Thresher sharks use their huge tails to pursue and immobilise their prey during feeding, confirms a recent study based on video evidence.
The results of this study by Scott Aalbers, Diego Bernal and Chugey Sepulveda are published in a recent issue of the Journal of Fish Biology.
It has long been suspected that the very long caudal fins of thresher sharks (Alopias spp.) are not only used for generating thrust during swimming, but also have a role to play in feeding, as evidenced by the frequent hooking of thresher sharks in the tail using long-line gear.
The authors towed an underwater video camera behind a boat in the nearshore waters of southern California. Two lines baited with live chub mackerel (Scomber japonicus) were towed behind the rearwards-facing camera and situated almost directly in front of the camera lens.
Over 27 days, the authors collected 650 minutes of digital video that included footage from 33 individual common thresher sharks (Alopias vulpinus).
The authors observed 14 of these 33 sharks attempting to strike the bait with their tails, successfully hitting them 65% of the time.
The sharks used two methods to achieve the strike: in the first method, they rapidly surged forward, undulating their bodies. This created a backwards-moving wave down their bodies that ended with a flick of the tail (this was the predominant method observed 17 times with a success rate of 47%).
The second method had the shark swimming next to the bait and striking it with a lateral flick of the tail (this was observed 12 times with a success rate of 92%).
For more information, see the paper: Aalbers, SA, D Bernal and CA Sepulveda (2010) The functional role of the caudal fin in the feeding ecology of the common thresher shark Alopias vulpinus. Journal of Fish Biology 76, pp. 1863–1868.