Pygmy Right Whales (Neobalaenidae)

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Pygmy right whales

(Neobalaenidae)

Class Mammalia

Order Cetacea

Suborder Mysticeti

Family Neobalaenidae

Thumbnail description
Smallest baleen whale, with sickle-shaped dorsal fin, arched rostrum, inconspicuous blow, and coloration ranging from black or gray above to pale below

Size
16.4–21.3 ft (5–6.5 m); maximum weight is 7,562 lb (3,430 kg)

Number of genera, species
1 genera; 1 species

Habitat
Coastal and pelagic waters of the Southern Hemisphere, 31–52° S of the equator

Conservation status
Not listed by the IUCN

Distribution
Circumpolar, from about 30–55° S of the equator

Evolution and systematics

The pygmy right whale, Caperea marginata, is the smallest baleen whale and the only member of family Neobalaenidae. In the past, it was placed among the right and bowhead whales (Balaenidae). It is now considered to be a closer relative to the rorquals (Balaenopteridae) and gray whales (Eschrichtiidae). DNA research from 1992 and 1993 by Úlfur Árnason and colleagues, as well as morphological evidence, have supported its membership in a separate family.

Caperea marginata differs from other right whales in having a proportionally smaller head and humerus, a different type of baleen, a dorsal fin, four digits instead of five, and 44 or fewer vertebrae. The skull is also very different from those of the Balaenidae. The occipital shield is larger, and projects farther to the fore. The rostrum is shorter, wider, and although it forms less of an arch, the arch becomes more pronounced with age. The supraorbital processes are shorter. The nasal bones are smaller. The glenoid fossae and the orbits are less ventrally placed than on the Balaenidae.

No studies of geographic variation have been conducted, and there are no recognized subspecies. No fossils are known.

The taxonomy for this species is Caperea marginata (Gray, 1846), temperate waters of the Southern Hemisphere.

Caperea marginata is streamlined. Adults are heftier than rorquals but not as wide as bowhead or right whales. The relatively large head comprises about one-fourth of total length. The jawline arches and then reverses direction just northwest of the eye, somewhat like a scythe or a question mark that has been laid over to the left and the sharp angle smoothed into a gentle curve. The flippers, located just aft of and below the posterior end of the jawline, are small and narrow.

Features that distinguish C. marginata from other right whales include a small and strongly hooked dorsal fin 25–30% of body length forward from the tip of the flukes, and two throat grooves.

The color is dark gray or black on the back, shading to paler on the belly. The inside of the mouth and tongue are ivory colored, as is the gum at the base of the baleen. The baleen is long and narrow, with very fine bristles, and it is creamy white in color except for the margin, which varies from brown to black. Each side of the jaw has 213 to 230 baleen plates, which measure up to 33 in (840–850 mm). The area of the filtering apparatus is relatively large for the body size.

The skeleton and skull are different from those of all other cetaceans. Caperea marginata has the most ribs (34–36) and the least number of vertebrae (40–44) of any cetacean. The ribs, wide and flat, become more so posteriorly, presumably to protect internal organs, and they extend farther aft than those of any other genera, leaving only two ribless vertebrae anterior to the tail. The seven cervical vertebrae are all fused.

C. marginata can easily be confused with the minke whale (Balaenoptera acutorostrata) when seen from the rear.

Distribution

The pygmy right whale appears to inhabit the Southern Hemisphere between latitudes 31° and 52°, in both coastal and pelagic waters of the Atlantic, Pacific, and Indian Oceans. More sightings—more than one-third of the total—have taken place off the coast of southeastern Australia, primarily off Tasmania, than anywhere else. Sightings and strandings have also occurred in South Africa, southern South America, New Zealand, The Falkland Islands, the Crozet Islands, and the south Atlantic Ocean.

Habitat

Caperea marginata inhabits temperate and sub-antarctic waters in coastal and pelagic zones, between the 5° and 20° isotherms.

Behavior

Little is known about this small, obscure species, because living animals have been observed only rarely. There have been fewer than 20 observations of individuals or groups at sea, partly due to the animal's inconspicuous behavior, and to the paucity of activity at the surface. Pods of up to ten animals have been seen, and in one instance, roughly 80 individuals were spotted together in pelagic waters, but most live pygmy right whales have been observed singly or in pairs.

Caperea marginata have been viewed in the company of dolphins and pilot (Globicephala melas), sei (B. borealis), and minke whales.

Caperea marginata usually swims slowly, around three to five knots, but can accelerate and swim very quickly if necessary, propagating a notable wake. It swims by flexing its body laterally, in waves. It does not appear to jump, and the blow is inconspicuous. Caperea marginata has been observed to dive for only up to four minutes at a time, surfacing briefly between dives.

Vocalizations are characterized as sounding like intense thumps or tone bursts, the volume of each quickly rising, then slowly falling, while the frequency drops. They come in cycles of 11–19, each with a mean duration of 180 m/sec, separated from each other by a mean of 460 m/sec.

Strandings can occur at any time of year, suggesting that pygmy right whales may not migrate seasonally. However, increased sightings and strandings in the waters off the Cape Peninsula of South Africa during December, January, and February have suggested a seasonal migration during these months.

Feeding ecology and diet

Diet appears to consist almost entirely of copepods, and possibly other plankton. Observations and comparisons with other copepod eaters (sei and right whales) suggest that C. marginata may use a surface-skimming technique for feeding.

As mentioned, increased sightings and strandings in the waters off the Cape Peninsula of South Africa from December to February have suggested a seasonal inward migration during these months, which coincides with an increase in the biomass of zooplankton that occurs during the Southern Hemisphere's spring and summer.

Reproductive biology

Little is known about reproductive biology. The mating season, the mating system, the gestation period, and the calving interval are all unknown. Some researchers believe that calving may take place yearround. Newborns are around 6.5 ft (2 m) and reach 9–11.5 ft (3.0–3.5 m) at weaning. Sexual maturity is reached at 16–20 ft (5–6 m).

Conservation status

Caperea marginata is now listed on appendix I of the CITES, meaning it is considered "Threatened, though it is not listed by the IUCN." Though it is the only baleen whale to escape large-scale commercial whaling, it is thought to be

comparatively rare. It may be at risk due to the difficulty of distinguishing it from the Antarctic minke whale (B. bonaerensis), 440 of which the Japanese harvested annually in the Southern Ocean. The International Whaling Commission has estimated population size due to lack of data. Caperea marginata is thought to be threatened by global climate change, but not by toxic contamination.

Significance to humans

Though C. marginata have never been caught commercially, individuals have been caught deliberately by inshore fisheries, and accidentally in fishing nets.

Resources

Books

Jefferson, T. A., S. Leatherwood, and M. A. Webber, eds.Marine Mammals of the World. Heidelberg: Springer-Verlag, 1993.

Kemper, Catherine M. "Pygmy Right Whale Caperea marginata." In Encyclopedia of Marine Mammals, edited by William F. Perrin, Bernd Würsig, and J. G. M. Thewissen. San Diego: Academic Press, 2000.

Periodicals

Árnason, Úlfur, Sólveig Grétarsdóttir, and Bengt Widegren. "Mysticete (Baleen Whale) Relationships Based upon the Sequence of the Common Cetacean DNA Satellite." Molecular Biology Evolution 9 (1992): 1018–1028.

Árnason, Úlfur, Anette Gullberg, and Bengt Widegren. "Cetacean Mitochondrial DNA Control Region: Sequences of All Extant Baleen Whales and Two Sperm Whale Species." Molecular Biology Evolution 10 (1993): 960–970.

Dawbin, William H., and Douglas H. Cato. "Sounds of a Pygmy Right Whale (Caperea marginata)." Marine Mammal Science 8, no. 3 (July 1992): 213–219.

Kemper, Catherine M. "Sightings and Strandings of the Pygmy Right Whale Caperea marginata Near Port Lincoln, South Australia and a Review of other Australasian Sightings." Transactions of the Royal Society of South Australia 121 (1997): 79–82.

——. "Distribution of the Pygmy Right Whale, Caperea marginata, in the Australasian Region." Marine Mammal Science 18, no. 1 (2002): 99–111.

——. "New Information on the Feeding Habits and Baleen Morphology of the Pygmy Right Whale Caperea marginata." Marine Mammal Science 8, no. 3 (July 1992): 288–293.