Surface foraging behaviour of the North Atlantic right whale, Eubalaena glacialis, and associated zooplankton characteristics

Abstract

Right whales in Cape Cod Bay, Massachusetts, were studied to determine the relationship between their surface feeding behaviour and the density and composition of their planktonic prey. The swimming path characteristics of whales feeding, socializing, and travelling were compared. Zooplankton samples collected in the feeding path were contrasted with those from areas where whales were not present. Surface prey patches where right whales fed were dominated by Calanus finmarchicus (21 samples), Pseudocalanus minutus (n = 13), Centropages sp. (n = 3), and larval barnacles (n = 2). The zooplankton density in the feeding path of the whales tested significantly higher (Mann–Whitney U-test, P < 0.001) than at stations where whales were not present (mean total densities were 6.54 × 103 (SE = 1.03 × 103) and 0.87 × 103 (SE = 0.19 × 103) organisms/m3, respectively). Feeding was rarely observed in locations where the total zooplankton density was less than 1000 organisms/m3. The rate of change of direction in the feeding path (mean 19.3°/10 m of path) was significantly higher (P < 0.001) than for paths of whales travelling (mean 5.3°/10 m of path), reflecting area-restricted foraging behaviour.

Adaptations of the cetacean hyolingual apparatus for aquatic feeding and thermoregulation

“…In contrast to balaenopterids, balaenids are slow, rotund cruisers that filter a constant current of water through a mat of long, finely fringed baleen to skim dense swarms of tiny zooplankton (Watkins and Schevill, 1979;Lowry and Frost, 1984;Mayo and Marx, 1990;Lambertsen et al, 2005). Water enters through a large cranial cleft, the subrostral gap, between left and right baleen racks, flows through the oral cavity over the tongue, then flows laterally between baleen plates and passes out a gutter-like groove or depression, the orolabial sulcus, at the rear of the lower lip.…”

“…A second mechanical hypothesis depends on observations of Southern right whales shaking or ''flapping'' lips between filtering bouts to indirectly dis-lodge prey. Right whale ''nodding'' behavior (Mayo and Marx, 1990) suggests a third possibility of hydrodynamic reverse-flow ''backwash'' by means of brief re-entry of water into the mouth. Rapid tongue depression coupled with jaw abduction and perhaps outward rotation could create sufficient negative pressure to draw cleansing water in.…”

Structure of the integument of southern right whales, Eubalaena australis

“…Distinct nerve nets and blood sinus appendages have been associated with these hairs in bowhead whales (Haldiman et al, 1981(Haldiman et al, , 1985Haldiman and Tarpley, 1993) and may indicate a tactile function. The number, spacing, and distribution of these hairs on the snout and chin of southern right whales would seem to support such a function, possibly allowing rapid detection of changes in prey density and, thus, enabling the whale to stay within the densest part of the swarm (North Atlantic right whales, Mayo and Marx, 1990).…”

Physical processes and zooplankton distribution in the Great South Channel : observational and numerical studies

“…The primary food of the North Atlantic right whale, Eubalaena glacialis, is the copepod Calanus finmarchicus (Matthews, 1938;Tomlin, 1957;Omura et al, 1969;Nemoto, 1970;Schevil, 1976, 1979;Scott et al, 1985;Kenney et al , 1986;Gaskin, 1987Gaskin, , 1991Wishner et al, 1988;Murison and Gaskin, 1989;Mayo and Marx, 1990). This copepod overwinters in a dormant stage (primarily copepodite V) throughout the western Gulf of Maine, especially in the deep basins, and matures and reproduces in early spring.…”

“…The young develop through the onset of the seasonal thermocline and the spring phytoplankton bloom into late-stage copepodites and adults by late spring. Right whales feed by swimming with their mouths open, u sing their baleen to filter prey out of the water (Nemoto, 1970;Schevill, 1976, 1979;Pivorunas, 1979;Mayo and Marx, 1990). This process requires more energy than the whale would expend by swimming with its mouth closed, because of the additional drag.…”