On a recent walk along Scusset Beach along Cape Cod Bay, the wrack line was dotted with four-pronged, dark-brown, leathery pouches. These pouches, sometimes called “mermaid’s purses”, “devil’s purses” or “sailor’s purses” are actually skate egg cases.
Although many species of skate and shark lay similar egg cases, based on the size, shape and location where they were found, these dried black leathery cases are likely from the Little Skate (Leucoraja erinacea). Little Skates can be found from Nova Scotia to North Carolina, and are a dominant member of the bottom fish community in the northwestern Atlantic Ocean. They prefer sandy or gravelly habitats between the shore to a depth of 300 ft, although they have occasionally been found much deeper. They do not undergo large migrations, but they do shift between shallower water in the summer and deeper water in the winter.
Unlike many species of fish that lay hundreds or thousands of eggs at a time (or more!), Little Skates lay only two of these 3-4 inch egg cases at a time. Each case surrounds a single egg with a large yolk, attached to the substrate in relatively shallow water (less than 90 feet deep) with a pair of curly tendrils. These tendrils are rarely still evident by the time the heavy surf has dislodged the egg cases and deposited them on the beach. On the other hand, the two pairs of distinctive “horns” are usually still intact. These horns at each corner of the egg case serve to absorb oxygen from and release waste to the surrounding water while the skate embryo is developing. One set of horns is approximately half as long as the case itself and curved inward, while the other pair is about as long as the case and nearly straight.
These egg cases protect each embryonic skates as it develops, until it emerges as fully formed miniature adult, ready to fend for itself. Click here to see a Little Skate hatching from one of these egg cases. Over time waves and currents detach the empty egg case from its anchoring point, and often wash it up on shore. This means that by the time we see these odd pointed objects, the baby skates have long since vacated their cases.
The opening left from where the baby skate exited the egg case.
Like sharks, skates (along with rays) are classified apart from the majority of fish that have bony skeletons. Skates, rays and sharks have skeletons composed of cartilage. Another distinguishing feature is the absence of an air bladder; skates must keep moving or they will sink to the bottom. Fortunately for skates, this is where they spend most of their time. They are bottom dwellers, and tend to lie still much of the time, mostly covered with sand, waiting for prey, while only their eyes and spiracles (openings for breathing) are visible.