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The Guilt of One Shark: The History of the “Rogue Shark” Theory

Image Credit: Sharkcrew, CC BY-SA 4.0, Image Cropped

In February 2022, a British swimmer was killed by a great white shark (Carcharadon carcharias) near Sydney, Australia. Unsurprisingly, this gained significant media attention. State authorities launched a search for the culprit, with the aim of culling/relocating it away from people. This plan would seem, on the surface, to make perfect sense – shark ate human, make it go away. Yet this logic is largely based on a widespread misconception, and an outdated theory that science has long since abandoned.

Original Fin

If we go back a little further in the history of shark-human interactions, we come to July 1916. Over twelve summer days, the coast of New Jersey was the site of five incidents, four of them fatal. This story itself you may not know, but the film (and book) it is often widely cited as inspiring you certainly will: Jaws.

The evocative taglines and reused assets of the Jaws posters (Image Credit: Universal Pictures)

Less prominent in popular culture, but similarly inspired by this event, was the “rogue shark” theory. Popularised by Australian surgeon Dr Victor Coppleson between the 1930s and 1950s, it suggests “the guilt, not of many sharks, but of one shark”. It was built on the widespread concept of sharks as “man-eaters”, which dates at least as far back as the mid-1800s. Coppleson believed that the majority of sharks behaved “normally”, while “rogue” sharks were “vicious”, and “patrol a certain area…for long periods”. Such a shark, he further stated, “must be hunted until it is destroyed”.

You may note that this theory seems remarkably similar to the plot and characterisation of Jaws, painting a picture of a villain intent on the destruction of human life. But one is a classic of creature-feature cinema, and the other is supposed to be a serious scientific theory. And therein lies the – rather glaring – problem.

Innocent Until Proven Gillty 

Map showing the timeline and locations of the Jersey Shore attacks. 3 of the 5 attacks occurred in Matawan Creek (Image Credit: Kmusser, CC BY-SA 3.0)

In terms of evidence, perhaps the easiest place to start is with the events that inspired the whole idea. The five incidents occurred within twelve days, progressing northwards up the coast of New Jersey. A short time frame, and a (relatively) localised area. This led some scientists to conclude that this was likely the work of one individual, conducting a tour of violence up the coast. If a decent defence lawyer had been present, however, I suspect he would have called this evidence circumstantial at best.

A juvenile great white was also caught in the area around this time with human remains in its gut. So now there’s some hard evidence, supporting a perception of the crimes and the culprit. Except, perhaps not.

Three of the incidents occurred in brackish water – the domain, more typically, of the bull shark – and two in oceanic water. This could suggest at least two individual sharks, of separate species, were involved in the incidents. This, obviously, does not completely invalidate the theory, and remains a matter of some (rather futile, over a century later) debate.

Great White Lie

According to George Buress, of the International Shark Attack File (ISAF), there are only two or three cases in the past three centuries where it is thought likely that an individual shark has been responsible for multiple incidents. Only one of these is backed up by reasonable proof, and the ‘multiple’ attacks in this incident took place over 5 minutes, not the sort of days or weeks timeframe the rogue shark theory was associated with. This leads us to alternative, and in many cases more logical and better supported, theories as to why these incidents occur.

ISAF 2021 report poster (Image Credit: 2021 Report, ISAF)

Perhaps most obvious and self-explanatory, a considerable proportion of shark attacks (35% of confirmed shark-human interactions in 2021) are considered “provoked” by the ISAF. If someone starts prodding at a shark, no-one should be surprised if they get bitten. However, the simple unprovoked/provoked dichotomy widely used by the ISAF and elsewhere isn’t always particularly satisfactory. We do not understand enough about shark behaviour to draw a clear line under what counts as provocation. Would a shark perhaps view a person swimming too close, or above it, as a threat?

Numerous other theories have been proposed, and in 2014 John West, curator of the Australian Shark Attack File, summarised these in a single paper. He suggested that all the theories could generally fit into three broad categories; a) hunger, b) curiosity and c) aggression.

Most such theories are difficult to properly study and empirically assess, for obvious ethical reasons. However, much of the support for these theories comes from taking what we do know about shark behaviour and ecology, and the context of specific incidents, and drawing more informed conclusions from there.

For example, the majority of “unprovoked” incidents are classed by the ISAF as “hit-and-run” attacks. Many of these incidents occur in turbid, murky water, such as surf zones. In these conditions, it is easy to see how erratic splashing, shiny and reflective accessories, and contrasting colours could lead a shark to mistake a person for a more typical prey animal. These incidents also rarely involve repeat bites, with sharks typically moving on rapidly after finding the target not to their tastes.

We’re going to need a bigger theory…

In conclusion, understanding what leads to shark-human interactions, in order to better understand shark behaviour and reduce such incidents, requires proper investigation of the complex contextual factors surrounding such occurrences.

Scientific consensus, however, seems to be made up, at least regarding “rogue” sharks. Jaws was never intended to be a documentary, and we should stop treating it like one. The idea of the “rogue” shark, and language like it and “man-eater”, promote an unsubstantiated, malicious, criminalised perception of shark behaviour. This perception remains widespread, politicised and influential, despite simply not being backed up by the evidence.

The reality is that shark “attacks” remain incredibly rare, at an average of roughly 72 “unprovoked” incidents, and five fatalities, worldwide per year since 2016. For comparison, over one year between 2017 and 2018, 218 sharks were killed in culling and defence programs in Queensland, Australia, alone! While improvements have been made, sharks need us to change the way we view and discuss them, as our history together makes it abundantly clear that we are a far greater threat to the existence of sharks than they are to any single one of us.


Ben Bluck is a soon-to-be PhD student at the University of Southampton. He is broadly interested in almost everything to do with behavioural ecology and marine biology, especially sharks. You can find him being inactive on Twitter here (@anendemicshrub).

Avoiding Collisions With Trains By Fleeing… Onto The Tracks?

Image Credit: Clément Bardot, CC BY-SA 4.0, Image Cropped

Ungulates and trains – factors influencing flight responses and detectability (2022) Bhardwaj et al., Journal of Environmental Management, https://doi.org/10.1016/j.jenvman.2022.114992

The Crux

Trains are one of the most climate-friendly ways to cross long-distances. Whether it’s people heading off on holiday or transporting food, clothing or other goods, it’s a (usually) cheap and low-emissions method of travel.

Yet train-animal collisions can be a massive problem for wildlife. Deer in Europe, bears in North America, and elephants in India are three of the many, many groups of species that suffer mortalities every year when they’re hit by trains. The collisions aren’t exactly friendly to the trains either, with many drivers suffering from trauma and repairs often need to be made (granted, not as bad as being run over).

Understanding more about animal behaviour in the face of a train can help us figure out how to prevent these collisions. Today’s authors enlisted the help of Swedish train drivers in an attempt to understand how animals behave when confronted with an oncoming mass of metal.

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Searching For Standouts In The IPCC Reports

Image Credit: bertknot, CC BY-SA 2.0, Image Cropped

Let’s face it, IPCC reports are never a fun read. They’re a damming assessment of our ability to take care of the only planet we’ve got. Piecing through them to find the key takeaways is likewise a tough task, but since the final report (for this round) has now been submitted, I thought I’d reflect on what I’ve learned going through each step of the report over the last year.

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Can You Afford to be Picky?

The better, the choosier: A meta-analysis on interindividual variation of male mate choice (2022) Pollo et al. , Ecology Letters, https://doi.org/10.1111/ele.13981

Image credit: barloventomagico, CC BY-NC-ND 2.0

The Crux

Choosing who to reproduce with (mate choice – see Did You Know?) is a major player when it comes to the evolution of a species, yet it can be tough to know when individuals (and which individuals) should be choosy in their partners. A general trend is that when there are a plethora of potential mates available, too many for a given animal to mate with, they must make decisions on who to mate with. For many species, females tend to be the choosy sex, given the limited number of reproductive resources that are available to them (i.e., eggs) and how many males are usually available to mate.

Despite this commonality of female mate choice, male mate choice is also widespread in the animal kingdom. It is therefore important to know how different factors affect how a male chooses his mates. One factor that may play a key role is male quality, or the ability of a male to acquire mates. It could be that males that vary in their quality also vary in how picky they are. Today’s authors used a meta-analysis, or a “study of studies”, to understand how males make their decisions.

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Why A Big Brain Means A Longer Life (For Parrots)

Image Credit: Patrick Kavanagh, CC BY 2.0, Image Cropped

Coevolution of relative brain size and life expectancy in parrots (2022) Smeele et al., Proceedings of the Royal Society Biological Sciences, https://doi.org/10.1098/rspb.2021.2397

The Crux

Figuring out what exactly drives a species’ lifespan has proved more of a puzzle than it might at first seem. Sure, we can look at a single species and provide a few reasons for why it might live as long as it does, but finding predictable patterns relating different factors to life expectancy (let’s say longevity from here) is a little complex.

Take brain capacity for instance. There are three mostlymain theories (which are all somewhat linked) as to how brain capacity affects longevity. The cognitive buffer hypothesis suggests that the ability to solve puzzles granted by a larger brain enables a species to survive situations that other species couldn’t, giving them a longer lifespan. The expensive brain hypothesis suggests that a brain takes up more energy, therefore slowing growth and extending longevity. And the delayed benefits hypothesis suggests that a larger brain capacity allows for more skilled food-finding techniques, resulting in higher diet quality, less adult deaths, and most importantly, the ability for a longer learning period from their parents, resulting in more skill transfer.

Parrots are very smart creatures, almost on the same level as primates when it comes to relative brain size. Today’s authors wanted to test for links between brain capacity and longevity in parrots, and see if their findings lined up with any of the three hypotheses.

What They Did

The team drew their longevity data from Species 360, an organisation which collects information from conservation bodies worldwide. They used life expectancy as their measure of longevity, and compared it to relative brain size, as well as other features like body mass, latitudinal range and diet, which have been shown to affect longevity before.

The authors also tested a few other models which included measurements of developmental time and parental investment to see if either of these had an impact. Either being important could shed light on whether or not the expensive brain or delayed benefits hypothesis play a part in development.

Did you Know: Parrots As Invaders

Their bright colours and intelligence make parrots an inherently charismatic species, one we often sympathise with when we hear of their threatened status and degraded ecosystems. But some species of parrot are biting back, with rose-ringed parakeets (pictured below) now a damaging invasive species in much of Europe. A warming climate and rising numbers will likely only see their range expand.

Read More: Polly Want A City? Population Boom Sparks Call For Cull Of London’s Invasive Parakeets

What They Found

As suspected, larger parrot species tended to have longer lives. But larger relative brains also led to longer lives, though it wasn’t as large a contributor as body size was. The other parameters, including those related to diet, developmental time and parental investment, didn’t have a meaningful effect on parrot longevity in these models.

One added tidbit – the Cacatua, a genus which includes the sulphur-crested cockatoo (pictured above) were the longest lived birds, with the Large Fig Parrot of South East Asia coming in last, with a life expectancy of under two years.

Rose-ringed, or ring necked parakeets, which are causing a stir in European cities as their ivnasive populations expand (Image Credit: TheOtherKev, Pixabay licence)

Problems

Testing hypotheses in science is made easier by the fact that often they’re mutually exclusive, and concluding that research supports one hypothesis is often a direct result of rejecting another. Yet the researchers today were testing three hypotheses that were certainly not mutually exclusive, which really muddies the waters, and makes teasing the effects apart a little difficult.

So What?

The fact that diet and developmental factors had no effect here is interesting, as at least the delayed benefits hypothesis suggests that better diet may lead to longer lives. The expensive brain hypothesis also suggests that increased brain capacity contributes to a longer life by extending development time, so it’s odd that development time had no effect on longevity.

Ultimately the research here doesn’t disprove any of the theories, and perhaps shows most proof for the cognitive buffer hypothesis, suggesting that increased problem-solving abilities can contribute to longer lifespans. Since longer-lived species are often more likely to be threatened, their increased intelligence could be used as a conservation tool, seeing as we humans are often more enamoured with more intelligent species.


Dr. Sam Perrin is a freshwater ecologist who completed his PhD at the Norwegian University of Science and Technology who loves parrots almost enough to wish they would stop messing about and just invade Norway. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.

Let’s Get Meta… The Good Kind

Image Credit: Patrick Kavanagh, CC BY 2.0, Image Cropped

In my last post we talked about using images as data. This time we’ll consider another non-traditional source of data: the results of other investigations. Using results to generate more results? That seems weird… at first. But think about how science progresses. We build on other studies all of the time! Sometimes we use others’ findings as a jumping off point. Other times, studies invite us to see if we can reproduce their findings under new conditions or with respect to our own study site or species of interest.

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We’re In The Sixth Mass Extinction Event

Image Credit: Bernard Dupont, CC BY-SA 2.0, Image Cropped

The urgency behind the most recent IPCC report has thankfully garnered it a lot of attention worldwide*. It’s a report that was very frank in its desperation for people to take this threat as seriously as possible. Yet both this report and the one that hit us in February also made mention of one other key factor that has been swept under the rug – the ability of functioning ecosystems to both mediate and mitigate the impact of climate change.

Alongside a wealth of other benefits we gain from biodiversity, ecosystems play vital roles in helping us withstand the rigours of climate change. Wetlands and rivers protect us from increased flooding. Forests help mitigate extreme heat waves. Peatlands, mires, and permafrost are all crucial carbon sinks. Yet as species disappear, these ecosystems deteriorate, as pieces of the complicated web that they’re made up of disappear. It’s why the concept of mass extinction is so frightening.

But what is mass extinction? We often hear about the concept of a mass extinction, and the question of whether we’re currently in the sixth mass extinction is constantly thrown around. So let’s have a quick look at exactly what extinction itself means, what a mass extinction is, and why it’s increasingly obvious that we’re in one.

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