Whale of the Month - Gray Whale

Species fact file

Common names: gray whale, grey whale, gray back whale

Icelandic name: sandlægja

Scientific name: Eschrichtius robustus

Family: Eschrichtiidae (gray whales), although recent studies suggest placement in Balaenopteridae (rorqual whales) instead

Max length: 14m (males), 14.9m (females)

Distribution: North Pacific Ocean and Pacific-adjacent areas of the Arctic

Once abundant in the North Atlantic, gray whales were driven extinct in European waters as early as AD 500 – possibly due to whaling. They persisted off the Atlantic coast of America and around Greenland, and there are records of gray whales in Iceland throughout the 1600s, but by the early 1700s they had been wiped out. However, there have been a few sporadic sightings of gray whales outside of the Pacific in the past decade: in the Mediterranean, and even in the South Atlantic.  

Aside from these few Atlantic wanderers, gray whales are now only found in the Pacific Ocean. They are divided into the Eastern North Pacific (ENP) and Western North Pacific (WNP) populations. The WNP population is found mostly in waters between Japan and Russia, but it is poorly known and very small – probably numbering between 200-300 individuals.

The ENP population was exploited heavily by whalers in the 19th century, but has since recovered and was recently estimated at over 24,000 whales. This population migrates up and down the west coast of America between their feeding grounds in Siberia and Alaska and their breeding grounds in the lagoons of Mexico. This annual round trip of 16,000 - 25,000km is the longest of any mammal.

Some gray whales migrate all the way from the WNP feeding grounds in Sakhalin Island, just north of Japan, to the breeding lagoons in Mexico with the ENP whales. This suggests that some of the gray whales which feed in the Western Pacific don’t actually belong to the WNP population at all, and that there is some mixing between the two populations in these feeding grounds.

This map shows the range of the ENP and WNP populations of gray whales, with the red line indicating the migration that some individuals make from one side of the Pacific to the other! Image from the International Whaling Commission.

Gray whales are unusual record-holders in the whale world: they are host to the greatest variety of ‘ectoparasites’, small animals which live on their skin. The most well-known of these freeloaders are barnacles, which gray whales pick up in their warm winter breeding grounds. The barnacles usually live for about a year and drop off in the colder waters where the whales feed in summer, leaving behind patches of de-pigmented scar tissue which gives gray whales their mottled colouring. The patterns created by these white patches can be used by biologists for photo identification. One species of barnacle, Cryptolepas rhachianecti, has such a close relationship with these whales that it is described as ‘host-specific’ – gray whales are the only place this barnacle will grow!

Barnacles are not the only parasites gray whales carry – they are also host to whale lice. Whale lice typically live in the areas around the barnacles, giving these patches an orange colour. Neither the whale lice nor the barnacles do much harm to gray whales. Barnacles are filter-feeders, collecting debris and small animals from the water, and just use the whales for a free ride. Whale lice feed on algae that grows on the whale’s skin, as well as dead and damaged skin.

A patch of barnacles and whale lice on a gray whale’s head. Photo by Joe McKenna.

Although this sounds unpleasant, it can actually be good for the whale. One female gray whale was struck by a Russian whaling harpoon in the 1980s. Incredibly, she survived, and is still spotted migrating up and down the coast of America every year. But this serious injury left her with a large scar on her back and has earned her the nickname ‘Scarback’. Over 30 years later, the wound is still not fully healed, and the scar is teeming with whale lice. These lice feed on the dead and decaying tissue, keeping the wound clean – if not for the whale lice, Scarback may not have survived this long with such an injury.

Gray whales are also unique in the way that they feed. Like other baleen whales, they feed on small aquatic invertebrates; but unlike other baleen whales, they like to hunt for these animals in the seabed itself rather than in the water. Their baleen plates are very short and coarse, which allows the gray whales to filter out particles of sand and mud in the way that other baleen whales filter out water. This is a pretty handy adaptation to have when your dinner is literally a mouthful of sand!

Learn more about...

Gray whales migrating from Sakhalin Island, Russia, to breeding lagoons in Mexico

How fossilised whale barnacles can reveal ancient migration routes