Some humpback whales are born in warmer waters. Others are born on the way. That’s what a study in Frontiers in Marine Science seems to suggest, anyway, after showing that hundreds of East Australian humpback whales are actually born mid-migration, while their mothers are still traveling to their established calving and breeding grounds.
“Hundreds of humpback calves were born well outside the established breeding grounds,” said Tracey Rogers, the senior study author and a biology professor at the University of New South Wales, according to a press release. “Giving birth along the ‘humpback highway’ means these vulnerable calves, who are not yet strong swimmers, are required to swim long distances much earlier in life than if they were born in the breeding grounds.”
In fact, the study shows that these calves are sometimes born in the temperate waters around Southeastern Australia, New Zealand, and Tasmania, around 900 miles south of the traditionally assumed area. Challenging the theory that humpback migration is essential for the birth of these whales, the study provides valuable information for protecting humpback whale populations in the future.
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Humpback Whale Mid-Migration Sightings
Every year, Eastern Australian humpbacks travel from the polar waters of the Southern Ocean around Antarctica to the tropical waters of the South Pacific Ocean around northeastern Australia. For a long time, it was thought that this winter migration enabled the birth of these whales, with the whales having to be born in these warmer waters.
“Historically, we believed that humpback whales migrating north from the nutrient-rich Southern Ocean were [traveling] to warmer, tropical waters, such as the Great Barrier Reef, to calve,” said Jane McPhee-Frew, the lead study author and a biology Ph.D. candidate at the University of New South Wales, according to another press release.
But in July 2023, McPhee-Frew spotted a pair of Eastern Australian humpbacks — a mother and a calf — in the temperate waters around southeastern Australia, apparently on their way to their established calving and breeding grounds.
“The calf was tiny, obviously brand new,” McPhee-Frew said in the press release. “What were they doing there?”
Hoping to find out, McPhee-Frew, Rogers, and a team of five other researchers studied hundreds of observations of Eastern Australian humpbacks from around southeastern Australia, New Zealand, and Tasmania. Including information from citizen scientist sightings, scientist surveys, and beach strandings, the team examined 209 observations of calves, including 168 observations of living calves, many of which were made in 2023 and 2024.
Surprisingly, some of the observations were made as far south as Port Arthur, Tasmania, with many of the mothers continuing to travel north with their newborns.
According to the team, these mid-migration births are probably not a new phenomenon, as records seem to suggest that they occurred in the 1800s and 1900s, too, before the collapse of Eastern Australian humpback populations due to commercial whaling.
“I think it’s very likely that this pattern has always existed, but the low number of whales obscured it from view,” McPhee-Frew said in the press release. “The Eastern Australia humpback population narrowly escaped extinction, but now there are [30,000, 40,000, or 50,000] in this population alone. It doesn’t happen overnight, but the recovery of humpback whales, and the return of their full range of behaviors and distribution, just goes to show that with good policies built on good science, we can have excellent outcomes.”
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Protection for Whale Populations
A mother and baby humpback whale swimming in Kiama, New South Wales, Australia. (Image Credit: Vanessa Risku (Instagram: @droning_my_sorrows))
The fact that these calves can be born on their way to the mothers’ calving and breeding grounds means that the purpose of humpback migration is much more of a mystery than typically thought. Indeed, if humpback mothers can deliver babies in temperate waters, why do they travel to tropical waters every year?
Though the study cannot confirm this theory, the warm waters of northeastern Australia may offer other benefits beyond birth. For instance, they might be a potentially safer space for calves to learn and grow, even if they were born elsewhere. Such benefits might make the move worthwhile, the team says, despite the risks of delivering a newborn in the midst of migration.
And there are a lot of risks. Without a newborn, the trip is long, spanning several thousand miles from the South Ocean to the South Pacific Ocean, and straight through some of the busiest swathes of sea.
“This means these vulnerable animals are exposed to risks like boat strikes, entanglements, pollution, and just general public unawareness,” Rogers said in the press release. And adding a calf to the mix merely increases the risk, as newborn humpbacks are slower and weaker than their mothers.
“They have those long, enormous fins that they need to grow into, and they’re not very strong swimmers. So they rest a lot of the time on their mum’s back,” Rogers said in the press release. “It’s heartbreaking to think of these young whales [traveling] through busy ports and dangerous shipping lanes with those long, clumsy fins.”
The injuries on some of the observed newborns stress the need to do more to protect whales as they travel, the team says. Fortunately, with better information about where these calves and their mothers appear, protected areas and awareness campaigns can be better calibrated to save whales of all ages.
“Regardless of the health of population now, we can’t be in a situation where we’re putting any age of whales — especially baby whales — in a situation where they’re getting caught in nets, being exposed to chemicals, being hit by boats and being harassed,” McPhee-Frew said in the press release.
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Article Sources
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Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
