Hydrodynamic performance of the flippers of large-bodied cetaceans in relation to locomotor ecology

Cetaceans evolved flippers that are unique in both size and shape probably due to selection pressures associated with foraging and body size. Flippers function as control surfaces for maneuverability and stability. Flippers of cetaceans and engineered hydrofoils are similar with streamlined cross-sections and wing-like planforms, which affect lift, drag and hydrodynamic efficiency. Scale models of the flippers from large-bodied (body length >6 m) cetaceans (fin whale, killer whale, sperm whale) were constructed from computed tomography (CT) scans of flippers. Flipper planforms were highly tapered for the fin whale, a rounded, paddle-like design for the killer whale, and a square geometry for the sperm whale. Hydrodynamic properties of the models at varying angles of attack (–40o to 40) were determined in a water tunnel with a multi-axis load cell. The flippers were found to have hydrodynamic characteristics similar to engineered wings. Differences in flipper morphology of large-bodied cetaceans and their hydrodynamic performance are associated with the requirements of aquatic locomotion involved with ecology of the whales. The flippers of the killer whale provided the greatest maneuverability, whereas the flippers of the fin whale had low drag for lunging and the flippers of the sperm whale provided lift for diving.