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Date of Award


Document Type


Degree Name

Master of Science (M.S.)


Graduate School

First Advisor

Steven Obrebski

First Committee Member

James A. Blake

Second Committee Member

John D. Hopkirk


The Bat Ray, Myliobatis californica Gill, occurs from Oregon to the Gulf of California and is common in California bays during the spring and summer. MacGinitie (1935) observed that during its feeding activities, the Bat Ray can dig channels up to 1 meter wide, 50 cm deep and 4.5 meters long in benthic substrates. In intertidal sand flats in Tomales Bay, California, circular pits up to 1 meter in diameter and 20 cm in depth are made by Bat Rays in late summer. In some areas over 50% of the sand flat surface is covered with Bat Ray pits. This recurrent seasonal disturbance of the substrate due to Bat Ray predation on benthic communities may be important in affecting their structure and faunistic composition. In preliminary studies of the effects of predation on benthic communities in Tomales Bay, we were interested in obtaining information about changes in diets of Bat Rays in relation to size.



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