ABSTRACT
Animal-borne video recordings from blue whales in the open ocean show that remoras preferentially adhere to specific regions on the surface of the whale. Using empirical and computational fluid dynamics analyses, we show that remora attachment was specific to regions of separating flow and wakes caused by surface features on the whale. Adhesion at these locations offers remoras drag reduction of up to 71–84% compared with the freestream. Remoras were observed to move freely along the surface of the whale using skimming and sliding behaviors. Skimming provided drag reduction as high as 50–72% at some locations for some remora sizes, but little to none was available in regions where few to no remoras were observed. Experimental work suggests that the Venturi effect may help remoras stay near the whale while skimming. Understanding the flow environment around a swimming blue whale will inform the placement of biosensor tags to increase attachment time for extended ecological monitoring.
Footnotes
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: B.E.F.; Methodology: B.E.F., S.M., O.L., E.J.A., D.E.C., J.C., A.S.F., J.A.G.; Software: G.H., M.V., D.E.C. Formal analysis: B.E.F., S.M., O.L., E.J.A., A.M., D.E.C. Investigation: B.E.F., S.M., O.L., E.J.A., M.B., J.H.N.; Resources: O.L., E.J.A., G.H., M.V., J.C., A.S.F., J.A.G.; Data curation: D.E.C., H.E.A.; Writing - original draft: B.E.F., S.M.; Writing - review & editing: B.E.F., S.M., O.L., E.J.A., D.E.C., M.B., J.H.N., H.E.A., J.C., A.S.F., J.A.G.; Visualization: B.E.F., O.L., E.J.A., A.M.; Supervision: B.E.F.; Project administration: B.E.F.; Funding acquisition: B.E.F., S.M., E.J.A., J.A.G.
Funding
Financial support was provided by Stanford University and a Terman Fellowship to J.A.G., the Ministerio de Economía y Competitividad, Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain (ref. TRA2017-88508-R) to O.L., a grant from the Grove City College Swezey Fund to E.J.A., and New Jersey Institute of Technology to B.E.F. Additional support for tagging and filming operations came from the National Oceanic and Atmospheric Administration (NOAA) and the BBC. The Barcelona Supercomputing Center awarded access to the MareNostrum IV machine (Barcelona, Spain).
Supplementary information
Supplementary information available online at https://jeb.biologists.org/lookup/doi/10.1242/jeb.226654.supplemental
- Received April 9, 2020.
- Accepted September 7, 2020.
- © 2020. Published by The Company of Biologists Ltd
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