Let’s argue against the Shark Cull with science

There’s been a lot in the news recently about the implementation of the Shark Cull (or, as the Government put it, the “shark protection measures”) here in Western Australia.  Just as I am not a climate scientist, I am not a shark biologist, and cannot claim to be a shark expert.  However, as a marine ecologist who focuses on ecosystem scale research, I feel that I can give a relatively informed opinion!  Unsurprisingly, I am against the cull, but my arguments against it don’t completely align with those of the anti-cull protestors.

There is clearly a lot of emotion in this debate, from those for and against the cull.  This isn’t really surprising given the fact that there have been seven shark-related fatalities in Western Australia over the last 3 years.  This emotion has spilled into the argument around shark culling, and this is where I see a big problem.  The debate is being framed as an ethics debate, with external, undecided observers most likely seeing the debate as a “Shark rights vs. human rights” issue.  And guess what.  This plays right into the hands of the pro-cull side.  Although I definitely agree that animal ethics are important, human rights will always win in the battle for public hearts and minds (which ultimately, influences policy).  This emotive debate will always be won by the pro-cull side, who can conjure horrific images of people being eaten by a shark, ala Jaws.  Indeed, just this week a pro-cull commentator was arguing for the killing of sharks by raising the scenario of a child potentially being taken by a shark at a Perth beach (prizes for which logical fallacy that is!). I’m sorry, but there is no point in arguing against the shark cull based on shark rights when this is the type of argument that you face!  However, we have an ace up our sleeve on the anti-cull side; we are backed up by scientific data and logic, and scientific research can provide us with compelling evidence against the cull!  So I think we should primarily use rational arguments against the shark cull.  Plenty of actual shark experts (as well as renowned ecologist and the Eureka Prize winner, Euan Ritchie) have stated far more eloquently the detailed science against this cull, and potential alternatives, but here’s my attempt at a run down.

We’ve known for a very long time that when apex predators are removed from natural ecosystems, bad things start to happen.  We call this type of process trophic cascade, or more specifically in this case, top-down control.  The removal of the top predator allows it’s direct prey  to expand in number, and this expansion can be rapid when predation is the main controller of the prey population.  The expansion of these populations then leads increased predation or herbivory, and can potentially lead to a decimation in plants and animals lower in the food chain.  So, even though we only removed that top species (the apex predator), it had consequences for the whole food web, and can result in a distinct shift in the type of ecosystem we see.  This isn’t just a problem for the environment, these changes can lead to social and economic issues in certain circumstances.

About the most famous example of the severe impacts caused by the removal of apex predators comes from the complete destruction of the grey wolf population in Yellowstone.  Wolf populations were under severe threat in the area, and the introduction of a government-led predator control programmes (sound familiar???) led to the complete extinction of wolves in Yellowstone Park in the mid 1920s.  Over the subsequent decades, environmental conditions at Yellowstone declined severely.  This was driven by a rise in elk numbers, allowed to proliferate due to the removal of their main cause of mortality (being eaten by wolves!).  The increase in elk numbers led to huge overgrazing, in turn decimating plant populations, which led to impacts on other animals at Yellowstone.  The removal of the grey wolf caused this trophic cascade, threatening one of America’s most famous national parks at an environmental, cultural, and economic level.  The re-introduction of grey wolves into Yellowstone in the 1990s resulted in direct reduction in elk numbers to more sustainable levels, resulting in the recovery of many plant species, and also restructured populations of other animals in the ecosystem (showing the diverse and varied ecological connections and feedbacks).  In short, when we mess with the top predators, lots can go wrong, and this recipe for disaster is made worse when we factor in climate-driven changes to our environment!

The evidence for these trophic cascades after apex predator removal is widespread across lots of different ecosystems, including in the ocean, with sharks often present as apex predators.  Even in relatively pristine ecosystems with low levels of human impacts, it is clear that sharks can play a hugely important role in structuring the ecosystem.  Up in Shark Bay where I conduct most of my research, tiger sharks are the apex predator (and incidentally, are on the list of shark species to be culled as part of the policy).  The presence of large tiger sharks influences the feeding preferences of many of the herbivores like turtles and dugongs in Shark Bay, which in turn results in changes to spatial patterns of herbivory pressure on seagrass meadows (which impacts many other organisms – complex feedbacks in action!). Clearly, large sharks play a hugely important role in our ocean, and if we lose them, it will have knock on effects, that could extend to economic consequences such as negative impacts on fisheries – commercial and recreational.

So the science warns against instigating the cull, and previous attempts at using shark culls to prevent attacks on humans have not worked.  There is also no evidence of a significant increase in shark numbers or shark attacks (despite the 7 fatalities in 3 years).  It may sound like blame can be focussed solely on the state government for implementing the policies in spite of this, but the media has also played a role.  The ferocity and intensity of the language used in the West Australian media when describing sharks has left a lot to be desired, often perpetuating the fear mentality driven by films like Jaws.  Yes, shark attacks are tragedies, and tap into a primal fear that has evolved with us (the fear of being eaten!).  However, this does not justify stirring up this fear to critical levels by falsely describing sharks as ‘rogues’ and talking of ‘feeding frenzies’.  Much like in the climate debate, objective journalism seems to be missing from the shark debate.

Justified or not, there is fear within some sections of the public against sharks, which prompted the cull in the first place.  This fear does not justify the cull – imagine a world where we based all policy on emotion instead of reason!  If politicians do feel the need to be seen to be doing something about the attacks, there are plenty of other alternatives (some like tagging and increasing research funding are already being done) that are backed up by science.  Even under the current drum line policy, sharks could be towed out to sea, tagged and released away from our busy beaches, as done successfully in Brazil.

The debate over the cull has become polarising. Anti-cull protestors (with the best of intentions), have entered into a damaging debate with the pro-cull side following a narrative of ‘shark rights vs. human rights’, with the science taking largely a back seat.  Instead, let’s emphasize the science, and tell people what we all stand to lose by implementing policies such as this.  Let’s explain to people how their favourite swimming spot might change dramatically if we get rid of large sharks.  Let’s describe why catching fish might become even more difficult with large sharks gone.

And let’s not be afraid of leaving a little bit of risk and wilderness associated with our amazing natural playgrounds!


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