Half of 21 tagged southern right whales took a 64-day detour and still arrived with the rest

Twenty-one southern right whales fitted with satellite tags left New Zealand’s subantarctic Auckland Islands and split into two camps on the way to their feeding grounds south of Australia. About half swam straight west, and the rest dropped far to the south before turning north in a big L-shaped loop. The surprise is the arrival schedule: both groups showed up at about the same time.

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The detour was not wasted time so much as a head start. Whales on the long route set off roughly a month before their shortcut-taking counterparts and traveled more slowly, which let two very different journeys converge on the same dinner table, an outcome that would be hard to predict from the routes alone. The pattern suggests migration in these animals is a flexible plan rather than a fixed road, and it carries a hopeful message about how a recovering population may cope with changing seas.

Two routes, 64 days against 42

The work was reported in Proceedings of the Royal Society B on October 14 by a team from the University of Auckland, and described in a news release distributed through EurekAlert. The study followed 21 whales, known in te reo Maori as tohora, from the Auckland Islands, also called Maungahuka, to waters south of Australia. The mean trip lasted 64 days on the long L-shaped route and 42 days on the direct westward one, a gap of 22 days.

Leena Riekkola, the lead author, and Emma Carroll, an associate professor at the University of Auckland, are the two authors named in the release. Riekkola likened the whales to travelers on a road trip who weigh different priorities along the way. The release lists several funders, including Royal Society Te Aparangi, the Live Ocean Foundation, the International Whaling Commission’s Southern Ocean Research Partnership and the Antarctic and Southern Ocean Coalition, and it states no conflicts of interest. The full paper is titled “Multiple strategies and cues define baleen whale migration,” with a digital object identifier that resolves to the journal.

What steers a whale across open ocean

With no landmarks in open water, the whales appear to read the ocean itself. The release says their movements lined up with major ocean currents, underwater features and subtle variations in Earth’s magnetic field. Those cues help explain how animals that leave on different dates and take different paths still reach the same place within about the same window, since each can adjust to what the sea offers along the way.

Individual circumstances also seem to shape the choice. According to the release, a female might delay migration so that her calf can grow, then take the shorter route; in a year when she travels alone, she may choose the longer one. Carroll drew the conservation lesson in plain terms: “A population that can adapt its behaviour has a better chance of coping with changing seas.”

Tagging from the Auckland Islands since 2020

The new paper sits on a long run of tagging work. In 2020, a University of Auckland announcement described a team led by Carroll attaching satellite tags to six whales at Port Ross on Auckland Island, more than 400 kilometers south of Stewart Island. The animals headed south toward Antarctica rather than north to warmer water, as the scientists had expected, and stayed in the islands region longer than predicted, which hinted that the area matters to them.

Later tags revealed far longer journeys. New Zealand Geographic reported that a whale nicknamed Bill, tagged in 2020, left the Auckland Islands in August of that year, traveled into the Indian Ocean, visited the Antarctic ice edge and came back in June, covering well over 15,000 kilometers. Carroll told the magazine the pattern suggests the population has resilience, since whales can still find food if one area becomes less productive. The magazine added that Carroll’s team deployed 11 more satellite tags at the Auckland Islands, planning to compare the tracks with currents, ocean productivity and marine heatwaves, the same kinds of environmental cues the new study examines.

The charity-backed Voyages of the Tohora project reports that most tagged whales travel west under Australia rather than east of New Zealand, as whaling records had suggested, and that they feed mainly between 40 and 50 degrees south. The same page says whaling cut the population from an estimated 30,000 to about 40 by 1920, and that it had recovered to roughly 2,000 by 2009. Against that history, evidence of flexible routes is welcome news for a species still rebuilding. The page adds that tags went on during research voyages in August 2020, August 2021 and July 2022, that a September 2025 study found most New Zealand whales feed in international waters rather than around Antarctica, and that tagging data helped inform an April 2024 policy aimed at reducing the risk of vessel strikes on the population.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.