The beaches of Sydney’s Royal National Park have been disrupted by a pungent odour. And its source is drawing in more than just seagulls.

A 25-tonne sperm whale is rotting on the rock platform of Era Beach. This spectacular sight is drawing in curious spectators and hungry predators.

The humans are keen for a photo op. The predators are drawn by the potential meal.

The lifeless whale may look inviting – to some. But it might be more dangerous for us humans to get close than you may suspect.

How often do whales wash up on shore?

This particular cetacean is likely to have died at sea some weeks ago. But unfortunately, many more whales are being stranded on rock platforms and beaches across the globe.

Strandings are not rare in Australia or New Zealand. Southeast Australia alone recorded 639 strandings between 1920 and 2002. The rate of whale strandings globally also seems to be climbing as some whale populations are recovering and there are more people out in nature to spot them.

Australia has also seen some of the largest mass strandings on record (it has the unenviable title of being a global hotspot). These include 470 long-finned pilot whales beached at Tasmania’s Macquarie Harbour in 2020.

However, a single large carcass, like the Era Beach sperm whale, is more typical – and the one people are more likely to see.

It’s quite a spectacle

A decomposing whale is quite the spectacle. It’s a fascinating and morbid sight. According to one media report today:

Thin strips of flesh hang down like rotten tinsel, swaying in the wind. Glistening fluid trickles on to the stone where insects buzz.

Unsurprisingly, beached whales draw in curious people involved in both citizen science (when the public collects and analyses data about the world around us) and for the prospect of a grisly social media shot.

But frolicking around a huge dead beast has potential dangers. And in this case, the environment where the whale rests is the most significant factor.

The massive whale is decomposing on a rock shelf next to the ocean, with tides, waves, and swells. Standing on a rock ledge inspecting a whale means you’re not paying attention to your surroundings. This is how you can find yourself unintentionally entering the ocean.

The ocean may appear calm and forgiving when you first step onto that ledge to inspect the whale, but conditions can change rapidly.

Read more: The ocean can look deceptively calm – until it isn’t. Here’s what ‘hazardous surf’ really means

Then come the sharks

People aren’t the only ones going for a stickybeak at this whale. Bull, tiger and great white sharks are scavengers. To them, a fresh whale carcass is like an enormous buffet. The blobs of fat floating in the water around the whale are, essentially, canapes.

One study used drones to see how the behaviour of 55 white sharks off the coast of New South Wales changed near a stranded whale. They swam faster. Sharks near a stranded whale also tend to be larger on average – possibly because big sharks muscle smaller ones out the way.

These hazards are why many beaches near the stranded whale have been closed as a precaution. NSW National Parks and Wildlife Service warns people not to enter the water due to increased shark activity.

What is that smell?

A gigantic decaying whale, warmed by the midday sun, and kept moist by sea spray, is basically a huge vat of bacteria.

As microbes break down proteins and fats inside the carcass, they release a cocktail of volatile compounds. These include hydrogen sulfide (the smell of rotten eggs), methanethiol (rotting cabbage) and ammonia. Then there’s the aptly named putrescine and cadaverine, the compounds that give corpses their distinctive stink.

So it’s probably best not follow your nose on this occasion. The smell of a rotting whale carcass can be so bad, it can make you vomit. And as waves wash over the carcass or it bloats and ruptures, tiny aerosols are released into the air. These can carry bacteria and pathogens, along with that putrid smell that can drift far beyond the carcass itself.

Marine animals can also carry zoonotic diseases (illnesses that pass from animals to humans). So it’s important not to touch the carcass.

Watch out! It might explode

And who wants to be near when the ticking time bomb goes off? Yes, whale carcasses can explode.

This happens when there’s the natural build-up of gases as the whale decomposes. This is one reason authorities prefer to send the carcass back to sea, if feasible.

So, a selfie that involves climbing onto a whale carcass is a genuinely bad idea.

Samuel Cornell does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.