Bat Rays in Drakes Estero and Tomales Bay

Bat Ray. Photo by Linda Thomas. 2005

Bat rays are commonly seen in our shallow waters of Tomales Bay and Drakes Estero. Kayaking along, often you will see the tips of their grayish-brown fins flapping just above the surface of the water as they meander through the eelgrass beds. The Bat Rays we find in Tomales Bay are a type of Eagle Ray and you may have heard someone refer to a “bat ray” as an “eagle ray”. Bat rays are sometimes sought after by fisherman for there edible meat. In some areas around the world rays have been overharvested and beaches filled with their remains lie as a daunting reminder to any species fragility.

 Ray Skeletons, Baja California Sur, Mexico. Photo by Tressa Bronner. 2007

Bat rays were eating oysters being farmed in the bay for human consumption, but they weren't the only marine animal looking for a meal.  There was a push by farmers to reduce the predation of their farmed oysters by the rays. With the reduction of bat rays and continued predation of their oysters it was discovered that the rays were actually feeding on crabs that were feeding on their oysters. 

These creatures are fun to watch and it is magical when they swim underneath your kayak.

Kayaking Drakes Estero. Photo by Tressa Bronner. 2009

The Facts:

Size: At birth, these rays are around 8 inches across and are born with their tail wrapped around themselves to protect the mother from the barb on their tail while giving birth. Rays grow steadily until hitting maturity, at which time growing slows. Females are larger than males, ranging 40-70 inches across at maturity. Males range from 23-40 inches across at maturity.

Diet: Bat Rays use ther "wings" to hunt for food. Flapping their pectoral fins in the sand, they expose buried prey, such as clams. Rays also use their lobelike snouts to dig prey from sandy bottoms.

Bat Ray Photo by Linda Thomas. 2005

Reproduction: Males typically live up to six years. Females live longer, up to 25 years of age. In May-July, 2-10 pups are live born after a ten to twelve month gestation period. During mating season, June and July, the rays can be seen in Drakes Estero and near the oyster beds north of Hog Island in Tomales Bay. The rays move into the estero for birthing just as the harbor seals are wrapping up their birthing season.

Range: Bat rays move into open coastal waters as water temperatures drop below 50 degrees F and head for warmer water. They are often seen schooling with smoothhound sharks and leopard sharks as they travel.

Predators: Bat rays are eaten by Great White Sharks, Seven gill sharks, and occasionally by sea lions and humans.

Stay tuned for our next blog about creatures we have been seeing while on the water, leopard sharks.

*Linda Thomas has more photos available for viewing . Check out her ac4it's Flickr page.