Wednesday, April 9, 2014

When animals attack: are shark nets based on good science?

An endangered grey nurse shark. Up close, they look like less Jaws and more Gary Larson's Far Side.

Here’s a little insight. I am scared of sharks. Not just in the ocean. If I am flicking through a book and a turn the page over and see a shark, I recoil. Fortunately, during my day to day activities (working at my desk, working in a clinic, all on land) I rarely (i.e. never) encounter them and I don’t even give them a chance since I have a policy of avoiding ocean swimming.

I watched Jaws at an impressionable age. So terrified was I of the vision of a shark rushing out at me from below the water that I refrained from taking a bath for some years after. This is no minor deal – anyone who knows me knows that I practically live in the bath. But for a while there (and I was a child) I convinced myself that the plug was a black shark eye, and just couldn’t go there.

Yet more people are killed driving to or from the beach, or by drowning, than by shark attack. I don’t avoid cars or motor vehicles and I will (now) happily jump in a body of water like a bath or even a swimming pool. According to the stats, I am modifying my behaviour to avoid the thing that is least likely to kill me.

This chart was present at the talk last night. (NB I don't have an official source for this, so please don't take these figures on face value - peer reviewed data is always more reliable. But what this DOES illustrate is the relative risk. If you want to know more about how Aussie's died last year, see the Australian Bureau of Statistics).
I share this insight because it illustrates that our response to fear can be irrational. In my case the response wasn’t harmful (thank goodness for showers – and lucky Sharknado wasn’t released until I was an adult), but it can be.

When someone is bitten by a shark in Australia, fatally, the response – historically – has been to go and kill the perpetrator. There’s an element of vengeance as well as a sense that the shark hunters are protecting us from this rogue menace.

In Australia, the use of shark nets and drum lines to prevent sharks from munching swimmers, divers and fisher-people has been the subject of very emotive debate, particularly in Western Australia where Government policy around shark culling has come under enormous criticism.

Whether you are marine-oriented or not, it’s a brilliant example of the way we react when human-animal interactions go badly – for us (I don't know any Homo sapiens with a paralysing fear of spear-fisherpersons).

Last night the Sea Life Conservation Fund hosted a panel discussion about sharks, shark nets, risk and risk perception and it was fascinating. I admit to being one of those naïve individuals who assumed that a netted beach was something protected by a net barrier that extended headland to headland, 24/7, keeping sharks on the other side.

How wrong I was. From the DPI’s Dr Bob Creese, we learned that the nets, on 51 beaches in NSW, are around 6 metres high in 12 metres of water – extending for around 150 metres each. They are positioned around 500m offshore. The rationale is that most sharks will swim at about this level at this depth – and so other fish can swim over, and bottom-dwellers and rays can go under. So they do NOT prevent shark access to swimming beaches! Sharks, if they want to, can swim right over the top. Of course they don’t always and the nets do catch sharks. Moreover the nets are in place at least 14 days per month – not every day. 

They also catch what is euphemistically known as “by-catch”, a word with similar connotations to “collateral damage” used by some Governments to describe the death of civilians during military operations. By-catch refers to your non-man-eating sharks, dolphins, whales, dugongs, turtles etc. that become caught in nets. Under the NSW Shark Meshing (Bather Protection) Program the nets must be checked regularly for by-catch – every 72-96 hours. But that means an animal can struggle for up to 96 hours – long enough to hang itself in an entangled net.

Shark nets are killers of sharks, but they are indiscriminate killers – and endangered species, including the grey nurse shark of which there are only an estimated 1200 in the wild, get trapped and die.

Shark bite survivor Lisa Mondy couldn’t be present last night, but she wrote a letter describing her experience of being attacked while swimming back toward her wakeboard at Jimmy’sbeach on a crystal clear day. The response from the media, she said, was almost as scary as the attack.

She was and remains traumatised by that event in 2011, but was concerned that the response to a shark attack often consists of “punishing a species for a random, probably mistaken, act of nature” and urged people to analyse events scientifically, rather than maintain unfocused vengeance. She also cited a figure that I found interesting and somewhat alarming - 40% of sharks are caught on the beach side of nets! 

Dr Chris Neff supported that point, and provided background for the dominating rogue shark theory, and the history of nets in Australia. He suggested that when we analyse shark fatalities in the 30s, 40s, 50s and 60s – many “fatal” attacks were survivable by today’s standards – we just didn’t have the antibiotics, blood transfusions, high-tech ICU gear and reliable transport to hospital. Many victims died within the days or week after an attack rather than in the water. 

Professor David Booth took an ecological lens to the problem. In ecosystems the big sharks are what we call “apex predators”, and they play a role in keeping the mesopredators in check. Remove the apex predators and the meso predators over-populate and eat everything in sight, changing the whole ecosystem.

According to this paper, "Mesopredator outbreaks often lead to declining prey populations, sometimes destabilising communities and driving local extinctions." 

The biggest threat to the world’s sharks is overfishing, and there’s plenty of that, but Booth reminded us that we remove sharks from their ecosystems to our own detriment – we’re robbing ourselves of potential food sources too.

Alexia Wellbelove, from Humane Society International, revealed that from 1930 to April 2013, shark nets had had a huge impact on the marine ecosystem, trapping 15506 non-target species, catching more “by-catch” than sharks.

In other words, there is no definitive data that shark nets protect us – but concrete data that they are detrimental to wildlife.

So why keep on with the nets? They build confidence (even if it’s false). As a friend of mine brilliantly wrote:

This is the basis of the famous dread factor that Paul Slovic described in his classic works on risk perception. It doesn't matter how low the real risk or likelihood of harm is, what matters is what you think the likelihood is.  And there are so many differences between what is technically and what is emotionally the likelihood.  Unexpected harm arises from the actions people take to protect themselves from the perceived but improbable harm.  With sharks, the netting probably does a lot of harm for little benefit.  However, since the nets went in no shark (I repeat not one single shark) has been seen in my street - so I am definitely not in favour of removing those nets. 
Its someone puzzling in Australia that when a shark bite incident occurs, the Government feels compelled to do something.

Dr Neff, with the support of the Sea Life Conservation Fund, Sydney Sea Life Aquarium and the University of Sydney, surveyed 674 people at Sydney Aquarium (42 per cent were born in Australia, 58 per cent born outside of Australia) and has shared some new results with SAT.

After the talk I walked out of the venue and ran into this giant model of a great white shark. Despite the fact that this is an inanimate object, that I was on land, and in an environment where models of sea life abounded, I gasped audibly.
He was particularly looking to see if viewing sharks in the aquarium changed people’s perceptions and it did.

Most (77%) either didn’t feel frightened of sharks, or felt moderately frightened (23% were still extremely frightened). But seeing the sharks helped. I can attest to that. Once you look at these sharks, they aren’t nearly as scary (I went as far as diving with them at Manly Aquarium, which was adrenalin-fuelled but turned out to be a not-at-all scary experience).

My visit to Manly Aquarium to confront some of my Jaws issues (as opposed to issues with my jaws).
Interestingly, when asked who was to blame when sharks bite, only 2-4% blamed the Government; 6-8% blamed the shark; 9-11% weren’t sure, 33-40% said no one and 38-44% blamed the swimmer. Makes sense. If we go into the water, as land mammals, we have to assume some risk, don’t we? 

Increased levels of fear were not associated with increased levels of blame.
Policymakers often react to shark bite incidents because they are concerned they will be blamed. But the above results suggest that this might be an unfounded fear (though it would be interesting to survey non-aquarium goers, as I suspect some of the most diligent shark-o-phobes (selachophobes) would avoid the aquarium like the plague).

But certainly those surveyed had differing views about how Governments should respond to shark bites.

Around 4% thought shark hunts were a valid response, 9% would provide more shark nets, 18% would leave the shark alone and 69% felt compelled to educate the public. Around 87% of those surveyed preferred Government responses that did not kill sharks. But it is interesting that 13% of aquarium visitors did – so the surveyed population, as Dr Neff pointed out, aren’t “shark-huggers”. 

Am I a shark hugger? Well, to some extent last night yes.

Confession: I hugged this shark. 
Someone was dressed in a shark suit and I hugged them. I've not lost my sometimes irrational fear of sharks. But I do have rational concerns about fear and know that the gap between percieved risk and actual risk can be enormous. If we're making life and death decisions based on risk assessments - and this should apply to any species - we need to base them on good science, not hysteria. If we don't, we risk doing much more harm than good.