The Curious Tale of a Far-Flung Whale

When marine biologists first spotted the humpback whale AHWC no. 1363, there did not appear to be anything remarkable about her at all. Seen with another female on the Abrolhos Bank off the coast of Brazil on August 7th, 1999, the whale simply stuck around long enough for the scientists to snap a few photographs and collect genetic data before everyone went off on their own way.

1363 would not be seen again for two years. When she did turn up, it was in a place marine biologists were not expecting. On September 21, 2001 the whale was photographed again by members of a commercial whale-watching tour in a humpback whale breeding ground off the east coast of Madagascar, nearly 10,000 kilometers to the east. This is the longest distance any humpback whale – or any mammal without an airline ticket, for that matter – has migrated, with the previous record being set by a group of seven humpbacks which swam approximately 8,300 kilometers from Antarctica to the west coast of Costa Rica. According to Peter Stevick, a College of the Atlantic marine biologist and lead author of the paper describing 1363’s journey, “This observation is altogether unprecedented. There are only a few humpback whales that have been seen in more than one breeding ground before this, and they moved to relatively nearby areas – eastern to western Australia, eastern to western Africa for example.”

Humpback whales are well-known long-distance travelers. Almost every year humpback whales in populations all over the world migrate from the cool, productive waters closer to the poles towards the tropics, where the whales breed and pregnant females give birth. Calves typically learn which route to take from their mothers during their trip from the breeding groups back to the cooler feeding grounds.

In the case of the whales which winter off Brazil, Stevick says, most of them start their journey around the South Sandwich Islands and South Georgia off the southern tip of South America and follow a relatively direct route. Whales elsewhere typically follow straightforward paths, too. It is one of the classic migrations – a staple of cable documentaries – but 1363 bucked the trend. Whereas most whales travel up and down the latitudes within particular corridors, 1363 went in an entirely different direction and crossed several migratory corridors. A whale going from one feeding corridor to an adjacent breeding corridor is not unheard of, but scientists had never before seen a whale which veered east and swam such a considerable distance.

Why 1363 traveled so far is unknown. For male humpbacks, traveling between corridors would have the advantage of providing mating opportunities and so it would be expected that they would range further afield. But 1363 was a female. Would a female humpback also gain some sort of mating benefit by moving into a new area, or is there something else going on? Did she misread a migratory cue and got lost before taking up residence somewhere else? And why did she move east when most whales which migrate between corridors head west towards South America? One possibility is that 1363 started off in one direction and simply found it easier to go to a different breeding site. “An unusually long feeding trip, particularly likely in an atypical prey year,” Stevick says, “could take her to a point where, when migration time arrived, it was shorter and easier for her to go to a different breeding site than expend the extra effort to return ‘home’.”

Since we don’t know what she was doing between 1999 and 2001, there is no way to tell for sure. What 1363’s remarkable migration does show, however, is that humpback whales are more flexible in their behavior and choices of breeding populations than was previously understood. Many still swim up and down the latitudes along their corridors according to time of year and stage of the reproductive cycle, but there may be a degree of mixing between populations which scientists are only just beginning to identify. As Stevick points out, “…while the journey of this one whale is extreme, her example shows us that we should pay attention; whales may not always do what we expect or remain in tidy groups.”

References:

Stevick, P., Neves, M., Johansen, F., Engel, M., Allen, J., Marcondes, M., & Carlson, C. (2010). A quarter of a world away: female humpback whale moves 10 000 km between breeding areas Biology Letters DOI: 10.1098/rsbl.2010.0717

Rizzo, L., & Schulte, D. (2009). A review of humpback whales’ migration patterns worldwide and their consequences to gene flow Journal of the Marine Biological Association of the United Kingdom, 89 (05) DOI: 10.1017/S0025315409000332