How do baleen whales stow their filter? A comparative biomechanical analysis of baleen bending

Author:

Werth Alexander J.1ORCID,Rita Diego2,Rosario Michael V.3,Moore Michael J.4,Sformo Todd L.56

Affiliation:

1. Department of Biology, Hampden-Sydney College, Hampden-Sydney VA 23943, USA

2. Department of Evolutionary Biology, Ecology, and Environmental Science, University of Barcelona, 08028 Barcelona Spain

3. Department of Ecology & Evolutionary Biology, Brown University, Providence RI 02912, USA; current address Department of Biology, West Chester University, West Chester PA 19383, USA

4. Biology Department, Woods Hole Oceanographic Institution, Woods Hole MA 02543, USA

5. Department of Wildlife Management, North Slope Borough, Barrow AK 99723, USA

6. Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks AK 99775, USA

Abstract

Bowhead and right whale (balaenid) baleen filtering plates, longer in vertical dimension (3-4+ m) than the closed mouth, presumably bend during gape closure. This has not been observed in live whales, even with scrutiny of videorecorded feeding sequences. To determine what happens to baleen as gape closes, we conducted an integrative, multifactorial study including materials testing, functional (flow tank and kinematic) testing, and histological examination. We measured baleen bending properties along the dorsoventral length of plates and anteroposterior location within a rack of plates via mechanical (axial bending, composite flexure, compression, and tension) tests of hydrated and air-dried tissue samples from balaenid and other whale baleen. Balaenid baleen is remarkably strong yet pliable, with ductile fringes and low stiffness and high elasticity when wet; it likely bends in the closed mouth when not used for filtration. Calculation of flexural modulus from stress/strain experiments shows baleen is slightly more flexible where it emerges from the gums and at its ventral terminus, but kinematic analysis indicates plates bend evenly along their whole length. Fin and humpback whale baleen has similar material properties but less flexibility, with no dorsoventral variation. Internal horn tubes have greater external and hollow luminal diameter but lower density in lateral relative to medial baleen of bowhead and fin whales, suggesting greater capacity for lateral bending. Baleen bending has major consequences not only for feeding morphology and energetics but also conservation given that entanglement in fishing gear is a leading cause of whale mortality.

Funder

National Oceanic and Atmospheric Administration

Publisher

The Company of Biologists

Subject

Insect Science,Molecular Biology,Animal Science and Zoology,Aquatic Science,Physiology,Ecology, Evolution, Behavior and Systematics

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