Putative Mating Behavior in Basking Sharks off the Nova Scotia Coast

We report aerial observation of 13 basking sharks (Cetorhinus maximus) engaged in putative mating behavior near the ocean surface 21 June 1998 at approximately 1230 AST, 140.8 km from the Nova Scotia mainland in the North Atlantic at 44?16'N, 61038'W, depth 130 m. Video and photo documentation showed the 68 m long sharks, some with discrete white patches on the dorsum and appendages, swimming slowly clockwise in a tight circle with many animals closely associated with up to three other animals. Previously described behaviors and motor patterns consistent with elasmobranch reproduction including "parallel swimming," possible "pectoral biting," "nudging," and "male on top of female" were seen as well as other behaviors, including nose-to-tail following; flank approach; close approach involving rostral contact or proximity with the gill, pectoral fin, vent, and dorsum; and echelon swimming. Behaviors involving close and persistent physical association of two or more animals and the persistence of the circling behavior in a circumscribed area over a period in excess of 5 min indicated that this may represent the first well-documented observation of group courtship behavior in basking sharks.