Scaling of Bite Force Generation in the Cownose Ray

The cownose ray is a source of controversy and increasing media attention due to interactions with commercial fisheries and on-bottom aquaculture operations for bivalves such as oysters, clams, and bay scallops.  Claims of increases in the population of cownose rays coupled with increases in damage to shellfish culture, grow-out, and restoration operations have led to the development of commercial harvesting for cownose rays in regions such as Chesapeake Bay, though no stock assessments have been completed and no management plans exist.  We seek to empirically evaluate the jaw biomechanics of the cownose ray relative to the mechanical properties of commercial bivalve in order to inform management and stakeholders and perhaps suggest alternative means of mitigating interactions.  Preliminary studies indicate cownose rays are bite force and gape limited suggesting bivalve susceptibility to predation decreases ontogenetically.  Gape size limitation hinders or restricts the ability of a predator to process and consume prey.  The ability to manipulate and crush bivalve prey is intrinsic to understanding the effect predation has on commercial bivalve populations.  Forces at which the bivalve shells exhibited catastrophic failure will be compared to measured and theoretical bite force data gathered from the cownose rays.  Measurements of anterior and posterior gape size will be regressed against bivalve dimensions to determine if gape size limits predation.  If cownose rays are not capable of consuming bivalves at a particular size class, this could indicate that once a bivalve has reached a particular size, it is functionally beyond the predator’s ability to ingest (i.e. size refuge).