Can the city help? Can you? Will decimated species rebound?


The astonishing die-off of marine life in Oakland’s Lake Merritt and other parts of San Francisco Bay continued Monday evening, and by Tuesday morning visitors to the lake saw tens of thousands of stranded anchovies. The small silvery fish crowded around large rotting striped bass, rayfish and smelt that have died in the last 72 hours. Lake walkers stopped to watch the morbid scene as a sulfuric stench rose from the brackish fetid water in nearby neighborhoods.

Oaklandside caught up with Damon Tighe, a naturalist who documents Lake Merritt wildlife, to verify the latest findings of the algal bloom believed to be the cause of the fish kills.

As he stood in the mud near the Chalet Lake waterfront restaurant to get a close view of the recently deceased shrimp and clams, a random passerby stopped and shouted at us, “I don’t never realized we had so many fish in the lake!

“It’s a sad way to find out,” Tighe said as he gazed at the floating carcasses of large fish.

What causes fish to die?

A dead bat ray surrounded by sun-baked anchovies and prawns. Credit: Amir Aziz

The fish are probably dying because they can’t breathe.

The algal bloom has been growing in the bay and lake since at least July, when it was first spotted in the waters off Alameda Island. Called Heterosigma akashiwo, the microscopic life form turns water a syrupy brown as it multiplies. At some point, it becomes so prolific that it begins to consume all available oxygen, causing fish and other life to suffocate.

Tighe said the algae photosynthesize during the day and respire at night. As a result, nighttime is when oxygen levels in the lake drop most rapidly and is when fish seem to die off in greatest numbers.

Volunteers with the Rotary Nature Center Friends group, which does education and advocacy for the lake, have been testing oxygen levels in the water for many years. Recently, the amount of dissolved oxygen in water has dropped.

Group co-chair Katie Noonan said she tested the water on Sunday and found it had less than one part per million dissolved oxygen, a very low amount. “Lack of oxygen would kill many fish and other organisms with or without toxin,” she wrote in an email. “I don’t think we know if a toxin is involved. It could be both. »

Some have speculated that another species of algae was releasing toxins into the water that were killing fish, but so far no one has shown dangerous levels of known toxins in the lake or in any other parts of the bay.

Where do algae come from?

Damon Tighe collects scum samples at Lake Merritt. Tighe and other researchers are trying to find out more about the massive fish kills. Credit: Amir Aziz

Flowering of Heterosigma akashiwo is natural and occurs every few years, but rarely in such incredible abundance.

Tighe explained that this organism is always present in the water, but that it spends part of its life in the form of a “cyst”, similar to a seed which floats or rests in the sediments, waiting for the conditions to be right. grow, bloom and reproduce.

For various reasons that we do not yet fully understand, conditions are currently ideal for Heterosigma akashiwo to thrive. We know that algae need nitrogen and phosphorus to feed themselves. Some have speculated that sewage flows into the bay from the many sewer districts where human and industrial waste could provide these nutrients.

A study from a red tide that killed fish in Florida last year showed the sewage made the deadly event worse for fish and other wildlife. Others wonder if there has been excessive runoff from agricultural fields in the Central Valley this year.

What is dying in Lake Merritt, what is at risk, and can it all bounce back?

Young brown pelicans feed on the few remaining schools of anchovies that have so far managed to survive. Credit: Amir Aziz

Fish are the most obvious victims of algal blooms. On Tuesday, Tighe reported half a dozen species of fish that have perished in the past 48 hours. The large bodies of fish were clustered in the densest groups along the shore of the West Arm of Lake Merritt. Tighe counted more than 500 dead striped bass and dozens of dead bat rays.

But he said he noticed something new and disturbing today: lots of dead clams and other bivalves. Many crabs were also suffocated by seaweed. He was also sad to find his first mud shrimp, a large crustacean that looks like a cross between a shrimp and a lobster, among the dead.

Three large striped bass and hundreds of anchovies killed in the last 72 hours. 1 credit

Seeing large fish, some of which take many years to mature, die in such large numbers made Tighe think of the 2020 CZU lighting complex fire in Santa Cruz, which burned not only shrubs and grass, but killed many old redwoods and other trees. “Anchovies could rebound in a year or two,” he said. “What’s really hard to see is that the old stuff is dying.”

He added that the collapse of small species of fish, clams, crabs and other invertebrates could become large enough to have cascading impacts throughout the food chain. Any large fish that survive the algal bloom will end up with fewer food sources. And birds will find hunting on Lake Merritt and around the bay much more difficult.

Catherine Becker, an avid birdwatcher we met while walking around the lake, said she was worried about pelicans and other seabirds consuming anchovies, herring and other fish.

Countless clams and other small invertebrates are also dying right now. 1 credit

“They’re behaving very strangely,” she said of a large flock of brown pelicans that had massed in the western arm of the lake.

Brown pelicans often dive into their prey, diving into the water above a school of fish to suck them into their ample throats. But today pelicans swam to the surface, hastily chasing a few small schools of anchovies that have so far avoided dying overnight.

“I’m really freaked out,” Becker said. “I guess we’ll have to save a lot of birds.”

The entire San Francisco Bay, but especially Lake Merritt, is an important stopover for migrating birds, Tighe noted. If fish populations drop because of the red tide, it could interfere with that. “We could see starvation,” he theorized.

What could the city do to help stop the mortality?

A work crew lifts one of the lake’s fountains out of the water so it can be repaired. Credit: Amir Aziz

The algal bloom appears to be driven by tremendous forces of nature and possibly human causes far beyond Oakland’s control. Think of atmospheric and ocean cycles, climate change, sewage flows from San Jose to Marin County, and agricultural runoff.

But one thing that could help prevent more fish from dying is getting more oxygen into the water. With the help of the Lake Merritt Institute, the city operates several large fountains, one at the end of the west arm of the lake and one near the pergola. Pulling water from several feet below the surface and spraying it into the air replenishes oxygen in the lake.

Both fountains have been out of service for some time now. On Tuesday we saw workers transporting one of the fountains to the Lake Merritt Boathouse where a mechanic said he was replacing the motor so it could be put back in place and turned on, possibly as early as tonight.

Tighe said the fountains could save fish in the immediate area. It would also help if the wind picks up. Opening the tidal gates that allow water from the bay to flow in and out of the lake could also help oxygenate the water.

Earlier this morning, the city released a update on other measures it is taking to remedy the situation. He is awaiting the results of tests conducted August 22 by the San Francisco Bay Area Water Quality Control Board to better understand what is causing the fish kills. In the meantime, the city is working with a contractor to clean up fish carcasses “to mitigate odors and public nuisance ahead of the expected hot weather and long weekend,” the Oakland Public Works spokesperson wrote. , Sean Maher, in an email.

Can the people of Oakland do anything to help?

People walking on the lake stop to take photos of the dead fish lining the shore. Credit: Amir Aziz

The Oaklandside met several volunteers from the Lake Merritt Insitute near the amphitheater on the southern edge of the lake. They were preparing with tools from one of the institute’s many utility boxes arranged around the lake to do some cleanup on their own.

A volunteer named Tim said he planned to remove the larger fish carcasses while leaving the smaller ones on the shore. He added that anyone can help clean up the lake. Interested persons should Contact the Lake Merritt Institute.

David Wofford, a member of the Friends of the Rotary Nature Center, told The Oaklandside that he hopes the massive fish kills will open the eyes of people who haven’t given much thought to Lake Merritt. He said he hopes more people will volunteer with groups like his because lake health is a group effort that requires a variety of skills and knowledge.

While having lunch near the boathouse on Tuesday afternoon, Wofford said he and a friend were about to kayak to the center of the lake to take measurements of oxygen levels in deeper water. “People should be involved for the long term,” he said.


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