Weather Watch

What’s a mermaid purse? You’re about to see them wash up along the Central Coast

Swell shark egg pods at the Central Coast Aquarium in Avila Beach.
Swell shark egg pods at the Central Coast Aquarium in Avila Beach. Special to The Tribune

We are approaching the time of the year when the first massive mid-latitude storms with hurricane-force winds generate high-energy waves. Even though they may not be a typhoon or hurricane, these mid-latitude storms can be some of the most powerful on Earth.

Relentless gales from these cyclones blow across the northern Pacific and can generate unimaginably high seas, well over 50 feet. When these seas move out from under these winds (wind fetch), they became longer-period swells.

These higher-energy swells not only generate large waves that crash on our beaches but also tear up the kelp beds along our coast. After the first big wave event, unfathomable amounts of California giant kelp (which can grow up to 24 inches in one day), bull kelp along with other red, brown and green algae are washed up on the beaches.

As the kelp dries and decomposes, along with shells and other debris have washed up, and you may be lucky enough to discover an otherworldly looking 4-inch-long brown-leathery pod with curly lines attached at each corner that look like top Ramen Instant noodles.

These pods are shark eggs or lovingly referred to as “mermaid purses.” Some may contain a yoke and shark embryo or could be empty. Only a small number of shark species lay eggs, like the swell sharks (Cephaloscyllium ventriosum) or their relatives like skates.

The laying of eggs is called oviparity, and the egg castings come in a variety of shapes, textures and colors depending on the species of shark. Like our fingernails, their egg casing is made of keratin, and most are transparent when held up to the light; you can see the yoke and embryo. Horn shark eggs look like a corkscrew.

One of the most common shark species that lay eggs along the Central Coast is the swell shark. Jami Clayton, coordinator at the Central Coast Aquarium in Avila Beach, told me that they have an unusual behavior when threatened by a predator.

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When in danger, the swell shark will seek a rocky crevice and swallow vast amounts of water that causes it to double its regular size. When it’s wedged in the rocks, it’s difficult or nearly impossible for a predator to remove it.

Like other shark species, they are covered by tiny flat V-shaped “skin teeth” called dermal denticles. In other words, they are covered in teeth instead of scales.

These swell sharks have a 20- to 25-year lifespan and can grow to 4 feet in length and are often called the “puppies of the sea” due to their docile behavior. They are mostly nocturnal, sleeping during the day and active at night. In fact, they may be biofluorescence, which potentially assists in camouflage or communication between each other at night.

The swell shark will typically lay two palm-sized, greenish-amber flattened eggs cases in a rocky, algae-covered location that perfectly match the kelp in color and texture. The tendrils (the wavy lines attached at each corner of the egg casting that look like top Ramen Instant noodles) anchor the mermaid purses to the kelp. The length of the tendrils may depend on the amount of average wave energy to which a kelp bed is exposed.

No parental care is provided after the eggs are laid. The embryo develops for nine to 12 months depending on seawater temperature before hatching.

However, predation presents a significant risk to survival. Gastropods or snails will bore through the egg case and consume the egg yolk and embryo. After hatching, the pups feed on crustaceans, small fish and mollusks.

You can see these sharks along with their mermaid purses at the Central Coast Aquarium. For more information, contact the Central Coast Aquarium at 805-595-7280 or

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A warming climate combined with an increasing numbers of extreme weather events are causing unprecedented and unanticipated wildfires. Launched in late March, the PG&E’s Community Wildfire Safety Program has developed and implemented additional precautionary measures intended to reduce wildfire threats and strengthen communities for the future. These new safety measures are more critical than ever given the dramatically increasing and devastating wildfires the state has experienced during both the 2017 and 2018 wildfire seasons. To learn more, visit

John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at or follow him on Twitter: @PGE_John.
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