Advances in the study of feeding behaviors, mechanisms, and mechanics of sharks

Sharks as a group have a long history as highly successful predatory fishes . Although, the number of recent studies on their diet, feeding behavior, f eeding mechanism, and mechanics have increased, many areas still require ad ditional investigation. Dietary studies of sharks are generally more abunda nt than those on feeding activity patterns, and most of the studies are con fined to relatively few species, many being carcharhiniform sharks. These s tudies reveal that sharks are generally asynchronous opportunistic feeders on the most abundant prey item, which are primarily other fishes. Studies o f natural feeding behavior are few and many observations of feeding behavio r are based on anecdotal reports. To capture their prey sharks either ram, suction, bite, filter, or use a combination of these behaviors. Foraging ma y be solitary or aggregate, and while cooperative foraging has been hypothe sized it has not been conclusively demonstrated. Studies on the anatomy of the feeding mechanism are abundant and thorough, and far exceed the number of functional studies. Many of these studies have investigated the function al role of morphological features such as the protrusible upper jaw, but on ly recently have we begun to interpret the mechanics of the feeding apparat us and how it affects feeding behavior. Teeth are represented in the fossil record and are readily available in extant sharks. Therefore much is known about their morphology but again functional studies are primarily theoreti cal and await experimental analysis. Recent mechanistic approaches to the s tudy of prey capture have revealed that kinematic and motor patterns are co nserved in many species and that the ability to modulate feeding behavior v aries greatly among taxa. In addition, the relationship of jaw suspension t o feeding behavior is not as clear as was once believed, and contrary to pr evious interpretations upper jaw protrusibility appears to be related to th e morphology of the upper jaw-chondrocranial articulation rather than the t ype of jaw suspension. Finally, we propose a set of specific hypotheses inc luding: (1) The functional specialization for suction feeding hypothesis th at morphological and functional specialization for suction feeding has repe atedly arisen in numerous elasmobranch lineages, (2) The aquatic suction fe eding functional convergence hypothesis that similar hydrodynamic constrain ts in bony fishes and sharks result in convergent morphological and functio nal specializations for suction feeding in both groups, (3) The feeding mod ulation hypothesis that suction capture events in sharks are more stereotyp ed and therefore less modulated compared to ram and bite capture events, an d (4) The independence of jaw suspension and feeding behavior hypothesis wh ereby the traditional categorization of jaw suspension types in sharks is n ot a good predictor of jaw mobility and prey capture behavior. Together wit h a set of questions these hypotheses help to guide future research on the feeding biology of sharks.