Fish, F.E. 1998. Comparative Kinematics and Hydrodynamics of Odontocete Cetaceans: Morphological and Ecological Correlates with Swimming Performance. J. Exp. Biol. 201:2867-2877.

Presented by: Cherie Jenkins and Jason Bishop

The purpose of this study was to compare the swimming kinematics (the mechanics of motion) of various cetacean species displaying diverse morphologies.

To do this, the propulsive morphology and swimming performance of four types of odontocete cetaceans were compared:

1. Bottlenose Dolphin (Tursiops truncates)-have a sleek, streamlined fusiform body with a sweptback dorsal fin, medium sized flippers that are rounded at the tips and a long rostrum. The range from 7-13 ft.
2. Killer whale (Orcinus orca) has a sleek, streamlined body with large rounded flippers, a moderately sweptback dorsal fin and a short rostrum. They range in size from 15-30 ft.
3. Beluga whale (Delphinapterus leucas) has an elongated fusiform body but it is robust and stocky. They have small paddle-like flippers, no dorsal fin and a short rostrum. They also have skin with think folds of blubber. They range in size from 10-18 ft.
4. False Killer whale (Pseudorca crassidens) has and elongated body with a highly sweptback dorsal fin, flippers that taper to a point and a short rostrum. They range from 11-20 ft.

It was expected that cetaceans possessing morphological characteristics that would help to reduce drag and enhance thrust production would demonstrate increased swimming performance.

Large differences exist between the morphologies and behavioral ecologies of cetaceans; corresponding differences in swimming characteristics are therefore expected between species.

Those cetaceans that are active predators and need to catch their prey would need to be able to swim at higher speeds. T. truncatus are active predators that eat a wide variety of fish and squid. O. orcas are also active predators and are the top predators in the ocean. They eat fish, squid, penguins, and some marine mammals. P. crassidens also eat fish and on rare occasions even dolphins.

Delphinapterus leucas would not need the speed of the others. They forage at or near the bottom of shallow water. They are known to prey on about 100 different kinds of primarily bottom dwelling animals.

To test the predictions of the association between morphological design and swimming performance, measurements of the motions of the cetaceans were taken while swimming to compute trust power, propulsive efficiency and drag characteristics over a variety of swimming speeds.

Dolphins use the movement of their caudal tailstock and flukes for propulsion. The fluke has a thunniform shape, which is a lunate tail. This is the best shape for fast swimming.

Tail beat frequency (1 cycle or tail beat per second) was measured as a function of length specific velocity (body lengths / sec). It was found that as velocity increased, so did the frequency of the propulsive cycle. This means that the faster the whale swam, the faster its tail was beating. The tail beat frequency increased the fastest (largest slope) for D. leucas, then P. crassidens, T. truncatus, and O. orca.

The maximum angle of pitch in degrees was measured vs. length specific velocity. Unlike the tail beat frequency, which measured the movement of the whole tail, the angle of pitch measures just the angle of fluke movement, shown as the angle CDE. It was shown that there was a linear decrease in pitch angle as velocity increased.

D. leucas showed the largest decreasing slope. A steeply decreasing slope means that as velocity increased, the tail beat in a straighter line.

T. truncatus had the shallowest slope. A shallow slope meant that although the angle did decrease, it took a higher velocity to do it.

The whales showed minimum values of propulsive efficiency at swimming speed less than 0.5 L/s. As velocity increased, so did the efficiency until it reached a maximum. At higher speeds, it either remained at the maximum efficiency or it eventually decreased.

P. crassidens exhibited the highest propulsive efficiency followed by O. orca , T. truncatus and D. leucas. D. leucas was relatively consistent over the minimum efficiency rate within 1.5 % of the maximum. The maximum efficiency of the fluke’s propulsion occurs near their cruising speeds. This would be beneficial in reducing energy costs during transit between widely dispersed feeding sites or during migration.

The differences in CDd (coefficient of drag corrected for depth) are consistent with variations in the morphology affecting swimming performance. D. leucas had a high CDd. It has a bulbous rounded head, which would increase drag. In addition the folds of fat along the body would also increase drag. The other three whales had lower CDd. They have tighter skin and a smoother body contour.

The minimum CDd for all the species occurred at or close to the maximum speeds measured in the study and above normal cruising speeds. This reduced drag at higher velocities would help in burst swimming and would especially aid cetaceans, which feed on large and rapidly swimming prey. A higher CDd can be tolerated by D. leucas who feeds on slower moving prey.

The design of the flukes in conjunction with the morphology of the body was the major determinants of swimming speed. The flukes of cetaceans provide a high propulsive efficiency of 75-90% that surpasses most manufactured propellers which only average 70% efficiency. The magnitude of the efficiency was dependent on the design of the flukes with the Aspect Ratio being the most important morphological variable. Aspect Ratio (AR) was measured as the fluke span squared / fluke area. A high AR and tapering of the flukes reduces drag while maximizing thrust. The wider the fluke from left to right and the thinner from front to back, the higher the AR. P. crassidens had the highest AR and the highest maximum efficiency and was one of the faster swimmers. D. leucas had the lowest fluke AR and the lowest maximum propulsive efficiency and was the slowest swimmer.

Other Factors Affecting Overall Swimming Performance

• Phylogenetics (D. leucas is a member of the family Monodontidae, where the others are in the family Delphinidae)
• Foraging behaviors (solitary vs. use of coordinated hunts)
• Prey size and abundance
• Social behavior
• Sexual dimorphism
• Habitat (packed ice vs. open ocean)
• Maneuverability

Carwardine, Mark, et al. Whales Dolphins and Porpoises. San Francisco,

US Weldon Owen Inc., 1998.

Coffey, David J. Dolphins Whales and Porpoises. New York: MacMillian

Publishing Co. Inc., 1977.

 Curren, K.C., N. Bose and J. Lien. "Swimming Kinematics of a Harbor Poroise and an Atlantic White-sided Dolphin." Marine Mammal Science 10 (1994): 485-492.

Fish, Frank E. "Transitions from Drag-based Swimming to Lift-based Propulsion in Mammalian Swimming." American Zoology 36 (1996): 628-641.

Pabst, D. Ann. "Springs in Swimming Animals." American Zoology 36 (1996): 723-735.