Feeding anatomy,filter-feeding rate,and diet of whale sharks Rhincodon typus during surface ram filter feeding off the Yucatan Peninsula,Mexico |
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Authors: | Philip J. Motta Michael Maslanka Robert E. Hueter Ray L. Davis Rafael de la Parra Samantha L. Mulvany Maria Laura Habegger James A. Strother Kyle R. Mara Jayne M. Gardiner John P. Tyminski Leslie D. Zeigler |
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Affiliation: | 1. Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas, Av. IPN s/n, 23096 La Paz, BCS, Mexico;2. Unidad Académica Mazatlán, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Mazatlán, Sinaloa 82040, Mexico;3. Department of Veterinary Medicine, University of Alaska, Fairbanks, Fairbanks, AK 99775-7000, United States;4. Asociación de Pesca Deportiva y Ecoturismo de Bahía de los Ángeles, Domicilio conocido Bahía de los Ángeles, Baja California 22980, Mexico;5. Miembro de El Colegio de Sinaloa, Antonio Rosales 435 Poniente, Culiacán, Sinaloa, Mexico |
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Abstract: | The feeding anatomy, behavior and diet of the whale shark Rhincodon typus were studied off Cabo Catoche, Yucatan Peninsula, Mexico. The filtering apparatus is composed of 20 unique filtering pads that completely occlude the pharyngeal cavity. A reticulated mesh lies on the proximal surface of the pads, with openings averaging 1.2 mm in diameter. Superficial to this, a series of primary and secondary cartilaginous vanes support the pads and direct the water across the primary gill filaments. During surface ram filter feeding, sharks swam at an average velocity of 1.1 m/s with 85% of the open mouth below the water's surface. Sharks on average spent approximately 7.5 h/day feeding at the surface on dense plankton dominated by sergestids, calanoid copepods, chaetognaths and fish larvae. Based on calculated flow speed and underwater mouth area, it was estimated that a whale shark of 443 cm total length (TL) filters 326 m3/h, and a 622 cm TL shark 614 m3/h. With an average plankton biomass of 4.5 g/m3 at the feeding site, the two sizes of sharks on average would ingest 1467 and 2763 g of plankton per hour, and their daily ration would be approximately 14,931 and 28,121 kJ, respectively. These values are consistent with independently derived feeding rations of captive, growing whale sharks in an aquarium. A feeding mechanism utilizing cross-flow filtration of plankton is described, allowing the sharks to ingest plankton that is smaller than the mesh while reducing clogging of the filtering apparatus. |
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