposed breaching the sandbar months early. They believed this would keep the water oxygen levels stable, but that outcome remained a theory. Other communities on the California coast also conduct planned breaches on seasonal sandbars, Rutten explained, but these were typically done to protect property, not for species conservation.
On two workdays in October, volunteers dug a channel about the length of a tennis court to connect the freshwater marsh to the ocean waves.
The project gained the backing of state and county lawmakers, but it also raised concerns among stewards with the California State Parks system. Some skeptics warned that engineering changes to the habitat would have unintended consequences that could worsen the marsh.
“We definitely would’ve been vilified if anything went wrong,” Rutten said. “There were a lot of people saying that what we were doing might be harmful … but we knew that doing nothing would have caused another fish kill.”
Based off the success of the trial, Rutten indicated that his agency would continue annually breaching the sandbar in future years until a more permanent solution for the marsh is put forward.
Starting early next year, a state-sponsored science panel will begin investigating solutions to save the marsh species and prevent an associated flooding problem afflicting the Pescadero community. The group will be headed by John Largier, an oceanographer specializing in estuaries from the University of California, Davis. Other panel members are still being chosen.