Delphinids: Right Whale Dolphins

Northern right whale dolphin

Dolphins are familiar animals. We see them at aquaria and boat trips to see them in the wild are relatively common. In recent decades, there has been a rise in 'swimming with dolphins' tourist experiences, which studies have shown to be good in the short term for humans, but less so in the long term for the dolphins. Either way, we know a fair amount about them, both culturally and scientifically and, depending on the part of the world you live in, there may be many different species that you can see.

Some dolphin species, however, are less well-known than others. I've come some already, but perhaps the most obscure are the right whale dolphins. 

This is not because they're particularly rare. In fact, their population is thought to be quite high. Instead, a couple of factors are likely to be responsible. For one, they like deep water, and while they will approach close to the coast if the seabed drops off sharply enough, they are much more likely to be seen far from land. For another, they don't often bow-ride. Most other dolphins do, deliberately swimming into the bow wave of a ship, perhaps out of curiosity about the strange object moving across the surface, or perhaps for the fun of splashing in the choppy waves. But, either way, right whale dolphins rarely do, preferring to keep their distance from humans and their craft.

The better-known of the two species is the northern right whale dolphin (Lissodelphis borealis) first named by American naturalist Titian Peale in 1848. He initially described it as a species of beluga whale and subsequent authors shuffled it around among other genera before eventually agreeing that it very obviously belonged in Lissodelphis, a genus originally named for the southern species and so distinctive that it has sometimes been argued that it ought to be considered a subfamily. 

The name Lissodelphis translates as "smooth dolphin", and, looking at the animal, one can see why that was chosen. Right whale dolphins are slender and elongated, typically around 3 metres (9' 10") in length but weighing only around 115 kg (255 lbs), with a short beak and relatively small flippers and flukes. Most significantly, however, their smooth-bodied look comes from the fact that, unlike all other species of dolphin, but like right whales, they have no dorsal fin. The resulting body form has often been described as "torpedo-shaped".

The northern right whale dolphin is mostly black, but has a large white patch on the chest that extends back to form a narrow streak that runs all the way to the tail. While there is some variation in the detailed pattern, there is also a white spot on the underside of the chin and white undersides to the flukes. 

The species is found in the North Pacific, roughly between 30° and 50° north. On the American side, that's essentially the entire west coast of the contiguous US, and on the other, it runs roughly from the southern tip of Kamchatka to central Japan. Their ideal water temperature is thought to be around 9° C (48° F), but there's a fair degree of tolerance either way, and northern right whale dolphins have occasionally been seen as far north as the Gulf of Alaska and as far south as Baja California. 

Even so, they are seen so rarely that it was possible to write in 1976 - over a hundred years since Peale had collected his first specimen off the coast of the Oregon Territory - that there had only ever been 32 published sightings in the eastern Pacific. Ten of those were strandings, although, obviously, we're excluding what must have been several random sightings by sailors that were never written up, not to mention anything on the Asian side. In any event, since that time, a great many have been recorded as being killed by driftnet fishing, although not sufficient to endanger the species (so far).

Their preferred food are lanternfish, reported as comprising as much as 89% of their diet in the central north Pacific. Further south, market squid are the second-most common food eaten, but they also eat other squid, and some fish, most notably hake. 

Right whale dolphins are sociable animals, with pods containing one or two hundred individuals. At times, multiple pods temporarily merge into even larger aggregations, which can contain well over a thousand dolphins. With sleek bodies and lack of a dorsal fin, when they are swimming normally at the surface, they can be hard to notice unless the sea is especially calm. They can also move fast, with speeds of 40 km/h (25 mph) having been recorded. Nonetheless, they do sometimes make shallow leaps or slap the water with their tails, as other dolphins do and, even if bow-riding is rare, that isn't to say it never happens.

A 2007 study reports that they have never been known to whistle, something common to other dolphin species. Instead, they appear to communicate using rapid bursts of clicks, similar, but deeper in tone than those they use to echolocate. These, however, are likely to be able to convey less nuanced information than whistles, although it's always possible that there's detail we've missed.

Very young dolphins are most commonly seen in mid-summer. Assuming a 12-month gestation period, which seems likely, that would also be the breeding season, with each female giving birth about once every other year. But with so few sightings, even that is uncertain, and further details of their reproductive and social lives remain a mystery.

Southern right whale dolphins

We know even less about the southern right whale dolphin (Lissodelphis peronii). Surprisingly, however, these were the first to be described, all the way back in 1804. The initial description came from François Péron, who had seen one off the south coast of Tasmania while serving as official (or, more accurately, "sole surviving") zoologist to the Baudin Expedition to Australia on behalf of Napoleon. Technically, he gave the animal its first scientific name, but the manuscript was never published, so it's Lacèpéde's name that stuck... which, since it honours Péron, is arguably better. Indeed, the animal is still sometimes called "Péron's dolphin", especially in French.

The two species look extremely similar, to the extent that some scientists have argued that they should really be considered the same species. About the only difference is that the southern species has far more white on its body, with the narrow streak along the abdomen being replaced by a much wider splash that wraps up around the flanks. The face is also white, as are the flippers, although they often have a black stripe along the trailing edge.

One reason that it would be surprising for the two to be the same species is that they live at opposite ends of the globe, and so must have remained separated for a long time. The southern right whale dolphin lives between 30° and 65° south, where the geography of the Southern Hemisphere allows it to spread in a full circle around the world. It lives off the southern coasts of Australia and Africa, and around many of the remote southern islands, most notably the Falklands. Its preference for waters between 1 and 20° C (34 to 68° F) means, however, that it can follow the cold Humboldt Current much further up the west coast of South America, allowing it to reach as far as Peru.

Like its northern relative, however, it prefers deep water, with an absolute minimum of around 200 metres (660 feet) and preferably much more, since they prefer to dive at least that deep in search of food. This means that it rarely approaches the coast unless there is a suitable underwater canyon in the area. Its southernmost extent is marked by the Antarctic Convergence, the current isolating Antarctica beyond which sea temperatures rapidly become too cold for it to tolerate.

From studies of their stomach contents, we can tell that they feed mostly over the outer stretches of the continental shelves, and that their prey consists of a mixture of squid and fish, with lanternfish probably predominating. They live in groups at least as large as their northern kin, and possibly larger, with few pods definitively recorded as having fewer than 200 members. 

And that's pretty much everything we know. Details of their breeding, for example, remain almost entirely unknown, although they have been reported to successfully hybridise with dusky dolphins. On the basis of this, and other genetic data, while the idea of giving right whale dolphins a subfamily all to themselves is no longer followed, they do have a subfamily named after them, which also includes dusky dolphins and some of the smaller southern species.

With that, I have finished all of the delphinid species that are commonly described as "dolphins". There are, however, four other species that, from a scientific point of view, are undeniably dolphins but that we don't normally think of as such. Next time, I will look at two of them.

[Photos from the NOAA Photo Library. In the public domain.]