Meeting Abstract
P2.118 Monday, Jan. 5 The role of the caudal fin in the feeding ecology of the common thresher shark (Alopias vulpinus) SEPULVEDA, C.A.*; AALBERS, S.A.; DONLEY, J.M.; SYME, D.A.; BERNAL, D.; Pfleger institute of Environmental Research (PIER), Oceanside CA; PIER; MiraCosta College; Univ. of Calgary, Canada; Univ. of Massachusetts, Dartmouth chugey@pier.org
The thresher sharks (Alopiidae) comprise a monophyletic group of pelagic sharks most commonly recognized by their elongate upper lobe of the caudal fin. It has been hypothesized that thresher sharks utilize the elongate fin to stun small-schooling prey while feeding. The bi-functional role of the caudal fin for both thrust production and predation represents a unique adaptation that has not been described for any elasmobranch species. Despite the commercial importance of the thresher sharks, there are no published accounts on how the caudal fin is used during feeding. Field and laboratory studies were conducted to 1) acquire video recordings of feeding common threshers in the wild, 2) examine the caudal fin morphology and 3) investigate the ocular morphology which enables vision in the posterior field. Of the 140 specimens captured and released (2005-2008), only 4 sharks were hooked in the mouth while the remainder (97%) were hooked in the caudal fin. Video records of thresher sharks feeding in the wild yielded footage from 20 individual caudal fin-feeding events. Morphological examination of the common thresher caudal fin revealed that the upper lobe is predominantly comprised of tendinous and cartilaginous support tissues. The dissections also revealed the presence of both aerobic (red) and anaerobic (white) muscle fibers throughout the entire length of the caudal fin. In general, the caudal fin structural architecture appears to be similar to that described for lamnid sharks, but with much larger dorso-ventral cartilaginous support elements. Preliminary findings also show that the eye has the capacity to rotate along the longitudinal axis in an anterior-posterior direction within the orbit which may enhance vision in the posterior field.
