Program: Lab Notes: Why do whales beach themselves?

News grab: A pod of false killer whales rapidly losing the battle to survive.

News grab: There are frantic efforts to save more than 150 whales stranded on beach.

News grab: There is a desperate rescue attempt underway on WA's south coast after a pod of pilot whales beached themselves.

Belinda Smith: Every now and again, dozens or even hundreds of perfectly healthy looking whales strand themselves on a beach. And despite people's best efforts, many, if not all of them, will die. The most recent Australian mass whale stranding to make headlines was in February 2025, involving 157 false killer whales in northwest Tasmania. Around 90 of those whales had to be euthanised. So why do thousands of whales beach themselves every year? And why do they seem to do it at the same places? Hi, I'm Belinda Smith and you're listening to Lab Notes, the ABC Radio National show that dissects the science behind new discoveries and current events. To tell us what scientists know and don't know about whale mass strandings is Kate Sprogis, a marine mammal ecologist at the University of Western Australia's Albany campus. Albany, so that's a very famous spot for whale watching, isn't it?

Kate Sprogis: Yeah, it's on the south coast of Western Australia and we're so lucky to have multiple species that come visit our coastline.

Belinda Smith: I'm guessing though that with whales comes whale strandings, right?

Kate Sprogis: Yes, so our coastline on the south of Western Australia, but also the southwest of Western Australia, is one of those sort of hot spots that whales do strand. And this is typically our toothed whales, so those whales that have teeth in their mouth. So they're not generally the baleen whales, so baleen whales have baleen and they filter feed. We do get strandings of these animals, but the actual mass strandings where we've got more than two animals, it could be three animals, it could be ten animals, it could be all the way up to like 400 animals that mass strand, that's the toothed whales.

Belinda Smith: So a mass stranding is just more than two, I never even considered what a mass stranding was.

Kate Sprogis: Yeah, so it's not a mum and her baby, so it's not a mother calf, but if it's more than two animals, it's classified as a mass stranding. Because generally what happens is there might be a single stranding of an animal and that might be just a sick animal or an old animal and that's why it's washed up on shore. Whereas a mass stranding, they're the complicated, complex ones.

Belinda Smith: Have you been to many mass strandings?

Kate Sprogis: Oh, unfortunately I've been to a few. Yeah, so the largest one I've witnessed was off Toby's Inlet off Dunsborough, the south west of Australia. And there was about 160 longfin pilot whales that stranded and about 30 that ended up passing away. It is quite a sight to see these beautiful animals on the beach. They're big and they're black and they have white markings on them. So they have nice white saddle patches behind their dorsal fin and they have a bit of white from their eye. And to me when they're on the beach, they just look like a plastic mould of a toy but in a giant size version of that. You sort of just stand there and scratch your head and go, why are you here?

Belinda Smith: And that's the million dollar question. Why have these massive marine mammals decided to beach themselves in such huge numbers? And generally speaking, it's a couple of species of whale that does this.

Kate Sprogis: Pilot whales and false killer whales, they are our most commonly stranded whales off Australia.

Belinda Smith: And there are some stranding hotspots and these locations might provide some clues. In

Kate Sprogis: south western Australia, some of our locations where these animals strand are Geograph Bay, Flinders Bay, Chains Beach and all these are basically bay types. So they're shallow water, they're a little bit complex so it makes you ask the question of, okay, why are they stranding in these locations? And maybe it has something to do with they're evolved to be a deep water species. They're used to diving really, really deep depths, 600, 1000 metres depth. Wow. Using their echolocation in really deep waters because they hunt squid. Whereas they're not evolved to be a shallow coastal water species where the noise rebounds off everything. So the rocks, the sand, the surface, the bottom. And that's when they might get into a bit of trouble.

Belinda Smith: Hmm. Right, okay. So they might get confused by the sound bouncing around them. I guess that would stress them out as well.

Kate Sprogis: Yeah, so that's one of the theories. So one of the reasons might be they're just in the wrong place and they get confused, they get disorientated and they're not sure which way to go. They get stressed. They're a really tight-knit family so they all stay together and then it's a bad outcome.

Belinda Smith: Because pilot whales have a matriarchal social structure, the mother and the sisters and the cousins and the kids and everyone is always hanging out together, they might follow a whale from their social group into a shallow area and then all get stranded.

Kate Sprogis: So another reason why they might strand is because they're actually sick. So they might actually be sick, they might be unhealthy, they might have an illness, a disease, and that is when maybe they're stranding for a reason. And so that's when if animals are sick, that's when it's really important to do an animal necropsy. And that's like a human autopsy, finding out why the individual has passed away. And so we call it a necropsy. And so it's finding out as much information as we can from the animal to find out if it is sick or not.

Belinda Smith: What else might drive whale strandings?

Kate Sprogis: Yeah, so another reason why whales might strand is due to environmental factors. So there's a lot going on out in the deep ocean. So we've got different prey, we've got different sea surface temperatures, we've got El Nino and La Nina. These might cause marine heat waves, it might cause cooler temperatures, this might change the prey abundance and the prey distribution. And so these movements of the prey and the changes in the ocean might affect these deep water species to come into shallower waters. And then that's when they might get confused and disorientated and end up on a beach.

Belinda Smith: And we've been polluting the oceans with a lot of noise as well, haven't we?

Kate Sprogis: Yeah, so with human activities, one of the main causes of disturbance to animals is underwater noise. And these animals are highly auditory species, so they rely on sound to understand their environment. And you've got to remember that a lot of the time it's dark. It's nighttime, it's deep dark waters, but it might just mask out their sound. So they might not be able to communicate with each other as easily. But what they have found for different species, so not necessarily the longfin pilot whales and the false killer whales, but the beaked whale is the one that sometimes might end up stranding because of navy sonar or seismic surveys. Basically because they get disturbed, they stress out and they surface too quickly and they end up getting the bends. So there's clearly

Belinda Smith: loads of variables here and it's very hard to pinpoint exactly why these strandings are happening. But in 2023, nearly 100 longfin pilot whales stranded at Chaynes Beach, east of Albany. But before they did, the whales displayed some really weird behaviour. Parks

Kate Sprogis: and Wildlife called me and they said, oh Kate, is this normal? Is this behaviour normal? What's happening? We've got some longfin pilot whales and they're really, really close together and they're huddling in a very tight-knit group. And that's when we basically said, oh, that does not sound normal. That's not natural behaviour. They're not normally that close and tight together. And prepare for a stranding just in case it might happen. It might not happen. It might happen the day after. It might happen in a week. We had no idea because it's generally not something that we see. So we reached out to international colleagues around the world and we asked our colleagues, has anyone else seen this huddling behaviour? And only a handful have. And so it might actually be a precursor to strandings, which is huge information for us as researchers, but also for stranding networks and governmental groups who are alerted to these strandings because they then have to manage the mass stranding event.

Belinda Smith: At that point, is there anything you can do to stop them stranding?

Kate Sprogis: Yeah, that's a really good question. There are some groups internationally and in Australia that if you can get there on time quickly enough, that you can actually try and guide the animals back out to deeper water. And sometimes this does work, but it really depends on why they're stranding. So if they're actually sick and they have a disease or they're ill in some way, they might actually be stranding because they're sick. And so maybe then trying to push them back out into the deep ocean is going to cause the animals more stress. And from an animal welfare point of view, that's not very nice for sick animals. Whereas if they're actually healthy animals and they're disorientated, then that is the big question of, okay, can the authorities get there in time before they strand or as soon as they strand? So that the stress of stranding is not too much upon them, that can they guide them back out to deeper waters? And they have done this successfully in some locations, but it is logistically challenging, as you can imagine. In the

Belinda Smith: future, I know it's impossible to say, but I don't know, will we see more mass strandings? Yeah.

Kate Sprogis: So I predict that with, say, more marine heat waves and changes in the ocean, that because we're getting more intense La Ninas and more intense El Ninos this is when we get the extremes in the ocean. And this then affects the prey, it affects the whole ecosystem. And that's when we get our mass strandings. And so I do predict that we will be getting more in the future.

Belinda Smith: I'm Belinda Smith. This episode was produced on the lands of the Wurundjeri and Menang Noongar people. Fiona Pepper's the producer and it was mixed by Angie Grant. We'll catch you next week.