Unusual numbers of purple sea hares wash ashore near San Francisco

© Morgan Dill
Giant sea slugs called sea hares have been washing up in some East Bay beaches in unusual numbers this summer.

Giant sea slugs have been washing up on some Bay Area beaches in unusual numbers this summer, and some folks who aren't sure what the creatures are actually calling police thinking they've made a grisly discovery.

The big purple blobs, called "sea hares," are invading East Bay beaches and waterways to the wonder and curiosity of beach combers and naturalists. Because they're so strange looking, some beachgoers have even called 911 thinking they're body parts that have washed ashore.

"They're about the size of a human organ, and that's almost what they look like," said Morgan Dill, a Naturalist with the East Bay Regional Park District.

By the time they wash up, they're typically dead. Dill was fascinated when she found one that was still alive, and picked it up to take a closer look. Most people, however, though excited by the discovery find they're not the most pleasant-looking sea creatures, especially with the mess of purple ink they leave behind.

"They're usually pretty grossed out because they are kind of disgusting looking at first," said Dill.

Sea hares can weigh as much as 15 pounds and grow to be more than 30 inches long.

"There was a [sea hare] population boom about a year ago and what we're seeing is, after a year, they lay their eggs and they die and we're seeing them wash up on shore," Morgan Dill, a naturalist with the East Bay Regional Park District told KPIX.

© East Bay Regional Park District
Sea hare eggs on the beach look like a ball of wet egg noodles.

Sea hares look like giant snails in the water. They lay eggs which look like noodles in the bay then they die.

East Bay Regional Park District naturalists say the large number of dead sea hares washing up on shore is unusual, though they believe this is the second such mass die-off here in the past 15 years.

Scientists aren't certain what's behind the current population boom but one theory is that sea hares tend to reproduce more in warmer water. And bay temperatures are on the rise.

"The life cycle of a sea hare is about one year so, after that year of population boom, there's a massive death," Dill said.

Naturalists say the slugs are OK to look at and touch, but they advise not to take them home, rather leave them behind on the beach.