Humpback whales lost up Australian river

These whales were spotted tens of kilometres inland - how did they get there, and can they make it home?
22 September 2020


The tail of a humpback whale surfacing above the water.


A group of humpback whales were spotted this week tens of kilometres off their beaten track, inland along the East Alligator River in Australia’s Northern Territory. Despite the misleading name - there are no alligators in Australia - the river is nevertheless filled with fearsome saltwater crocodiles. So what were the whales doing there, and what will happen to them? Katie Haylor reports...

Katie - Off-duty marine ecologist Jason Fowler, and colleagues, first spotted a group of humpback whales on a fishing trip in Kakadu's East Alligator River in the Northern Territory; which raised quite a few eyebrows, to say the least, as it's the first known instance of this happening.

Vanessa - We first saw these animals up to as much as 20 kilometres up a river in the Northern Territory in Australia; and just to paint a bit of a picture here, we're talking murky, muddy waters. And so when I first saw the picture of a humpback whale, which is an oceanic species, in this murky water, it was something... it was a phenomenal thing.

Katie - That's Sydney-based marine scientist Vanessa Pirotta. Now two of the whales, it's thought, have since swam back out to sea; but at least one remains in the river. And the worry is if it gets stranded in the shallower water.

Vanessa - Is it going to be able to get out? So the main reason that they're probably in there is - I should point out this has never happened before - but maybe one of the animals took a wrong turn and ended up in this area. The humpback whales are generally in the Kimberley region, which is the North West of Australia, each and every year to breed and have their babies. And then now it's their time to be heading back south, down to Antarctica, where they're going to spend the summer feeding; but let's hope that this one remaining whale has the opportunity to do just that.

Katie - Being in a tidal river is rather different to being in the sea. So how might the whale be doing?

Vanessa - They do use sound to listen and to vocalise, and to talk to each other. Now this whale, because they're non-echolocators, may be reliant on visual cues, so simply having a little look around or trying to see where there's a space to swim in that's safe. So there's a whole number of things that would probably be going through this whale's mind, and without anthropomorphising it or putting a human spin on it, I'm sure that this animal might be doing circles. At least on Friday there'll be a team going up just to have another look at it, just to see what it's doing, and to see if it's made any progression in its movements.

Katie - Stranding is a real risk. And up in the Northern hemisphere, Southampton University's Clive Trueman told me why this is so dangerous for a whale.

Clive - Water would normally be supporting the weight of the organs and the weight of the animal, so when it strands, that can compress the lungs and damage the internal organs. At the same time, if a whale is stuck and the tide is coming in and out, almost paradoxically the whale can drown because it can't lift itself off of the sandbank, and then water can get into the blowhole and drown it.

Katie - So what tools do scientists have available to encourage a 12-plus-metre whale to do anything?

Vanessa - There's a couple examples that I can run through, one being creating a physical barrier with boats so the animal will simply move away, it's hoped; in some cases that hasn't worked in the past where the animal has simply gone onto boats. You could use acoustics such as banging on, physically banging on vessels, which is really not too nice for a whale. Some have suggested using killer whale playback sounds, which is the predator of the humpback whales; but again, a lot of these are potentially going to induce stress, so an expert team will have to weigh up what options are potentially going to be put on the table to see if it's worth inducing these kind of reactions to then have a favourable result, which would be the animal turning directions and heading out to sea.

Katie - As the name of the river suggests, the whale isn't the only thing in East Alligator river. Clive again.

Clive - Saltwater crocodiles are fantastic animals and extremely intimidating, but probably not a risk to a 16-metre adult humpback whale; unless, again, the whale is stranded. And if the whale is stranded and stuck then you could imagine the crocodiles could pose an additional risk.

Katie - At the time of recording we don't yet know the humpback whales fate. But could there be a positive here? Could having enough whales to be able to get lost on a migration indicate that population numbers are doing well?

Vanessa - We definitely know this population is doing quite well. In fact, this is one of the largest humpback whale populations in the world. So what I'm trying to say is the removal of one individual in a very large, well growing population is not going to limit the recovery of this species or essentially the population, which is a positive thing.

Clive - Humpback whales are certainly recovering from the effects of whaling faster than many other baleen whales. What would be fascinating to know is whether there are cultural records, indigenous records, tribal stories of humpback whales in rivers from the time before European hunting. And it would be absolutely fascinating if that's true.

Since this story first aired, the remaining whale has safely made it out of the Alligator River and back to the open sea.


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