Crowdsourced photographs reveal that some humpback whales travel between Mexico and Hawaii in one breeding season
16 February 2022
Humpback whales may be far more mobile during their breeding season than previously thought, with some travelling up to 6000 kilometres in search of mates.
Humpback whales (Megaptera novaeangliae) are found in all major oceans. Those in the North Pacific typically spend their summers feeding around Alaska and Canada and migrate south near Mexico and Hawaii in the winter for breeding.
Historically, scientists have assumed that the whales choose either Mexico or Hawaii as a breeding site. However, in 2018, researchers identified shared whale songs in what they assumed were two separate winter whale populations in Hawaii and Mexico.
To investigate further, James Darling at Whale Trust Maui in Hawaii and his colleagues gathered photos of more than 26,000 individual humpback whales 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 winter breeding seasons.
One male had travelled 4545 kilometres in 53 days, leaving a group off Olowalu, Hawaii, 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 West Maui 49 days later, in winter 2018. There, it was one of seven whales pursuing a single female, as a secondary escort or a challenger to the female’s primary mate.
“Our first reaction was ‘you’ve got to be kidding me!’” Darling says. But distances that seem enormous to humans may not be significant to whales. “They might just be traveling the ocean like it’s their own backyard. This really changes the way we think about whales.”
In summer months, observers had spotted both these males in northern feeding grounds off the Canadian and Alaskan coasts.
While the results of the study – based entirely on serendipitous snapshots – only show males, females may also be making these long treks, Darling adds. “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 breeding season,” he says.
Whales usually travel at coasting speeds of around 4 kilometres per hour, Darling says. Even if these whales had been photographed exactly on the departure and arrival dates, calculations would suggest they were traveling faster than this.
The findings suggest that there are not distinct populations of whales in the Northeast Pacific, but rather several overlapping populations, Darling says. 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: https://doi.org/10.1098/rsbl.2021.0547
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