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 video-recorded feeding sequences. To determine what happens to the baleen during gape closure, 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 that the balaenid 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. The internal horn tubes have greater external and hollow luminal diameter but lower density in the lateral relative to medial baleen of bowhead and fin whales, suggesting a greater capacity for lateral bending. Baleen bending has major consequences not only for feeding morphology and energetics but also for conservation given that entanglement in fishing gear is a leading cause of whale mortality.
FOOTNOTES
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: A.J.W.; Methodology: A.J.W., D.R., M.V.R., M.J.M., T.L.S.; Software: A.J.W., M.V.R.; Validation: A.J.W., M.J.M., T.L.S.; Formal analysis: A.J.W., M.J.M., T.L.S.; Investigation: A.J.W., D.R., M.V.R., M.J.M., T.L.S.; Resources: A.J.W., D.R., M.V.R., M.J.M., T.L.S.; Data curation: A.J.W., D.R., T.L.S.; Writing - original draft: A.J.W.; Writing - review & editing: A.J.W., D.R., M.V.R., M.J.M., T.L.S.; Visualization: A.J.W., D.R., M.V.R., T.L.S.; Supervision: A.J.W.; Project administration: A.J.W., T.L.S.; Funding acquisition: A.J.W., T.L.S.
Funding
Funding for A.J.W. came from Hampden-Sydney College faculty grants and a Harris Award from the Virginia Foundation for Independent Colleges. National Oceanic and Atmospheric Administration CINAR Award NA14OAR4320158 and North Slope Borough, Alaska, funded OHMSETT testing.
Data availability
All data are freely available in the Dryad Digital Repository (Werth et al., 2018): dryad.73rm81p.
- Received July 23, 2018.
- Accepted October 11, 2018.
- © 2018. Published by The Company of Biologists Ltd
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