It is one of the most remarkable journeys by any creature on the planet – and it is made by one of the biggest creatures known to science.
Researchers have shown that humpback whales travelling between breeding grounds off the west coast of Central America and feeding grounds off Antarctica clocked up more than 5,000 miles on one leg of their journey – the largest recorded journey by any individual mammal.
The researchers believe the whales are heading for warmer waters in which to give birth to their calves. Mark Simmonds, director of science at the Whale and Dolphin Conservation Society, who was not involved in the research, said: “It has this extraordinary lifestyle with its breeding grounds in one place and its feeding grounds far away.”
Kristin Rasmussen at the Cascadia Research Collective in Olympia, Washington, and her colleagues made daily excursions in small boats off the coaf Central America to observe the whales between June and October. They took photographs of the underside of the animals’ tails so that they could be identified at the other end of their journey.
“Just like humans have unique fingerprints, whales have unique tail markings,” said Ms Rasmussen.
During the Antarctic summer, the team made similar observations and looked for whales which had been spotted in the tropical waters. Seven animals were photographed in both locations and a mother and calf pair were seen in Antarctic waters 161 days after they had been spotted off Costa Rica, having travelled 5,266 miles. Another individual was seen in different years at locations 5,288 miles apart. The study is reported in the journal Biology Letters.
The study ends the controversy over which whale species travels the furthest, according to Mr Simmonds. The grey whale’s migration from Mexico to the Arctic is also an impressive voyage. Blue whales – the largest animals on the planet – also migrate thousands of miles, with the North Atlantic population moving from Arctic feeding grounds to waters off the eastern seaboard of the US. But none of these animals have been shown to travel as far as the humpbacks.
The humpback whales studied by Ms Rasmussen cross the equator on their journey up from the Antarctic to reach their preferred breeding grounds. To work out why they go so far, the team looked at satellite measures of sea surface temperatures for the wintering grounds of 24 humpback whale populations around the world.
In all cases, the animals were opting for waters around 24-25C. The whales she studied off the coast of South America would have to continue beyond the equator to find water this warm. Ms Rasmussen believes that a high enough water temperature is crucial for them to breed. “It’s likely that being in warm water is somehow beneficial to the calf.”
Humpbacks are also famous for their song, a favourite with therapists and masseurs the world over, produced by males during the winter to attract mates. “They all pretty much sing the same song at the breeding ground and that undulating noise develops through the breeding season,” said Mr Simmonds. They stop singing when they leave the breeding grounds, but continue with their evolving tune when they return. “They resume the song at the same point that they left off.”
Japan has announced plans to add 50 humpback whales to its “scientific” catch quota. Mr Simmonds believes that is a political gesture to provoke anti-whaling nations such as Australia and Britain: “They are fully aware that the humpback whale is hugely popular.”
Source: Guardian (UK)