Anchovies_(4122029675)Monterey’s warm, nutrient-rich waters naturally support a huge population of everything from plankton to large humpback whales, and this summer has been no exception. While a large population of anchovy in Monterey Bay is normally a good sign, a massive school of anchovies swam in on Wednesday, depleted the oxygen in the water, and then started to die en masse.

Even with aerators pumping in oxygen to the Santa Cruz harbor (and a great effort by the harbormaster in doing so), there still wasn’t enough to keep them alive.“We were just really inundated by a big school of fish that overwhelmed the air capacity of our aerating system,” harbor master John Haynes said.

The massive die-off has created a very smelly situation in the process.

The rotting corpses of the small fish (in addition to the waste of sea lions, harbor seals, seagulls and other birds preying on them), has forced a temporary shutdown of the launch ramp at the harbor and swimming advisories posted at nearby beaches. Onlookers have said the smell of rotting fish, combined with the waste of the birds feeding on them and growing bacteria in the water, is overwhelming.

Officials say the same thing happened last year and that it’s happened many times before, but not to this level in recent years. According to Santa Cruz Harbormaster John Hayes, this is the worst fish kill in Santa Cruz since the 1980s.

On Friday, crews at the harbor were using fishing nets to trawl out tens of thousands of dead anchovies around the docks and boats. A sign in a parking lot asked for volunteers to help with the cleaning effort.

There is an upside to the mass death and horrible smell however. The same abundance of deceased anchovies littering the near-shore waters has brought a spectacular array of sea life close to shore.

“We’re seeing a lot more humpback whales,” said Baldo Marinovic, a biologist at UC Santa Cruz and researcher at the school’s Institute of Marine Sciences. “They’re nearly up on the shore.” Whale-watching sightseeing boats along Monterey Bay are also reporting one of their best summers in years. The show of wildlife, Marinovic explained, comes with the upwelling of ocean water near the coast, which has brought nutrients to the surface and had a ripple effect up the food chain.

Interestingly, anchovies have been all but missing for the last 5-10 years before they began to return last year. Why they disappeared and why they returned is unknown.