Velella velellas — the pretty ‘by-the-wind sailors’ — are washing ashore by the thousands in San Diego County

Blue Velella velella, also known as "by-the-wind-sailors,” washed up on Carlsbad State Beach at low tide on April 17, 2023.
(Ana Phelps)

Scripps Oceanography says onshore winds and abundant food have led to a rare mass stranding that’s caught the attention of surfers and beach-goers.


In a spectacle rarely seen along the San Diego County coastline, thousands of Velella velellas — or “by-the-wind sailors” — are washing ashore in a mass stranding.

Scientists say it is a natural phenomenon that typically occurs when there is a combination of onshore winds and plenty of food in the water. The free-floating creatures eat pelagic gastropods, notably snails. They aren’t jellyfish but do resemble them.

For roughly the past week, the Velellas have been sighted from Ocean Beach to Carlsbad. They appeared in large numbers Wednesday in and around the Scripps Pier in La Jolla.

“They sort of looked like a little fleet of peaceful sailors,” said Anya Stajner, a researcher at UC San Diego’s Scripps Institution of Oceanography who has studied the species.

Most of the Velellas were dead or dying, which happens when they are carried into shallow waters and onto beaches, where they are fully exposed to lots of UV light.

The Velellas’ body mostly consists of a handsome blue disc with a sail-like vertical crest rising from the middle. They also have tentacles that can deliver a sting, which is generally benign if delivered to humans, Stajner said.

The creatures — which are about the size of a human thumb — sometimes strike fear in swimmers and surfers who mistake them for Portuguese man o’ war, an animal related to jellyfish that can give a very painful sting.

Velellas velellas are passive and travel where the wind takes them. Stajner refers to them as zooplankton that are so nice they were named twice.