Humpback whales have been spotted in a Kakadu river. So in a fight with a crocodile, who would win?

Northern Territory Government

Vanessa Pirotta, Macquarie University

In recent months, three humpback whales were spotted in the East Alligator River in the Northern Territory’s Kakadu National Park. Contrary to its name, the river is full of not alligators but crocodiles. And its shallow waters are no place for a whale the size of a bus.

It was the first time humpback whales had been recorded in the river, and the story made international headlines. In recent days, one whale was spotted near the mouth of the river and scientists are watching it closely.

The whales’ strange detour threw up many questions. How did they end up in the river? What would they eat? Would they get stuck on the muddy river bank?

And of course, there was one big question I was repeatedly asked: in an encounter between a crocodile and a humpback whale, which animal would win?

A crocodile partially submerged in a river
The whales swam into a crocodile-infested river.
Dean Lewins/AAP

Scientists double-take

The humpback whales were first spotted in September this year by marine ecologist Jason Fowler and fellow scientists, during a fishing trip. Fowler told the ABC:

I noticed a big spout, a big blow on the horizon and I thought that’s a big dolphin … We were madly arguing with each other about what we were actually seeing. After four hours of raging debate we agreed we were looking at humpback whales in a river.

The whales had swum about 20 kilometres upstream. Fowler photographed the humpback whales’ dorsal fins as evidence, and reported the unusual sighting to authorities and scientists.

Thankfully, two whales returned to sea on their own, leaving just one in need of help. There was concern it might become stranded in the shallow, murky tidal waters. If this happened, it might be attacked by crocodiles – more on this in a minute.

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Experts considered a variety of tactics to encourage the whale back out to sea. These included physical barriers such as nets or boats, and playing the sounds of killer whales – known predators of humpback whales.

But none of these these options was needed. After 17 days, the last whale swam back to sea on its own.

The whale that spent two weeks in the river has recently returned and been spotted swimming around the mouth of the river. It appears to have lost weight – most likely the result of migration. It is now being monitored nearby in Van Diemen Gulf.

Questions are now being raised about the health of the animal, and why it has not headed south for Antarctic feedings waters.

A humpback whale that spent two weeks in the East Alligator River has recently been spotted nearby.
Dr Carol Palmer

So why were whales in the river?

The whales are part of Australia’s west coast humpback whale population, which each year travels from cold feeding waters off Antarctica to warm waters in the Kimberley to breed.

There are various theories as to why they swam into the East Alligator River. Humpback whales are extremely curious, and may have entered the river to explore the area.

Alternatively, they may have made a navigation error – also the possible reason behind September’s mass stranding of pilot whales in Tasmania.

And the big question – what about the crocs?

Long-term, a humpback whale’s chances of surviving in the East Alligator River are slim. The lower salinity level may cause them skin problems, and they may become stranded in the shallow waters – unable to move off the muddy bank. Here the animal might die from overheating, or its organs may be crushed by the weight of its body. Or, of course, the whale may be attacked by crocodiles.

In this case, my bet would be on the whale – if it was in relatively good condition and could swim well. Humpback whales are incredible powerful creatures. One flick of their large tail would often be enough to send a crocodile away.

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If a croc bit a whale, their teeth would likely penetrate the whale’s skin and thick blubber. But it would take a lot more to do serious harm. Whale skin has been shown to heal after traumatic events, including the case of a humpback whale cut by a boat propeller in Sydney 20 years ago. Dubbed Bladerunner, it survived but still bears deep scars.

Humpback whales are very large and powerful. One flick of their tail could send a crocodile away.
Dr Vanessa Pirotta

What next?

The whale sighting continues to fascinate experts. Scientists are hoping to take poo samples from the whale in Van Diemen Gulf, and could also collect whale snot to learn more about its health. However, the best case scenario would be to see the whale swim willingly to offshore waters.

This unusual tale will no doubt go down in Australian whale history. If nothing else, it reminds us of the vulnerability – and resilience – of these marine giants.

The author would like to thank Northern Territory Government whale expert Dr Carol Palmer for her assistance with this article.The Conversation

Vanessa Pirotta, Wildlife scientist, Macquarie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.


Fierce female moles have male-like hormones and genitals. We now know how this happens.


Jenny Graves, La Trobe University

Moles live a tough life underground. As a result, they’ve evolved helpful adaptations, such as excavator-like claws. Female moles in particular have evolved an unusual strategy: high levels of the male hormone testosterone.

This is an evolutionary advantage. It produces stronger muscles for digging and foraging and aggression, to help mothers defend themselves and their young.

Most of the year, female moles look and behave like males. They have masculinised genitals, with no external vagina and an enlarged clitoris. But when mating season comes, testosterone levels drop and a vagina is formed; mating and birth follow.

How they accomplish this remained a mystery for a long time. But now, the complete sequencing of the mole genome has revealed the genetic tweaks underpinning this strange cycle in female moles, by which reproductive organs (gonads) develop and hormones are produced.

Gonads and hormones

Male development in humans and other mammals is determined by chromosomes (the structures within cells of living things that contain genes). Females have two copies of an X chromosome. Males have a single X and a male-specific Y chromosome.

In XY embryos, a gene called SRY on the Y chromosome intervenes in a network of another 60 genes. SRY turns on testis genes and turns off ovary genes to transform a ridge of cells into a testis.

In the testis, one cell type becomes specialised to make sperm and another (Leydig cells) makes male hormones, including testosterone.

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Testosterone is responsible for the most visible sex differences in males, such as bigger bodies, more muscle mass, male genitalia and more aggression. In XX embryos, an alternate pathway makes an ovary, which pumps out oestrogen.

So in mammals, different genetic pathways drive the same patch of embryonic tissue to become either an ovary or a testis. Generally, there’s no in-between.

But female moles have a patch of testis within their ovaries.

An evolutionary balancing act

In 1993, it was discovered the basis for “intersex development” in female moles is a gonad with both ovarian and testicular tissue.

Like other male mammals, male moles have a Y chromosome, bearing the SRY gene which directs testis formation.

Also like other mammals, female moles lack a Y chromosome. Curiously, however, instead of developing ovaries they develop “ovotestes”, with ovarian tissue at one end and testicular tissue at the other.

The ovarian tissue makes eggs and gets larger during breeding, then regresses. The testicular tissue is full of Leydig cells that make testosterone (but not sperm). Outside of breeding season, it expands until it’s larger than the ovarian end.

This explains why female moles have male-like genitalia, and are muscular and aggressive. But how does a patch of testis form in female moles if they have no SRY gene to trigger the process?

Genetic tweaks behind ovotestis development

To look for genetic changes that could allow this to happen, a global consortium of scientists sequenced the entire mole genome.

They found no differences between moles and other mammals in the protein products of the 60-odd genes involved in sex determination. However, they did discover mutations that altered the regulation of two of these genes in female moles.

One difference was found in the DNA sequences of a gene that’s vital for developing testes: FGF9. In all mammals, this gene switches on testis growth in XY embryos and inhibits genes that determine ovarian development.

In females of other mammals, the FGF9 gene is turned off in the absence of SRY, but in female moles it stays on.

Genome sequencing revealed why: a big patch of DNA just upstream of FGF9 is flipped around in moles. This inversion removes the usual control sequences from the gene, allowing it to stay on for longer in XX embryos.

The other gene impacted in female moles is CYP17A1, which codes for an enzyme that’s key to producing androgens (male hormones). In female moles, this gene and its surrounds have two extra copies, which increases testosterone output.

To show these genomic changes were indeed responsible for masculinising female moles, the researchers introduced them into mice, causing sex reversal and higher testosterone levels.

It’s important to note these evolutionary changes are in the regulation of gene activity, rather than in the regulation of protein products — which could compromise other normal functions.

Clownfish (_Amphiprioninae_).
Other than mammals, many marine animals have gender-bending tendencies. Clownfish always begin life as hermaphrodites carrying both female and male reproductive organs. Later in life, males can become female on an as-needed basis to mate with other males.
Istvan/Flickr, CC BY

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What this means for sex and evolution

Since mammals, including humans, develop as either males or females, we’ve been accustomed to regard testis or ovary development in the embryo as strict alternatives, depending on an on/off switch (the presence or absence of the Y chromosome and SRY gene).

But we now know there’s a complex gene network full of checks and balances that is the basis for alternate pathways of sexual development.

There are many studies of human babies born with mutations in one of these genes. This points to a more complex picture of the wiring behind the “switch” responsible for variation in human sexual development.

There are fierce females in other mammal species, too. Female spotted hyenas are bigger and more dominant than males and have male-like genitalia. We don’t know how this change works at a genetic level.

A female spotted hyena in the wold.
The spotted hyena, Crocuta crocuta (also known as the ‘laughing hyena’) is native to sub-Saharan Africa. In females such as this one, the clitoris is shaped and positioned like a penis that can become erect.

The downside of this is that mating is tricky. Cubs are birthed through the female’s narrow phallus. Mothers and/or cubs often die during this fraught process.

So while these larger, more aggressive females rule the hyena roost and get first pick at meals, like most things in nature, it seems this comes at a price.

Big fierce female moles and hyenas remind us the natural world, as always, features unique evolutionary differences — enlightening our view on human variation.The Conversation

Jenny Graves, Distinguished Professor of Genetics and Vice Chancellor’s Fellow, La Trobe University

This article is republished from The Conversation under a Creative Commons license. Read the original article.