Thousands of anchovies swarmed the Santa Cruz Harbor near Seabright Beach.
(Santa Cruz Harbor via Instagram)
Coast Life

Santa Cruz Harbor’s anchovy invasion is over — for now

Thousands of anchovies have found their way back into Monterey Bay after they swarmed the Santa Cruz surfline and small craft harbor near Seabright Beach. Though harbor staff is not sure why this phenomenon occurs, they are glad this iteration was quick and that they do not have to oversee any large-scale cleanup efforts.

The Santa Cruz Harbor escaped a smelly situation, evading a massive die-off of anchovies that swarmed into the harbor last week.

Local coves, surflines and the harbor were all packed with thousands of the small fish last week. When the anchovies similarly stormed the harbor nine years ago, a huge number died, leaving them to float in the port’s still waters and causing an unpleasant fishy stench to permeate the beaches and coastal air.

This time, however, there will be no offensive odors as a result of the anchovy deluge. The fish came into the harbor last Monday, and by the end of the week, most of the anchovies were out of the harbor and back in the ocean, said Senior Deputy Harbormaster John Haynes.

Haynes said that he and the rest of the harbor staff aren’t even sure why this happens. He said historically, the assumption was that the fish were escaping predators and migrating closer to shore to do so. Now, he hypothesizes that it might be due to some kind of cyclical water condition like an oxygen saturation issue. Temporarily low oxygen levels farther out in the bay could drive the fish closer to more aerated water near the surf.

Haynes said that the harbor can expect some extent of an anchovy invasion in the mid- to late summer every year, and it’s just a matter of how intense the influx will be. Regardless, the staff utilizes aerators — a mechanism that pumps air into the water — to try to keep oxygen levels high enough for all the fish to survive in the crowded environment.

“It’s just an electric motor connected to a shaft that has a propeller on it,” said Haynes. “That’s really the only thing that we’ve been able to do to help the fish stay alive when they come in with those numbers.”

Haynes said that when harbor staff first noticed the high anchovy levels last Monday, oxygen conditions in the water were normal, but by Tuesday, oxygen levels had nosedived. The huge number of anchovies had already used up much of the harbor water’s oxygen.

Thousands of anchovies swarmed Santa Cruz Harbor near Seabright Beach.
(Santa Cruz Harbor via Instagram)

“That directly corresponds with the health of the fish. First, they start jumping to the top of the water because they’re agitated, and second, they get sluggish,” he said. “Then if things get worse, they start losing their orientation in the water which is when they start dying.”

Luckily for harbor staff — and all coastal dwellers, for that matter — oxygen conditions rebounded by Wednesday, and by Thursday most of the fish were out of the surfline and harbor and back into the bay.

“It very much was a direct corollary. When the fish came to the surfline, they came into the harbor, and when they left the surfline, they left the harbor, too,” said Haynes.

So did the aerators do the trick? It’s hard to tell, said Haynes. He said that they do seem to work, but there has not been much empirical testing to determine just how effective they might be. Regardless, running the aerators is never ideal.

“They use a lot of electricity, so they’re really expensive to run,” said Haynes, adding that the harbor might have to keep aerators running from July to September if a major anchovy inundation lasts long enough.

Thousands of anchovies swarmed the small craft harbor near Seabright Beach.
(Santa Cruz Harbor via Instagram)

Haynes said he is grateful that the fish made their way back out into the bay, because the cleanup effort following a massive die-off is not pretty.

“In 2014, we took 120,000 pounds of dead anchovies out to the landfill, and that was just what we collected from the harbor,” he said.

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