Marine Ecology: The Bat Ray

The Bat ray, also known as Myliobiatis californica is one of the denizens of the kelp forest. This creature is identified by a bat-like head and black diamond-formed body. It lingers on the bottom, but when the schools migrate, they move to the surface. They give birth to living young early in the summer. These creatures have a long venomous tail spine behind the dorsal fin with up to three spines that can cause injury and they linger in the sand. They have a taste for crabs, shrimps and other soft invertebrates that live on the bottom. They can get very large, growing up to 6’ and they can weigh over 100 lbs. They range from Oregon to the Gulf of California in Mexico. They are sexually dimorphic with females growing larger than males. They can live up to 23 years. They are alone and school with some schools having thousands of individuals. They have been found in one million year old fossils from the Pliocene deposits indicating that they are an ancient and valuable species.

They like estuaries and sandy areas but they can be found near reefs and kelp beds. They like to bury themselves in the sand. They feed by lifting up and down, making suctions in the sand which helps them find food. They fill a vital role of predator, keeping bivalves, mollusks, crabs, shrimps and Polychaets in check. They use their short, flat teeth to chew bivalves and snail’s shells off. They are caught as bycatch on occasion and are considered least concern. They hide using camouflage. This opportunistic benthic feeder keeps check of fish eggs too. It easts herring, topsmetlt, jacksmelt and midshipman and there are other beings found having consumed crustaceans and mollusks. The larger sharks feed on them, ,and so do pinnipeds. Humans also eat them. It is not exceptionally dangerous despite its stinger. Tracking and tagging will better help us understand this elusive creature.

Males find females by swimming around and once they find one, they follow her watching chemical signals. When the female is ready, the male goes under her, back to her belly and rotates a clasper near her cloaca/ They copulate as they swim together, synchronized beating of wings. Females keep together during the mating season and help males find suitable mates by protecting females that are immature or that have already mated. They are oviviparous which means the eggs are fertilized in their body and they are able to birth their children after one year. The eggs retained in the body are in a brood chamber and it is here the developing embryo gets nourishment from a yolk sac.  They usually have litters up to 10 individuals. Males mature around 2-3 and females around five years. They are sometimes caught by commercial or recreational fishers but are not considered commercial fish. It is hard to assess their numbers.

The bivalves and other beings the bat ray eats fill a variety of niches. They consume foods such as detritus and particulate mater. Then, the ray consumes them, along with fish eggs and later the ray may be consumed by a larger shark or pinniped. These bat rays have evolved into our ecology and they are vital. They both keep species such as fish and crustaceans in check, but they also feed larger species.

SOURCE
Bat Rays, Myliobatis californica http://marinebio.org/species.asp?id=101