THE BLOG

Why Do Whales Strand?

03/02/2016 21:32 GMT | Updated 03/02/2017 10:12 GMT

The most frightening experience I've ever had underwater was not being bitten by a shark, or charged by a monster crocodile, nuzzled by an anaconda, or swimming face first into a hippo in the Okavango. Instead, it was diving under a fishing boat that was catching squid at night. My cameraman's torch cut like a light sabre through the blackness, as thousands of pint-sized market squid bounced between our hands like little luminous bath toys. The clonking of the boat propeller seemed to be right on top of us, despite the fact that they were 30 metres above. And then the whole world exploded. A bang so loud it seemed to be inside my head, then a pressure wave that reverberated through every air space in my body.

Disorientated and deafened I would have made a lethal dash for the surface if cameraman Simon hadn't grabbed a hold of me. The fishermen above were throwing fishbombs; half sticks of dynamite into the water to scare sealions out of the squid nets, and the properties of water meant the sound and pressure wave traveled at great speed and without dissipating in force. Another went off, and another; it felt like we were being carpet-bombed. It was terrifying, I have never felt such dread and claustrophobia. Ears ringing, heads throbbing we had to get out of the water and fast.

This bombing is just one of the ways we humans are filling the deep with our noise pollution. The 'Silent World' that Jacques Cousteau explored in the 1950s was a bastion of quiet - the crackling of shrimp and dolphin whistles the only soundtrack, and whales using infra and ultra sound would have communicated with each other across oceans. But everything has changed.

Most modern boats have depth and fishfinders that send eternal pings off into the blue. City-sized cruise and cargo ships have vast propellers you can hear from miles away. Seismic surveys for oil, gas and undersea minerals create pulses of intense noise. Pipelines and radio signals hum and buzz, and offshore construction building wind farms and bridges pound the depths with pile driving, pumping and explosives. It's a marine nightclub playing non-stop happy hardcore FM, an aquatic construction site with a never-ending jackhammer baseline.

So how must it be for marine mammals who can't escape the water? Who rely entirely on sound as their primary sense, and have aural systems so sensitive they make our little ears seem utterly pathetic? Special Forces recruits are played white noise as the most effective form of torture (for 45 minutes only), and reportedly playing inmates at Guantanamo 'Barney the dinosaur' on a loop, was as effective as waterboarding. Have we turned our once quiet oceans into a nonstop earworm of noise that befuddles marine mammals, driving them insane, driving them to strand themselves on our beaches?

The recent beaching of sperm whales on our east coast, and simultaneously in Europe, has once again called attention to undersea soundscapes. Sperm whales are very special creatures, possibly more dependent on acoustics, and more sensitive to it than any other animal in the sea. They generate concentrated bursts as biosonar, which bounce back off the environment and objects in it, before being received and processed as vibrations through the whale's jawbone, then transmitted to the inner ear. When you're in the water with a sperm whale you can feel its sounds reverberating through your body in pulses. To get a crude sense of how biosonar works, close your eyes, start making a clicking sound with your tongue and get a pal to wave their hand in front of your face. You'll be able to tell when their hand is there, due to the more dead, close sound of the echo.

Some visually-impaired people have trained this capacity to such an extent that they can resolve fine detail and manage to find their way around. But this is an unspeakably crude simulacrum of the sperm whale's supersense. They can not only build up a 3D picture of their world based on sound, but in concentrated blasts can use sound as a weapon to stun their giant squid prey. These blasts sound like someone whacking a hammer on an iron pipe, and could be the loudest sounds in nature - at least 220 decibels. A cameraman I was working with whilst diving with sperm whales, had on an earlier trip inadvertently got in between a male and the female he was courting. The male hit him with a blast of sound that - in his words - turned him to jelly in the water, and caused him the most exquisite full body pain he has ever experienced. The systems they have for receiving and processing the echoes that bounce back are just as sensitive.

The first hypothesis of why the whales recently stranded here and on the continent, is that they strayed from their preferred deeper waters (sperm whales hunt squid in water that is often several miles deep) into the much shallower North Sea, and their biosonar became confused. A comparatively shallow sandy bottom, and loads of ambient noise from the busy shipping lanes caused them to become disorientated and to inadvertently swim into too shallow waters. Once they had beached on the high waters of a spring tide, there would be no chance of refloating them.

Could there be any more sinister cause? If a sperm whale can paralyse a giant squid with a burst of 220 decibels, what can blasts of active sonar up to 245 decibels do? Active sonar has been implicated in numerous whale strandings, with a range of species beaching in large numbers following submarine military testing exercises. The US Navy has admitted its high intensity sonar caused beaching of beaked and minke whales in the Bahamas. Fourteen beaked whales that began stranding in the Canary Islands four hours after naval exercises were studied and found to have 'severe, diffuse congestion and haemorrhage, especially around the acoustic jaw fat, ears, brain, and kidneys. Gas bubble-associated lesions and fat embolism were observed in the vessels and parenchyma of vital organs.' The latter effects were hypothesised to be injuries relating from the whales surfacing too quickly. Essentially, they got what divers call 'the bends'. A study by the Space and Naval Warfare Centre in the US linked 39 beaked whale mass stranding events in the modern era to naval activities, (although 87 other events had no reason to be linked). Beaked whales and blue whales have been proven to change their behaviour, stop feeding and move rapidly away in response to simulated navy sonar.

There is no reason at present to think that this latest sperm whale stranding is due to nefarious causes. Necropsies may tell scientists more. It could well end up being nothing more than misadventure as the bachelor pod got lost, the social nature of the beasts causing them to follow their fellows into tragedy. What is certain, is that the silent seas are quiet no longer, and in oceans filled with anthropogenic anthems, a whale's supersenses, could eventually be their undoing.