Paul Falkowski

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 between 24 and 25oC. The whales in this study would have had to continue north of the Equator to find water this warm. 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”, she says. The researchers sighted a total of 207 whales off Central America in 2001–2004 winter surveys. Mother–calf pairs, groups of competing males and singing males were all recorded. Fortyone whales were individually identified photographically: of these, seven were also photographed off the Antarctic peninsula. Three of these whales were seen within the same year: one off Costa Rica 262 days after it was seen in Antarctica and two — a mother and calf pair — off Antarctica 161 days after being seen off Costa Rica. The researchers calculated that the distances between these two sites ranged from 8300 kilometres to 8460 kilometres. The researchers also found that the wintering areas off Central America were the chosen favourite locations for northern humpback whales migrating from the Arctic. “Eastern North and South pacific populations share genetic traits indicating a transequatorial exchange, probably off Central America,” the authors write. “Our analysis shows that worldwide humpback whale wintering areas are found in warm coastal waters irrespective of latitude,” the authors write. “In the ongoing debate on the reasons for migration, this result supports previous ideas linking temperature at the wintering area to energetic strategies.” The authors suggest that, as in terrestrial mammals, energy conserved during offspring development can be devoted to growth, leading to larger size and increased reproductive success in adulthood. Q & A