Bat ray feeding fun!

Bat rays are beautiful and fascinating animals.  They are the largest ray typically found in the cold waters of California and are capable of pusuing prey buried up to a meter deep in sand or mud!  Once they find their favorite snack, they have powerful jaws and flat, pavement-like teeth to crush the hard shells.  For more on how they find these buried treasures see From form to function: Stingray sensory superstars.

• Location: Bodega Marine Lab, Bodega Bay, CA
• Purpose: To see if bat rays, Myliobatis californica, exhibited preferences between prey types and to observe feeding behavior.
• Study subjects: Sophie, Abby, Jay, Tommy, caught by hook and line, released back to the Bay

Research: Bat rays feed on a variety of benthic invertebrates and fishes, with clams making up a large part of the diet, particularly as the rays get larger.  I conducted prey choice trials to see if the rays preferred a certain species of clam.  I also filmed rays feeding to observe search behavior, prey capture and food processing.

Results: Evidence suggesting preference for Washington clams was observed.  Prey processing was extensive with rays carefully separating hard and soft parts of prey, hard parts were scraped clean and left in a pile before the ray moved on.   Processing sometimes lasted on the order of 10 minutes or more!

Summary: This preliminary study suggested that bat rays may show selectivity when feeding and invest a relatively large amount of time in careful prey processing.  Sophie occasionally tasted and rejected M. nasuta clams whereas all S. nuttalli were consumed if tasted.  During these trials Sophie didn't have to do any hard work to dig up these clams, but normally she would.  How does she identify the right clam to dig for before she expends all of that energy?  Learn more about prey location by bat rays in From form to function: Stingray sensory superstars.  For some photos of beautiful Bodega Bay see Adventure.

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