Like other baleen whales, North Atlantic right whales are filter feeders, using their remarkable baleen to strain prey from the water. Baleen is made of keratin, the same material that makes up our hair and fingernails. It hangs like a curtain in a series of plates on either side of the whale's upper jaw with more than 200 plates per side, between 2 and 2.8 m in length. On the inner edge of each plate is a hair-like fringe. As the whale swims through a prey patch with its mouth wide open, water streams out between the plates, but the matted fringe traps the prey which is then brushed off with the tongue and swallowed.

Right whale calf in the Bay of Fundy showing
the opening by which the seawater enters before
going through the baleen.
North Atlantic right whales feed on zooplankton, primarily the calanoid copepod Calanus finmarchicus, whose size is roughly that of a grain of rice. It is believed that right whales need to consume between 407,000 and 4,140,000 calories every day 1, so they must find extremely dense patches of zooplankton on which to feed since it has to be worth their while to open those immense mouths. From a human perspective, the daily caloric requirement of a right whale is equivalent to that of 203 to 2,070 people. Tides and other currents can create high concentrations of zooplankton, and in Cape Cod Bay for example right whales feed on patches with a minimum concentration of 4,000 organisms per cubic meter of water. This amount of food allows right whales to maintain a mass 50 billion times larger than that of a large copepod. Right whales also have the ability to store energy in their blubber or fat layer which is up to 20 cm thick.

Right whales use different foraging strategies depending on the distribution of zooplankton in the water column. When the zooplankton is at or near the surface, the whale swims steadily at about 5 km/h (3 knots) through the patch with its mouth open, changing course to remain within the densest feeding area.
Left side of a skim feeding right whale in the
Great South Channel Critical Habitat. The white
gum line and grey baleen are visible below the
edge of the upper jaw.
If the prey is concentrated at the surface the whale "skim-feeds", swimming with its upper jaw held high above the water. When patches form a little deeper, the whale will "sub-surface feed", coming up every 25 minutes or so to breathe. In both cases the mouth remains open except when the baleen is "flushed" - the action by which the whale brushes the zooplankton off the baleen with its tongue - about once per hour 2. Skim and sub-surface feeding are often seen in Cape Cod Bay and the Great South Channel. In the Bay of Fundy the calanoid copepods are concentrated near the seafloor at depths of 100 m to more than 200 m and right whales must dive to the bottom to feed. These dives can last up to 20 minutes and whales sometimes surface with mud on their heads indicating they have been all the way to the bottom (200+ m).

High concentrations of copepods have been found in the spring, summer and fall in all known right whale habitats: lower Bay of Fundy 3, Roseway Basin 4, Great South Channel 5 and Cape Cod Bay 6. However, no concentrations of plankton have been documented in the calving ground in the southeast United States, suggesting right whales are not feeding in that habitat.

1 Kenney, R. D., M. A. M. Hyman, R. E. Owen, G. P. Scott, and H. E. Winn. 1986. Estimation of prey densities required by western North Atlantic right whales. Marine Mammal Science 2:1-13.

2, 6 Mayo, C. A., and M. K. Marx. 1990. Surface foraging behaviour of the North Atlantic right whale, Eubalaena glacialis, and associated zooplankton characteristics. Canadian Journal of Zoology 68:2214-2220.

3 Murison, L. D., and D. E. Gaskin. 1989. Zooplankton distributions and feeding ecology of right whales (Eubalaena glacialis glacialis) in the outer Bay of Fundy, Canada. M.S. Thesis. University of Guelph, Guelph, Ontario, Canada.

4 Baumgartner, M. F., and B. R. Mate. 2003. Summertime foraging ecology of North Atlantic right whales. Marine Ecology Progress Series 264:123-135.

5 Wishner, K. F., J. R. Schoenherr, R. Beardsley, and C. Chen. 1995. Abundance, distribution and population structure of the copepod Calanus finmarchicus in a springtime right whale feeding area in the south western Gulf of Maine. Continental Shelf Research 15:475-507.

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