August Algal Bloom Causes Concern for Future of Bay Area's Sturgeon

When thousands of dead fish began washing up on Bay Area shores last August, the result of a harmful algae bloom, researchers were alarmed to see hundreds of sturgeon carcasses among the dead. 

The Bay Area's population of the long, spiny fish which date back to the dinosaurs have already had a rough run of late in the state's prolonged drought, and the die-off sparked fears for their already tenuous future. 

"What we’re very concerned about," said Andrea Schreier, assistant professor at U.C. Davis' Dept. of Animal Sciences, "is the carcasses that we saw only represent a small portion of the sturgeon that perished in that event." 

The California Department of Fish and Wildlife received reports of 677 white sturgeon carcasses and fifteen green sturgeon in the die-off, though the department said it was still sorting out duplicate reports and expects that number to go down. 

But researchers like Schreier believe the true number of sturgeon killed in the event is actually much higher because dead sturgeon are likely to sink to the bottom or be pulled out to open water with the tides. 

"So the fear that sturgeon biologists have right now," Schreier said, "is that we can’t fully quantify the amount of mortality, we know that hundreds died but it could actually be thousands." 

Sturgeon researchers said the brawny fish, which can live more than a century and reach six feet in length, are much more fragile when it comes to reproducing. They don't reach sexual maturity until they're ten to fifteen years old and don't spawn every year. 

Living their lives in both the freshwater of the Sacramento Delta and the saltwater of the bay, their twin habitats have been impacted by the state's crippling drought. Experts believe the drought, along with treated wastewater from the Bay Area's sewage plants contributed to August's algal bloom, also known as a red tide. 

"We know from recent research the viability of the whole population is really dependent on the survival of adults," Schreier said, "and the adults seem to be the size class that was affected a lot by this harmful algal bloom." 

The biggest fear of the impact of the die-off is to green sturgeon, which are listed as federally threatened. Their sport fishery was shut down by the state in 2007. 

"Any extra loss of individuals of green sturgeon puts them closer and closer to extinction," said Jon Rosenfield, a senior scientist with environmental watchdog Baykeeper.  "When hundreds or thousands of them die that’s a significant blow to their populations." 

While green sturgeon are currently off-limits to fishing, white sturgeon are a prized catch for anglers on the San Francisco Bay for their meat and caviar. In light of the die-off in August, researchers are urging the state to review its fishing regulations for white sturgeon. 

"After a blow to their population like this summer’s catastrophic die-off," Rosenfield said, "it’s a good question as to whether we can continue to have a fishery, at least in the near-term." 

A spokesman for California's Dept. of Fish and Wildlife said the agency is concerned for the future of green and white sturgeon, but has not taken any steps yet to change current fishing regulations. 

Schreier said with more algal blooms likely in the drought-ridden state, the state should consider other options for the sturgeon fishery. 

"One of the actions we were suggesting," Schreier said, "is to switch, even temporarily, from a harvest fishery to a catch and release fishery." 

Schreier's office at U.C. Davis is decorated with sturgeon-inspired bart, from magnets to drawings and scientific charts. She's fascinated by the fish, from their strange look to their peculiar reproduction traits. She sees them as a fish that's survived since the time of dinosaurs, now struggling to survive climate change and the modern industries of humans. 

"So we’re worried this large mortality event," she said, "is going to cause the population to decline faster than what it was already."