Common Dolphin, Gregory 'Slobirdr' Smith CC BY-SA 2.0

On 27 June 2021, the Scottish Government launched an investigation into 'sonic torture' of porpoises resulting from the use of acoustic deterrent devices by the salmon industry to control seals there [1]. 

Dolphins and porpoises experience sound differently — more intimately — than we do. As much as language is an important part of how we relate to one another, dolphins use sound for that and for so much more. Their language is in the form of clicks and squeaks, and they use sound waves for echolocation, or sonar, to “see” the distance, shape, and size of objects. They use echolocation for communicating, navigating, social cohesion, and finding food. They orient in their world based on nuances of sound the way we rely on nuances of vowels, nuances of scent, or nuances of flavour. Imagine if those were overpowered by machinery and acoustic harassment devices, and there was no escape. 

Moreover, sound travels differently underwater compared to how it moves on land. Sound travels farther underwater, and its source direction can be difficult to identify. If you’ve ever been scuba diving, you may have experienced hearing a boat engine starting up and it sounded like it was right on top of you but you didn’t know which direction, only to surface and discover that it was quite a distance away. So again, imagine what it must feel like for a dolphin just trying to take a nap or trying to find fish to eat. 

Here in Tasmania, sound pollution is already a problem for humans. Once residents awoke here to the tweeting and squawking of birds, relaxed with a cup of tea, gazing out over the stillness on the water, with the nights so quiet that they could almost hear the stars shimmering. And then the unimaginable happened. Heavy industry moved in. Their view is now salmon cages, boats and ships coming and going, and bright lights all night. Curtains now cover the windows. Ear plugs are not enough. Pillows over the head are not enough. The thrum of engines is 24/7. The vibration is inescapable: sitting in a chair or on the toilet, you feel it through your bottom, you lean on the kitchen counter and feel it through your arm, you lay on your bed and feel it through your whole body. And the ever-present hum is occasionally punctuated by the only-slightly muffled sound of underwater bombs, used to deter seals away from the fish pens. Your only moments of peace are when you leave, but then you are consumed by a feeling of impending doom as you round the bend coming home. 

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As hard as it is for people to deal with this intrusion, it is much harder for dolphins. People can use ear plugs, wear noise-canceling earphones, or turn up the music. We shouldn’t have to, but the point is that we can. Those options obviously are not available to dolphins. 

Below are exerpts from a speech to an Australian Senate Inquiry on proposed changes to federal environmental protection legislation. It captures the frustration at our dithering while species — the subjects of, and meant to be protected by, the legislation — are falling through the cracks. Click here to hear the whole speech on The Science Show on ABC Radio National. 

A species of dolphin endemic to southeastern Australia -- that is, found nowhere else in the world -- is threatened by salmon farming in Tasmania. But this is not 'just threatened' in the typical ecological sense, this is oppressed, harassed, disabled, and quite possibly eradicated, in the pursuit of profit. 

This dolphin was only named and classified as a new species in 2011 [2]. It was given the scientific name Tursiops australis, and is also known commonly as the Burrunan Dolphin. It is the common inshore dolphin in two capital cities, Melbourne and Hobart, and it is also found in the Gippsland Lakes — if you see a dolphin, it’s probably this one! But its three resident populations are all in great peril due to urban runoff,  disease, fluctuations in food, boat strikes, and heavy metal poisoning.

In the 1970s, Hobart's Derwent Estuary held the shocking title of being the world’s most polluted estuary [3], because of the heavy metals. Today, they are being resuspended by an unfortunate process of water chemistry that unbinds the molecules from sediments when the dissolved oxygen is very low — the inevitable condition created by salmon farming. Research in Victoria in 2014 found that this species had the second highest mercury content of all the dolphin species studied [4]: chronic exposure is thought to suppress immunity and interfere with neurochemical pathways. In eastern Victoria’s Gippsland Lakes, in 2021, this species lost 20% of its population from a skin disease that’s similar to 3rd degree burns, and almost every year it is in competition for food against increasing swarms of jellyfish: jellyfish eat the eggs and larvae of small fish such as pilchards, then the dolphins have nothing to hunt [5]. In Hobart’s Storm Bay, it used to be common – this is the species in the iconic photo for Pennicott Adventure Tours – it is one of the first things visitors see at the Hobart Airport — but there’s not a single study on this species here, we know nothing about it, except that locals see it less often in the last few years.

In Tasmania, however, by far its biggest threat is Salmon Farming. Salmon farming is — in practice — largely exempt from environmental legislation, simply because the State Government looks the other way. Salmon farming has turned quiet bays into unrelentingly noisy industrial sites, where big ships and heavy machinery are operating at all hours. Imagine what this industry, which is creating a serious mental health crisis for human locals, is doing to dolphins that use echolocation in all aspects of their daily life. 

And on top of that deafening thrum, the salmon industry sets off tens of thousands of underwater ‘cracker bombs’ a year to deter seals. In 2018, this number was reported to be almost 40,000 [6]. Between January 2018 and January 2021, Tassal alone detonated more than 55,000, Huon Aquaculture 16,000, and Petuna 3,500 [7]. These explosives shatter bones, rupture eardrums, and herniate brain tissue, so imagine what they do to the echolocation of dolphins. 

In Victoria, this dolphin is now listed as Critically Endangered under the Victorian Flora and Fauna Guarantee. However, in Tasmania, it has no such listing. Instead, it is collateral damage of a state government decision to grow the salmon industry at all costs. It is untenable to put the state government, which is responsible for growth, in oversight of the casualties of that growth. This is the Fox guarding the Hen House!  

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Back to the Scottish investigation. It followed on from a recent modeling study there, which found that porpoises would likely sufferer auditory impairment as collateral damage from acoustic seal deterrents [8]. This study focused on 'electronic fences', which give intruding seals a feeling of discomfort; however, these devices also send sound waves great distances, where they can have unintended consequences. In Tasmania, a feeling of discomfort from an electronic fence is not the problem, it's more the tens of thousands of underwater bombs and constant ship noise, none of which can possibly be good for dolphins. 

Here's what we need in Tasmania — urgently:

(1) The State must accept that this species occurs here, and that it is Critically Endangered in its two other known populations. It must be listed for greater protection here. 

(2) Research must be carried out to understand exactly what the nature and extent of impact is on this dolphin species (and presumably other cetaceans using the area) from salmon farming activities.

(3) Research into its population dynamics must be performed to assess a baseline for perceiving decline or recovery. 

 

REFERENCES

[Click here to go to Dolphin References]

 

For a wealth of interesting info on the Burrunan Dolphin, have a look at the Marine Mammal Foundation website!

With every bite of salmon, we are giving our implicit consent to cruelty