In this blog, examine for yourself the development of one individual's callosity in the series of images posted here; first, in the waters off the coast of Georgia, as a calf of a little more than one month in age (above); second, about 6 months later in the Bay of Fundy (below); and third, at 11 months of age with a distinctive callosity, seen back here in the calving grounds still with its mother (bottom).
Callosities are large patches of raised epithelial tissue, gray or black in color. They are composed of cornified skin, like a callus, and they form in many of the same places as hair does on men (i.e, along the jaw and above the eyes and lips). This tissue eventually becomes infested with thousands of light-colored cyamids (whale lice) which contrasts against the surrounding areas of black skin, thereby defining the callosity outline. (Check out this other blog to see an incredible close-up photo of whale lice, albeit a different species which colonizes the Southern Right Whales rather than the North Atlantic right whale.)
When a calf is born, a different species of cyamid, orange in color, is thought to be transferred to the calf from the mom's genitalia and mammary slits. These orange cyamids (shown in the above image of the 7-month-old) have no free-swimming stage but do move around on the calf, often concentrating on the lip ridges and other areas of the head; however, the location of these cyamids bears no correspondence to the whale's adult callosity topography. As the calf matures, the light-colored cyamids transfer from the mother and begin colonizing the calf in the areas of the cornified skin, developing into a callosity pattern which can be used to identify individuals. For instance, in the adjacent picture, the 11-month-old (shown on left) would be described as having a 'broken callosity, with long peninsular coaming (LPC), no lip callosities, and 2 post-blowhole-callosites'. (See more about Right Whale Head Codes here.). Interestingly enough, the mother (seen on the right) also has a very similar callosity pattern, except that she has a single post-blowhole callosity. This lends even more credence to Philip's speculation that whales may inherit callosity patterns from their parents. Learn about right whale photo-id in depth here and practice your own matching skills with the Aquarium's interactive Right Whale Matching Game. You may also like the Aquarium's callosity page for a great look at cyamids.
Photo Credit for top image: Stephanie Grassia, Wildlife Trust. Taken under a Scientific Research Permit issued by the National Marine Fisheries Service/NOAA.
Photo Credit for middle image: Marilyn Marx, New England Aquarium
Photo Credit for bottom image: Suzie Hanlan, New England Aquarium