Beaked whales

little known, and fascinating

I had never even heard of the beaked whales until a couple of years ago, when a news article reported a dead one, of a rare species, stranded on a beach somewhere in the southern hemisphere. Then I recently saw the partial skeleton of one in the Park Service section of the Glacier Bay lodge; this whale had washed up on the beach south of Yakutat and the remains were salvaged. It was clear, from some superficial reading, that beaked whales have not been studied much; some seem to be rare and one species has been seen alive in the wild only once, some perhaps never. Most of the available information comes from stranded or hunter-killed individuals. The more I thought about it, the more it sounded like fun to do a little bit of digging for some information about these poorly understood and therefore somewhat mysterious whales.

There are perhaps twenty-one species of beaked whales in the world. They have pointed snouts (‘beaks’) that are clearly defined in some species but less so in others. On the lower jaw, all species have one or two pairs of teeth that protrude when the mouth is closed; in almost all species, only the adult males have teeth that erupt from the gums, although females and juveniles may have un-erupted teeth. In some, the teeth are at the tip of the jaw, while in others, especially those with large, tusk-like teeth, the teeth are partway back from the tip. These tusks seem to be used for fighting, and adult males are often much scratched and scarred.

beaked-whale-skull
Skull of a beaked whale. Photo by Katherine Hocker

Beaked whales are deep-sea foragers, making very long, deep dives to the sea bed. They seem to be most common around under-sea canyons, sea-mounts, and the slope of the continental shelf. They are suction feeders, hosing up mostly squid, but also fish and sometimes octopuses, crustaceans, sea cucumbers, and tunicates. Their short pectoral fins can be folded back into shallow pockets along the side. Very little is known about their reproductive habits. They are reported to be very sensitive to high intensity sonar, not so much from direct physical damage as indirectly, from disruption of their normal diving behavior, causing them to dive or surface too rapidly, before the body is prepared for the change.

There are three species in the North Pacific/Gulf of Alaska waters (two of these have been subject to commercial whaling, near Japan). I will give the scientific names here, to make it clear that the three species are in three different genera, and are therefore considered to be quite distinct.

The specimen on display in Glacier Bay is Baird’s beaked whale (Berardius bairdii), the biggest of all the beaked whales, averaging about thirty-eight feet in length (longer than an average orca). The sign on the display says, wonderingly, that they have the densest bones of any mammal and thirteen stomachs (I have not found reference to these observations elsewhere). Unlike all the other genera of beaked whales, both male and female have erupted teeth, two exposed on the tip of the lower jaw and two smaller ones partway back, concealed within the closed mouth. They appear to forage commonly at depths of eight hundred to four thousand feet, sometimes staying down for over an hour, but they are capable of diving down well over a mile. Very deep dives are usually interspersed with a series of shallower ones. They commonly travel in social groups of up to twenty individuals, but sometimes as many as fifty. Females are said mature at age ten to fifteen years, but males at six to eleven years. After a long gestation period, variously stated as twelve to seventeen months, females give birth, at intervals of about three years. They may live over fifty years (females) or over eighty years (males).

Stejneger’s beaked whale (Mesoplodon stejnegeri), also known as the saber-toothed whale and the Bering Sea beaked whale, averages about sixteen feet in length. They are reported to be found mostly in deep water, half a mile or a mile deep. They travel in small groups of two to five individuals, but sometimes ten or more. Adult males have triangular tusks midway on the lower jaw; the tusks stick up beyond the upper jaw when the mouth is closed. Some specimens have healed jaw fractures, suggestive of intensive fighting. Parallel scars in a related, tusked species suggest that fighting may include striking each other with the snout so the tusks cut the opponent. Milk from a stranded, lactating female had less fat and much more protein than the milk of belugas or sperm whales, and was a surprising blue-green in color.

Cuvier’s beaked whale (Ziphius cavirostris), sometimes called the goose-beaked whale, is found around the world except in the Arctic. They average about twenty feet in length. Males have two teeth at the tip of the lower jaw. They tend to travel in small groups, but sometimes up to twenty-five individuals, mostly females. They favor slope waters where the depth changes markedly over a short distance. They can dive to depths well over a mile and stay down for two hours. Deep dives are often interspersed with time near the surface and shallow dives. Studies of this whale near Hawaii suggest that adult females may show considerable site fidelity, reappearing in the same location in different years. Gestation has been estimated to last about a year, with a two-to-three year birth interval.

I love the fact that here is a whole group of mammals about which so little is known. Published accounts do not always agree about various supposed ‘facts’, reflecting the sparsity of good data. In a way this is humbling, because it clearly shows that we are very far from knowing it all. And it is exciting, because it means that there is still a lot to learn! What fun.

%d bloggers like this: