Heterocercal tail function in leopard sharks: a three-dimensional kinematic analysis of two models

Two different models have been proposed to explain the function of the heterocercal tail in shark locomotion. The classical model proposes that, as a result of lift generated by the tail as it beats, the net force acting on the tail is directed dorsally and anteriorly. In contrast, Thomson's model suggests that the tail generates a net force directed through the shark's center of gravity, i.e. ventrally and anteriorly. In this study, we evaluate these two models by describing the three-dimensional kinematics of the heterocercal tail in the leopard shark Triakis semifasciata during swimming. Lateral and posterior views of the tail were examined from four individuals swimming in a flow tank at 1.2 L s-1 (where L is total length) using two high-speed video cameras filming simultaneously at 250 fields s-1. These two simultaneous views allowed eight landmarks on the tail to be followed in three dimensions through time. These landmarks allowed the tail to be divided into separate surfaces whose orientation over time was calculated. Points located anteriorly on the tail go through significantly smaller excursions and reach their maximum lateral excursion significantly earlier in the beat cycle than points on the trailing edge of the tail. Three-dimensional angle calculations show that the terminal lobe leads the ventral lobe through a beat, as predicted by the classical model. Dye-stream visualizations confirmed that this pattern of movement deflects water ventrally and posteriorly to the moving tail, providing strong support for the classical model. Additionally, our results show that a three-dimensional analysis is critical to understanding the function of the heterocercal tail.

[1]  Lauder,et al.  Are muscle fibers within fish myotomes activated synchronously? Patterns of recruitment within deep myomeric musculature during swimming in largemouth bass , 1995, The Journal of experimental biology.

[2]  P. Webb THE EFFECT OF SOLID AND POROUS CHANNEL WALLS ON STEADY SWIMMING OF STEELHEAD TROUT ONCORHYNCHUS MYKISS , 1993 .

[3]  J. Videler Fish Swimming , 1993, Springer Netherlands.

[4]  Jy Ma,et al.  Tendon structure of the Caudal Fin in the Blue Sharkd, Prionace glauca , 1992 .

[5]  C. Mcgowan Dinosaurs, spitfires, and sea dragons , 1991 .

[6]  George V. Lauder,et al.  Caudal fin locomotion in ray-finned fishes: historical and functional analyses , 1989 .

[7]  T. Hung Life in Moving Fluids—The physical biology of flow , 1988 .

[8]  Robert L. Carroll,et al.  Vertebrate Paleontology and Evolution , 1988 .

[9]  C. Ellington The Aerodynamics of Hovering Insect Flight. II. Morphological Parameters , 1984 .

[10]  C. Ellington The Aerodynamics of Hovering Insect Flight. III. Kinematics , 1984 .

[11]  Paul W. Webb,et al.  Function of the Caudal Fin in Early Fishes , 1980 .

[12]  Keith Stewart Thomson,et al.  Body Form and Locomotion in Sharks , 1977 .

[13]  Keith Stewart Thomson,et al.  On the heterocercal tail in sharks , 1976, Paleobiology.

[14]  P. Webb Hydrodynamics and Energetics of Fish Propulsion , 1975 .

[15]  J. Hopson The functional significance of the hypocercal tail and lateral fin fold of Anaspid ostracoderms / James A. Hopson --. , 1974 .

[16]  J. Videler,et al.  On the interrelationships between morphology and movement in the tail of cichlid fish Tilapia nilotica (L.). , 1974 .

[17]  P. Webb Effects of Partial Caudal-Fin Amputation on the Kinematics and Metabolic Rate of Underyearling Sockeye Salmon (Oncorhynchus Nerka) At Steady Swimming Speeds , 1973 .

[18]  W. A. Gosline,et al.  Functional Morphology and Classification of Teleostean Fishes , 1971 .

[19]  J. R. Simons The Direction of the Thrust Produced by the Heterocercal Tails of Two Dissimilar Elasmobranchs: The Port Jackson Shark, Heterodontus Portusjacksoni (Meyer), and the Piked Dogfish, Squalus Megalops (Macleay) , 1970 .

[20]  Iu G Aleev,et al.  Function and gross morphology in fish , 1969 .

[21]  R. Alexander,et al.  THE LIFT PRODUCED BY THE HETEROCERCAL TAILS OF SELACHII , 1965 .

[22]  R. Bainbridge,et al.  Caudal Fin and Body Movement in the Propulsion of some Fish , 1963 .

[23]  XXIV.—A mechanical investigation into the effectual action of the caudal fin of some aquatic chordates , 1936 .