Bat Rays, Myliobatis californica, can be found exploring the bottom of the Bay and are native to the West Coast from Oregon to the Gulf of California, preferring intertidal waters and sandy areas. The rays get their common name from their triangular-shaped pectoral fins which allow the ray to swim gracefully through the water with a flapping motion.
Bat Rays also use their fins to locate prey by flapping them to expose buried mollusks, bivalves, shrimps, and crabs underneath the sand, and then using their snouts to dig out the prey. Because bat rays can’t see their prey, as their eyes are located on the top their bodies, they employ a unique sensory system which helps them to locate the prey using an array of pores that detect changes in water pressure throughout its body. The sensory system allows the rays to sense pulses of water expelled by mollusks. Once food is found, their plate-like teeth are used to crush the prey. They then are able to sort out the edible flesh and spit out the hard shells.
Bat rays are typically solitary, often buried underneath sand with only their eyes and moving spiracles exposed. Their dark upper side and light lower side help with camouflage from predators. When looking from above, the dark side is hidden within the depths of the ocean, and when looking from below, the light side blends with the light coming from the surface of the water. If the rays are disturbed when in hiding, they will pop up and swim away with explosive speed. The bat rays can also protect itself from predators, such as sharks and sea lions, with its venomous spine, which causes a sting to any being that casts an unwarranted touch. To avoid being stung, shuffle your feet through the sand to encourage the movement of buried rays – called the “ray shuffle.” They can grow to be large, with females able to reach up to 200 pounds with a wingspan of six feet. Males tend to be smaller.
Oyster growers used to blame bat rays for eating oysters and destroying their oyster beds. To protect the oysters, growers would trap and kill the rays, only to discover recently that crabs, not bat rays, are responsible for the oyster destruction. Crabs eat large numbers of oysters, while bat rays actually eat crabs. Instead of protecting the oyster beds, the growers increased the vulnerability of the oysters by killing off the crabs’ natural predator. While oyster growers are no longer trapping the rays, bat rays are popular with sport fishermen, and even commercially caught for food along the Mexican coast.
Look for this fascinating marine creature in the Bay and along the coastline, including at Elkhorn Slough and Tomales Bay where they are often found.
Photo 1: Aquarium of Pacific, http://www.aquariumofpacific.org/images/olc/bat_ray.jpg, Photo 2: Ocean Conservancy, http://www.oceanconservancy.org/assets/feature-images/carousel/top-10-mpa-species/rays.png
Photo 3:Monterey Bay Aquarium, https://www.montereybayaquarium.org/-/m/images/animal-guide/fishes/bat-ray.jpg?bc=white&h=1357&mh=738&mw=1312&w=2400&usecustomfunctions=1&cropx=0&cropy=166