The pygmy right whale Caperea marginata (Gray, 1846) is the smallest baleen whale and the only member of the family Neobalaenidae (Fig. 1). Its diagnostic features include long, narrow, creamy-white baleen with an outer margin of brown or black and very fine bristles; a clearly visible band of white gum at the base of the baleen; a moderately arched rostrum that becomes more pronounced as the animal grows; a small, falcate dorsal fin placed about 25 to 30% of body length from the tail; and shallow throat creases in some animals. The overall body shape of adults is stouter than rorquals but not as broad as right and bowhead whales.The flukes are very broad and have a deep medial notch. The body is pale to dark gray above and pale gray to white below. There is a dark eyepatch and an indistinct pale gray chevron across the back behind the blowhole. The oval scars of cookie-cutter sharks Isistius spp. are often present. The flippers are small, narrow, and rounded at the tip and are dark gray above (contrasting sharply with the pale color of the sides of the body) and paler below. Mandibular and rostral hairs persist into adulthood but there are no callosities as in true right whales.
Figure 1 Baleen tvhales include some of the la rger whale species. The smallest baleen whale is the pygmy right whale (Caperea marginata) which achieves a maximum length not exceeding 6.5 m. Skeletal differences are especially distinctive and warrant the recognition of this species as the sole member of the Neobalaenidae, separate from other baleen whales.
At sea, pygmy right whales may be confused with minke whales Balaenoptera acutorostrata and B. bonacrensis, but close inspection should reveal some of the diagnostic features noted earlier. The blunter rostrum of the pygmv right whale and its habit of swimming with its head “thrown” out of the water at an angle should also help identify it.
The skull and skeleton of the pygmy right whale are unlike any other cetacean. The supraoccipital bone is very long, extending well forward on the skull. The ear bone has a distinctive wrinkle on its outer surface and is squarish in outline.
The mandibles and ribs are very broad and flat. The numerous ribs (18 pairs) extend well along the body. All seven cervical vertebrae are fused and the total number of vertebrae is only 44. The flipper has only four digits.
I. Recent and Fossil Relationships
Although the pygmy right whale has sometimes been included in the family Balaenidae, recent studies of its morphology and genetic makeup have shown that its present position in Neobalaenidae is correct. It is believed to be more closely related to the gray whale (Eschrichtiidae) and rorquals (Balaenopteridae) than to right and bowhead whales (Balaenidae). Geographical variation has not been studied and no subspecies are recognized. No fossil neobalaenids have been described. A reported fossil, Bal-aena simpsoni, from Chile is believed to be related to Balaenidae.
II. Distribution and Habitat
This species is found only in the Southern Hemisphere (Fig. 2). It is circumpolar, between about 30° and 55°S, with records from southern Africa, South America, and Australia and throughout New Zealand. It has also been recorded in the vicinity of the Falkland and Crozet islands and in the open ocean of the South Atlantic and south of Australia.
The pygmy right whale lives in temperate and subantarctic regions where water temperatures are between about 5° and 20°C. It has been seen in oceanic and neritic environments where some individuals have spent up to 2 months very close to shore, possibly feeding while there. Seasonal movements inshore may be related to die availability of food there during spring and summer. Although oceanic feeding has not been observed, animals collected there had full stomachs. The little information available on diet suggests that copepods, euphausi-ids, and possibly other small plankton are eaten. The predators of pygmy right whales are not known.
Figure 2 Distribution of the pygmy right whale. Dots show position only, not number, of records.
Its behavior is inconspicuous, but because so few observations have been reported, the complete repertoire may not have been recorded. Swimming speeds of 3 to 5 knots have been noted, but it is also capable of very fast acceleration and speed, leaving a conspicuous wake when doing so. One underwater observation of swimming noted that the body action was very flexed. When pygmy right whales dive they remain submerged for up to 4 min and surface briefly before diving again. The blow is inconspicuous and, when visible, is small and oval. The sounds of one solitary juvenile consisted of short, thump-like pulses or tone bursts with a downsweep in frequency and decaying in amplitude. Most energy was between 60 and 120 Hz.
Less than 20 sightings of pygmy right whales “at sea” have been recorded. They have been seen with pilot (Globicephala melas), sei (Balaenoptera borealis), and minke whales and with dolphins. Mostly these have been of 1 or 2 animals, but groups of up to 10 animals are known and one group of about 80 pygmy right whales was seen in oceanic waters. Strandings throughout the year in Australia and New Zealand suggest that the species does not migrate north-south as do most other baleen whales.
IV. Life History
Relatively little is known of the life history of pygmy right whales. Length at birth is about 2 m and at weaning is about 3.0-3.5 m. Most animals are physically mature at around 6 in, and maximum length and weight are 6.5 m and 3430 kg. Females are slightly longer than males. Sexual maturity may occur at lengths of greater than 5 m. The calving interval, mating season, and gestation period are all not known. The calving season is protracted, possibly year-round. Life expectancy is not known and no age estimates have been made.
V. Interactions with Humans
Pygmy right whales were never targeted by whalers, although they were taken opportunistically. Intentional killing by inshore fisheries and incidental captures in fishing nets are known. No animal has been kept in captivity. Toxic contaminants are not believed to be a threat to this species because tissue levels of organochlorines and heavy metals measured in a few animals have been low.