Crowdsourced photographs reveal that some humpback whales travel between Mexico and Hawaii in one breeding season
Humpback whales may be far more mobile during their breeding season than previously thought, with some travelling up to 6000 kilometres in search of a mate.
Humpback whales (Megaptera novaeangliae) are found in all major oceans. Those in the North Pacific typically spend their summers feeding around Alaska and Canada before migrating south in the winter to waters near Mexico and Hawaii for breeding.
Historically, scientists have assumed that the whales choose either Mexico or Hawaii as a breeding site. However, some evidence, such as shared whale songs, suggests that the two groups may mix.
To investigate further, James Darling at Whale Trust Maui in Hawaii and his colleagues studied a database of photos of more than 26,000 individual humpback whales in the North Pacific taken by professional and amateur photographers since 1977.
Whales have distinct skin pigment markings on the underside of their tails that allow them to be accurately identified. Using software, the researchers recognised two whales that were photographed in both Hawaii and Mexico during the same winter breeding seasons.
One male had travelled 4545 kilometres in 53 days, leaving a group off Olowalu on the Hawaiian island of Maui to join a group of three whales off Isla Clarión in the Revillagigedo archipelago of Mexico in 2006.
A second whale – probably also a male – had travelled 5944 kilometres from south of Zihuatanejo in Mexico to waters in the ʻAuʻau Channel off Maui 49 days later, in winter 2018. There, it was one of seven whales pursuing a single female, as a challenger to her primary mate.
“Our first reaction was, ‘You’ve got to be kidding me!’” says Darling. But distances that seem enormous to humans may not be significant to whales. “They might just be travelling the ocean like it’s their own backyard,” he says. “This really changes the way we think about whales.”
In summer months, observers had spotted both these animals in northern feeding grounds off the Canadian and Alaskan coasts.
While the matched photos in the study happened to show males, females may also be making these long treks, says Darling. “If the males were out there following females, it would make more sense than them out there by themselves swimming for 40 days sans females during the breeding season,” he says.
Whales usually travel at coasting speeds of around 4 kilometres per hour, says Darling. Even if these whales had been photographed exactly on their departure and arrival dates, calculations suggest they were swimming faster than this.
The findings indicate that there aren’t distinct populations of whales in the north-east Pacific, but rather several overlapping groups, says Darling. The results also call into question rules concerning the whales’ conservation status, he says. Since the 1990s, for example, whales overwintering in Mexico are considered endangered, whereas those overwintering around Hawaii are labelled “not at risk”.
Journal reference: Biology Letters, DOI: 10.1098/rsbl.2021.0547
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