Coping with copepods: do right whales (Eubalaena glacialis) forage visually in dark waters?

• Published in: Philosophical transactions of the Royal Society of London. Series B. Biological sciences 2017-04, Vol.372 (1717), p.1-8
• Main Authors: Cronin, Thomas W., Fasick, Jeffry I., Schweikert, Lorian E., Johnsen, Sönke, Kezmoh, Lorren J., Baumgartner, Mark F.
• Format: Article
• Language: English
• ISSN: 0962-8436

North Atlantic right whales (Eubalaena glacialis) feed during the spring an early summer in marine waters off the northeast coast of North America. Their food primarily consists of planktonic copepods, Calanus finmarchicus which they consume in large numbers by ram filter feeding. The coastal waters where these whales forage are turbid, but they successfully locate copepod swarms during the day at depths exceeding 100 m, where light is very dim and copepod patches may be difficult to see. Using models of E. glacialis visual sensitivity together with measurements of light in waters near Cape Cod where they feed and of light attenuation by living copepods in seawater, we evaluated the potential for visual foraging by these whales. Our results suggest that vision may be useful for finding copepod patches, particularly if E. glacialis searches overhead for silhouetted masses or layers of copepods. This should permit the whales to locate C. finmarchicus visually throughout most daylight hours at depths throughout their foraging range. Looking laterally, the whales might also be able to see copepod patches at short range near the surface. This article is part of the themed issue 'Vision in dim light'.