Meeting Abstract
75.5 Sunday, Jan. 6 Bite force and performance in the durophagous bonnethead shark, Sphyrna tiburo. MARA, K. R.*; MOTTA, P. J.; HUBER, D. R.; University of South Florida; University of South Florida; University of Tampa kmara@mail.usf.edu
Bite force, used as a measure of performance, may be used to link an organism�s cranial morphology with its biological role. As such, bite force and the morphology associated with it may result in dietary constraints or open new feeding niches. The bonnethead shark, Sphyrna tiburo, is a durophagous member of the family Sphyrnidae. Its diet in south Florida consists almost entirely of blue crabs, Callinectes sapidus, which are either crushed or ingested whole. This coastal predator has a feeding mechanism specialized for the consumption of hard prey, including a modified jaw adductor activity pattern, molariform teeth, and supposed high bite force. The goal of this research was to characterize the biomechanical basis of durophagy in S. tiburo (68-96 cm TL) by determining its bite force. Theoretical maximum bite forces were estimated from three-dimensional musculoskeletal modeling and compared to those gathered during manually restrained biting and tetanic stimulation in anesthetized sharks. These force values were compared to the force required to fracture the carapace of blue crabs (78-115 mm CW). The average maximum theoretical bite force ranged from 25 N at the anterior teeth to 100 N at the posterior teeth. Average anterior bite force during stimulation was 10 N, with a resultant posterior bite force of 37 N. Average maximum anterior bite force from restrained individuals was 13 N. Compared to other durophagous fishes, S. tiburo has a surprisingly low bite force given the proportion of hard prey in its diet. Blue crab fracture forces (100�420 N) indicate that S. tiburo consumes crabs that it may not be able to crush. However, dietary data show that large blue crabs occur less frequently in the diet than do smaller blue crabs indicating bite force may constrain diet.
