Functional morphology of the mouth of the bowhead whale and its implications for conservation

Abstract

Bowhead whales (Balaena mysticetus) hauled out on shore-fast ice by Inupiat whale hunters off Barrow, Alaska were examined. Anatomical observations confirmed the occurrence of a large, well-muscled tongue. Temporomandibular articulations were synovial. The mandibular symphysis was unfused. Standard measurement of baleen plates and close-range photogrammetry of a baleen rack confirmed that the anterior portion of the baleen rack is strongly convex, in contrast to its shape in balaenopterids. Moderate force applied to the lower lip in a lateral direction caused a pronounced abduction of the lower jaw. These observations support a conclusion that during feeding, the tongue may deflect the incoming flow of prey-laden water from side to side in the mouth, to convey prey slurries into the postlingual recess. Abduction of the lower lip likely would establish a channel for acceleration of flow around the outside of the baleen racks, reducing external pressures and drawing water out through the baleen. Thus, the shape of the baleen rack in the bowhead appears to be an adaptation to reduce the amplitude of the bow wave projected during feeding, the simultaneous advantage being concentration of prey slurries inside the mouth. It may also impart a configuration to the bow wave that stimulates countereffective evasive effort by actively mobile prey. Final compaction of a concentrated prey slurry in the postlingual recess probably involves retraction of the tongue against the oropharyngeal wall. These insights notably enable consideration of certain threats to bowheads and right whales (Balaenidae) associated with oil spills and oral entanglement. Previous research on the "physiologic" effects of fouling of baleen with oil is judged to be inadequate with respect to this taxonomic family. Oral entanglement with non biodegradable marine debris is predicted to be lethal because of interference with a critical hydrostatic oral seal. © 2005 American Society of Mammalogists.