Humpback whales can give birth while migrating thousands of miles

Yahoo

20-05-2025

Humpback whales (Megaptera novaeangliae) are master migrators. Some populations of this baleen whale species travel upwards of 5,000 miles per year from colder waters to feed, towards warmer tropical waters where they give birth and care for their calves.
However, new research on a population off Australia's eastern coast indicates that their trips to more balmy waters are not as essential to calving as biologists thought. Calves in this population can actually be born in colder waters near New Zealand or Tasmania–about 932 miles further south (1,500 kilometers) than previously known. Understanding this pattern could challenge some long-held beliefs about humpback migration and improve protection areas to help these baby whales. The findings are detailed in a study published May 20 in the journal Frontiers in Marine Science.
'Hundreds of humpback calves were born well outside the established breeding grounds,' said Tracey Rogers, a study co-author and marine ecologist at the University of New South Wales in Australia. '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 the Northern Hemisphere, humpback whales like those found on the east coast of the United States and Canada, typically migrate from colder feeding in the Northern Atlantic Ocean in the summer and south to the Caribbean for the winter to breed and calf.
For Southern Hemisphere humpbacks like those off the coast of Eastern Australia, the directions are flipped because of the equator. They travel from their frigid feeding grounds in the Southern Ocean around Antarctica, north towards the Pacific Ocean in Australia to breed, calve, and care for their young.
Finding this new baby whale hotspot arose due to study co-author and University of New South Wales Ph.D candidate Jane McPhee-Frew's extracurricular work as a marine guide.
'In July 2023, during a whale-watching tour, I encountered a mum and calf at the mouth of Newcastle Harbor—the busiest shipping port in Eastern Australia,' said McPhee-Frew. 'The calf was tiny, obviously brand new. What were they doing there? But none of my tourism colleagues seemed surprised.'
This new sighting piqued researchers' interest and they began investigating the calving range for humpback whales located around Australia and New Zealand. They used data from citizen science observations, government surveys, and reported strandings. New Zealand's Department of Conservation Cook Strait Whale Project supplied data from migration surveys, and Australian state wildlife departments supplied information on strandings dating all the way back to 1991.
The team found 209 records of newborn calves (including 11 births), 41 strandings, and 168 observations of live calves, representing at least 169 individual whales. They also had data on the direction of travel for 118 whales, which showed the whales were continuing to migrate north after delivery.
'Humpback whale populations undertake extensive long-distance migrations from the Southern Ocean to breeding grounds in the tropics,' said study co-author Adelaide Dedden of the National Parks and Wildlife Service, Australia. 'They rely heavily on body reserves from an enormous amount of Antarctic krill to support the physiological costs of the journey and reproduction.'
The highest-latitude calf was found at Port Arthur, Tasmania–about 932 miles further south than it was believed that humpbacks could calf.
When they compared these observations taken over the last decade with historical texts and whaling logbooks, they say that calves born during migration were observed more often before the population crashed due to hunting. Humpback whale numbers in Australia crashed during the peak of the whaling industry, particularly during the 1960s and 1970s.
'I think it's very likely that this pattern has always existed, but the low number of whales obscured it from view,' said McPhee-Frew. 'The Eastern Australia humpback population narrowly escaped extinction, but now there are 30, 40, 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.'
For all migratory species, these epic journeys cost a great deal of time and energy. The energy expenditures can leave their young vulnerable to predators. While this particular study can't answer why humpback whales risk migrating if they can give birth further south, it's possible that other factors are driving migration. The benefits of delivering in tropical waters might outweigh the risks of having a potential calf born along the way.
While the data provided by Western Australia's Department of Biodiversity, Conservation, and Attractions pinpointed a possible nursery area in Flinders Bay, it's likely that most calves are born much further north in the tropics.
[ Related: Humpback whales use bubble-nets as 'tools.' ]
According to the team, there are several conservation implications in these findings. Some of the observed calves were injured, so expanded protected areas, awareness campaigns about protective measures boaters and the general public can take, and more research into the habitats that humpbacks use while migrating are critical to safeguarding the calves.
'This study was based on opportunistic observations,' cautioned McPhee-Frew. 'This data is excellent for answering questions like, 'are there newborn whales here?' But we can't stretch the interpretations too far. It might appear that we see more calves the further north we go, or that we have seen more over time. But it could be that there are more people whale-watching in the north, or more cameras and social media sharing in recent years.'
'We can only document what we see,' added study co-author Vanessa Pirotta of Macquarie University in Australia. 'Perhaps there are things happening in our ocean that we are yet to find out.'