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Tasmania’s salmon industry detonates underwater bombs to scare away seals – but at what cost?


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Benjamin J. Richardson, University of TasmaniaAustralians consume a lot of salmon – much of it farmed in Tasmania. But as Richard Flanagan’s new book Toxic shows, concern about the industry’s environmental damage is growing.

With the industry set to double in size by 2030, one dubious industry practice should be intensely scrutinised – the use of so-called “cracker bombs” or seal bombs.

The A$1 billion industry uses the technique to deter seals and protect fish farming operations. Cracker bombs are underwater explosive devices that emit sharp, extremely loud noise impulses. Combined, Tasmania’s three major salmon farm operators have detonated at least 77,000 crackers since 2018.

The industry says the deterrent is necessary, but international research shows the devices pose a significant threat to some marine life. Unless the salmon industry is more strictly controlled, native species will likely be killed or injured as the industry expands.

pile of grey and white fish
Tasmanian salmon farming is a billion-dollar industry.
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Protecting a lucrative industry

Marine farming has been growing rapidly in Tasmania since the 1990s, and Atlantic salmon is Tasmania’s most lucrative fishery‑related industry. The salmon industry comprises three major producers: Huon Aquaculture, Tassal and Petuna.

These companies go to great effort to protect their operations from fur seals, which are protected in Australia with an exemption for the salmon industry.

Seals may attack fish pens in search of food and injure salmon farm divers, though known incidents of harm to divers are extremely rare.

The industry uses a number of seal deterrent devices, the use of which is approved by the government. They include:

  • lead-filled projectiles known as “beanbags”, which are fired from a gun
  • sedation darts fired from a gun
  • explosive charges or “crackers” thrown into the water which detonate under the surface.

In June this year, the ABC reported on government documents showing the three major salmon producers had detonated more than 77,000 crackers since 2018. The documents showed how various seal deterrent methods had led to maiming, death and seal injuries resulting in euthanasia. Blunt-force trauma was a factor in half the reported seal deaths.

A response to this article by the salmon industry can be found below. The industry has previoulsy defended the use of cracker bombs, saying it has a responsibility to protect workers. It says the increased use of seal-proof infrastructure means the use of seal deterrents is declining. If this is true, it’s not yet strongly reflected in the data.



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salmon farm infrastructure in water
Seal deterrents are deployed to protect salmon farm operations.
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Piercing the ocean silence

Given the prevalence of seal bomb use by the salmon industry, it’s worth reviewing the evidence on how they affect seals and other marine life.

A study on the use of the devices in California showed they can cause horrific injuries to seals. The damage includes trauma to bones, soft tissue burns and prolapsed eye balls, as well as death.

And research suggests damage to marine life extends far beyond seals. For example, the devices can disturb porpoises which rely on echolocation to find food, avoid predators and navigate the ocean. Porpoises emit clicks and squeaks – sound which travels through the water and bounces off objects. In 2018, a study found seal bombs could disturb harbour porpoises in California at least 64 kilometres from the detonation site.

There is also a body of research showing how similar types of industrial noise affect marine life. A study in South Africa in 2017 showed how during seismic surveys in search of oil or gas, which produce intense ocean noise, penguins raising chicks often avoided their preferred foraging areas. Whales and fish have also shown similar avoidance behaviour.

The study showed underwater blasts can also kill and injure seabirds such as penguins. And there may be implications from leaving penguin nests unattended and vulnerable to predators, and leaving chicks hungry longer.

Research also shows underwater explosions damage to fish. One study on caged fish reported profound trauma to their ears, including blistering, holes and other damage. Another study cited official reports of dead fish in the vicinity of seal bomb explosions.



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dolphin jumps out of waves
Man-made noise can disturb a variety of marine animals, including porpoises.
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Shining a light

Clearly, more scientific research is needed into how seal bombs affect marine life in the oceans off Tasmania. And regulators should impose far stricter limits on the salmon industry’s use of seal bombs – a call echoed by Tasmania’s Salmon Reform Alliance.

All this is unfolding as federal environment laws fail to protect Australian plant and animal species, including marine wildlife.

And the laws in Tasmania are far from perfect. In 2017, Tasmania’s Finfish Farming Environmental Regulation Act introduced opportunities for better oversight of commercial fisheries. However, as the Environmental Defenders Office (EDO) has noted, the director of Tasmania’s Environment Protection Authority can decide on license applications by salmon farms without the development necessarily undergoing a full environmental assessment.

Tasmania’s Marine Farming Planning Act covers salmon farm locations and leases. As the EDO has noted, the public is not notified of some key decisions under the law and has very limited public rights of appeal.

Two relevant public inquiries are underway – a federal inquiry into aquaculture expansion and a Tasmanian parliamentary probe into fin-fish sustainability. Both have heard evidence from community stakeholders, such as the Tasmanian Alliance for Marine Protection and the Tasmanian Conservation Trust, that the Tasmanian salmon industry lacks transparency and provides insufficient opportunities for public input into environmental governance.

The Tasmanian government has thrown its support behind rapid expansion of the salmon industry. But it’s essential that the industry is more tightly regulated, and far more accountable for any environmental damage it creates.



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In a statement in response to this article, the Tasmanian Salmonid Growers Association, which represents the three producers named above, said:

Around $500 million has been spent on innovative pens by the industry. These pens are designed to minimise risks to wildlife as well as to fish stocks and the employees. We believe that farms should be designed to minimise the threat of seals, but we also understand that non-lethal deterrents are a part of the measures approved by the government for the individual member companies to use. If these deterrents are used it is under strict guidelines, sparingly, and in emergency situations when staff are threatened by these animals, which can be very aggressive.

Tasmania has a strong, highly regulated, longstanding salmon industry of which we should all be proud. The salmon industry will continue its track record of operating at world’s best practice now and into future. Our local people have been working in regional communities for more than 30 years, to bring healthy, nutritious salmon to Australian dinner plates, through innovation and determination.The Conversation

Benjamin J. Richardson, Professor of Environmental Law, University of Tasmania

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

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Dinner to die for: how fish use their spines to fend off hungry seals


Vincent Antony, Author provided

David Hocking, Monash University; Felix Georg Marx, Te Papa Tongarewa; Silke Cleuren, Monash University, and William Parker, Monash University

What price are you willing to pay for food?

For most of us, that’s a question about money. But what if the cost were actual pain, injury and death? For some seals and dolphins, this a real risk when hunting.

We took a close look at a New Zealand (or long-nosed) fur seal that stranded at Cape Conran in southeastern Australia, and discovered it had numerous severe facial injuries. These wounds were all caused by fish spines, and they show the high price these animals are willing to pay in pursuit of a meal.



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Victim or perpetrator?

When the unfortunate seal was first spotted dead on the beach, it was clear something was amiss: the animal was emaciated, and had a large fish spine stuck in its cheek.

Location where the seal was found in south-eastern Australia.
David Hocking

A team of scientists from the Department of Environment, Land, Water and Planning (DELWP), Museums Victoria and Monash University decided to investigate, and took a CT scan of the seal’s head. The results were striking: fish spines had penetrated not just both cheeks, but also the nose and jaw muscles.

On closer examination, we also found ten stab wounds, likely from further fish spines that had been pulled out. The wounds were spread all over the face and throat, and at least some appear to have festered. They may have made feeding difficult, and ultimately may have caused the animal to starve.

These wounds were likely not the result of unprovoked attacks. They were probably inflicted by prey that simply did not want to be eaten.

3D computer models of the seal’s skull showing the position of the stingray barbs and ghostshark spines.
David Hocking

How to fight off a hungry seal … or at least teach it a lesson

Many fish species have evolved elaborate defence systems against predators, such as venomous spines that can inflict painful wounds.

Our seal appears to have been done in by two species of cartilaginous fish. One was the elusive Australian ghostshark (also known as elephant fish), a distant relative of true sharks that has a large serrated spine on its back.

The other was a stingaree: a type of small stingray with a venomous tail barb that can be whipped around like a scorpion’s tail. Its sting is normally aimed at would-be predators, but sometimes also catches the feet of unwary humans.

Deadly prey: the Australian ghostshark and stingaree, both armed with sharp venomous spines.
David Hocking
Sharp harpoon-like barb from the tail of a stingaree that was found embedded within the face of an unlucky New Zealand fur seal.
David Hocking, CC BY-SA

How to eat a spiky fish

Until recently, most of what we knew about the diet New Zealand fur seals was based on bony remains left in their poo. This technique largely overlooks cartilaginous fish, whose skeletons are made of cartilage instead of bone. As a result, we didn’t realise fur seals target these creatures.

New studies of the DNA of devoured prey in the seals’ scats now suggest they commonly feed on ghostsharks. Stingarees and other rays are less common, but evidently still form part of their diet. So how do the seals handle such dangerous prey on a regular basis?

It all comes down to table manners. Ghostsharks and rays are too large to be swallowed whole, and hence must be broken into smaller chunks first. Fur seals achieve this by violently shaking their prey at the water’s surface, largely because their flippers are no longer capable of grasping and tearing.

Fur seals can eat small fish whole, but need to tear large prey into edible chunks.

Shaking a fish in the right way (for example by gripping it at the soft belly) may allow seals to kill and consume it without getting impaled. Nevertheless, some risk remains, whether because of struggling prey, poor technique, or simply bad luck. The wounds on our seal’s cheeks suggest that it may accidentally have slapped itself with a ghostshark spine while trying to tear it apart.

Australian ghostshark being eaten by an Australian fur seal belly first, thus avoiding the sharp spine on its back.
Photo by Vincent Antony
Australian ghostshark being eaten by an Australian fur seal belly first, thus avoiding the sharp spine on its back.
Photo by Vincent Antony

Fish spines – a common problem?

One of the challenges we face as scientists is knowing how to interpret isolated observations. Are fish spines a common problem for fur seals, or was our individual just particularly unlucky? We don’t know.

New techniques like analysing DNA from scats means that we are only just beginning to get a better idea of the full range of prey marine mammals target. Likewise, medical imaging techniques such as CT scanning are rarely applied to marine mammal strandings, and injuries like the ones in our seal may often go unnoticed.

CT scans of the jaws of a wedgefish (Rhynchobatus sp.) from Dean et al. (2017)
Dean et al. (2017)

Nevertheless, fish spine injuries have been observed in other ocean predators, including dolphins, killer whales, and rays. One wedgefish described in another recent study had as many as 62 spines embedded in its jaw! Now that we know what to look for, we may finally get a better idea of how common such injuries really are.

For now, this extraordinary example vividly demonstrates the choices and dangers wild animals face as they try to make a living. For our seal, the seafood ultimately won, but we will never know if the fish that killed it got away, or if the wounds they left are evidence of the seal’s last meal.



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The Conversation

David Hocking, Postdoctoral fellow, Monash University; Felix Georg Marx, Curator Vertebrates, Te Papa Tongarewa; Silke Cleuren, PhD candidate, Monash University, and William Parker, PhD Candidate, Monash University

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