by Bonnie Henderson
There’s no real beachcombing season in Oregon. There’s only beachcombing weather, and that means storms, most common and most boisterous in winter and spring. Storm winds blow long-traveled ocean debris onto the beach. And big enough storm waves can stir the nearshore ocean down to the ocean floor. That’s when skate egg cases are more likely to land on the beach.
Commonly called “mermaid’s purses,” egg cases found on the beach are typically lumpy, black, leathery pouches about a foot long and half that wide and come from our most common skate species, Raja binoculata (big skate), though beachcombers here occasionally find little starry skate egg cases (4 inches long).
Skates look and swim like rays and, like rays, are close relatives of sharks. Rather than spawning, as most fish do — releasing eggs and sperm into the water — or birthing live young as mammals do, the female skate deposits her fertilized eggs (just one per egg case for starry skates, up to eight for big skates) in a pouch formed inside either of her two uteri, and expels it onto the ocean floor, usually at a depth of about two hundred feet for big skates, which off Oregon means within a few miles of the shore. Hundreds of skates may cluster their egg cases in the same skate “nursery.” Her job done, the female swims away, leaving the eggs to gestate on their own for a full year before — triggered by chemical cues in the developing skates’ brains —the corners of the case open to allow seawater in and, ultimately, to let the young skates out.
The blackish pouches beachcombers typically find are empty egg cases that have done their duty, but sometimes dark olive-green cases still filled with developing eggs get dislodged and thrown onto the beach. Save the skates? Unlikely. By the time you’ve found that egg case, it’s probably been out of the aquatic environment too long for the eggs to remain viable.
Contact: Phillip Johnson, Executive Director, (503) 238-4450, or EMAIL