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.

Aren’t we in a drought? The Australian black coal industry uses enough water for over 5 million people


Ian Overton, University of Adelaide

Water is a highly contested resource in this long, oppressive drought, and the coal industry is one of Australia’s biggest water users.

Research released today, funded by the Australian Conservation Foundation, has identified how much water coal mining and coal-fired power stations actually use in New South Wales and Queensland. The answer? About 383 billion litres of fresh water every year.

That’s the same amount 5.2 million people, or more than the entire population of Greater Sydney, uses in the same period. And it’s about 120 times the water used by wind and solar to generate the same amount of electricity.




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Monitoring how much water is used by industry is vital for sustainable water management. But a lack of transparency about how much water Australia’s coal industry uses makes this very difficult.

Adani’s controversial Carmichael mine in central Queensland was granted a water licence that allows the company to take as much groundwater as it wants, despite fears it will damage aquifers and groundwater-dependent rivers.

Now more than ever, we must make sure water use by coal mines and power stations are better monitored and managed.

Data on total water use by coal mines is not publicly available.
Shutterstock

Why does coal need so much water?

Mines in NSW and Queensland account for 96% of Australia’s black coal production.

Almost all water used in coal mines is consumed and cannot be reused. Water is used for coal processing, handling and preparation, dust suppression, on-site facilities, irrigation, vehicle washing and more.

Coal mining’s water use rate equates to a total consumption of almost 225 billion litres a year in NSW and Queensland, which can be extrapolated to 234 billion litres for Australia, for black coal without considering brown coal.

About 80% of this water is freshwater from rainfall and runoff, extracted from rivers and water bodies, groundwater inflows or transferred from other mines. Mines are located in regions such as the Darling Downs, the Hunter River and the Namoi River in the Murray-Darling Basin.




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The other 20% comes from water already contained in tailings (mine residue), recycled water or seepage from the mines.

The burning of coal to generate energy is also a large water user. Water use in coal-fired power stations is even harder to quantify, with a report from 2009 providing the only available data.

Water is used for cooling with power stations using either a once-through flow or recirculating water system.

The water consumed becomes toxic wastewater stored in ash ponds or is evaporated during cooling processes. Water withdrawn is returned to rivers which can damage aquatic life due to the increased temperature.

No transparency

Data on total water use by coal mines is not publicly available. Despite the development of Australian and international water accounting frameworks, there is no reporting to these standards in coal mine reports.

This lack of consistent and available data means water use by the coal industry, and its negative effects, is not widely reported or understood. The problem is compounded by complex regulatory frameworks that allow gaps in water-use reporting.

A patchwork of government agencies in each state regulate water licences, quality and discharge, coal mine planning, annual reviews of mine operations and water and environmental impacts. This means that problems can fall through the gaps.

Digging for data

An analysis of annual reviews from 39 coal mines in NSW, provided data on water licences and details of water used in different parts of the mine.

Although they are part of mandatory reporting, the method of reporting water use is not standardised. The reviews are required to report against surface water and groundwater licences, but aren’t required to show a comprehensive water balanced account. Annual reviews for Queensland coal mines were not available.

Collated water use — both water consumption and water withdrawal – showed coal mining consumes approximately 653 litres for each tonne of coal produced.

This rate is 2.5 times more than a previous water-use rate of 250 litres per tonne, from research in 2010.

Using this rate the total water consumed by coal mining is 40% more than the total amount of water reported for all types of mining in NSW and Queensland by the Australian Bureau of Statistics in the same year.

By the numbers

NSW and Queensland coal-fired power stations annually consume 158,300 megalitres of water. One megalitre is equivalent to one million litres.

A typical 1,000-megawatt coal-fired power station uses enough water in one year to meet the basic water needs of nearly 700,000 people. NSW and Queensland have 18,000 megawatts of capacity.

Coal-fired generation uses significantly more water than other types of energy.

In total, coal mining and coal-fired power stations in NSW and Queensland consume 383 billion litres of freshwater a year – about 4.3% of all freshwater available in those states.

The value of this water is between A$770 million and A$2.49 billion (using a range of low to high security water licence costs).

They withdraw 2,353 billion litres of freshwater per year.


Author provided/The Conversation, CC BY-ND

The problem with large water use

Coal mining is concentrated in a few regions, such as the Hunter Valley and the Bowen Basin, which are also important for farming and agriculture.

In NSW and Queensland, the coal industry withdraws about 30% as much water as is withdrawn for agriculture, and this is concentrated in the few regions.

Coal mining and power stations use water through licenses to access surface water and groundwater, and from unlicensed capturing of rainfall and runoff.

This can reduce stream flow and groundwater levels, which can threaten ecosystem habitats if not managed in context of other water users. Cumulative effects of multiple mines in one region can increase the risk to other water users.

The need for an holistic approach

A lack of available data remains a significant challenge to understanding the true impact of coal mining and coal-fired power on Australia’s water resources.

To improve transparency and increase trust in the coal industry, accounting for water consumed, withdrawn and impacted by coal mining should be standardised to report on full water account balances.




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The coal industry should also be subject to mandatory monthly reporting and a single, open-access point of water data must be created. Comprehensive water modelling must be updated yearly and audited.

Coal water use must be managed in a holistic manner with the elevation of water accounting to a single government agency or common database.

Australia has a scarce water supply, and our environment and economy depend on the sustainable and equitable sharing of this resource.The Conversation

Ian Overton, Adjunct Associate Professor, Centre for Global Food and Resources, University of Adelaide

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