FactFile: the facts on shark bites and shark numbers



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The CSIRO has provided new estimates of population sizes for White Sharks in Australian waters.
Fiona Ayerst/Shutterstock

Jane Williamson, Macquarie University and Vincent Raoult, University of Newcastle

Are there more sharks in Australian waters than there used to be, and are interactions between humans and shark increasing? Some Australian politicians have claimed that to be the case.

Let’s look at the research.

The most reputable source for shark incident data in Australia is the Australian Shark Attack file, which is collated at Sydney’s Taronga Zoo.

The map below, created by The Conversation using data from the Australian Shark Attack File, shows incidents between sharks and humans in Australia between 1997 and 2017.

You can use the filter buttons in the map to explore the data by year, season, the type of injury, the type of shark involved, the type of incident – or a combination of all the filters. Press the ‘show all’ button to reset the search.

https://cdn.theconversation.com/infographics/243/f87e27e72eb6545d5422e204b9894dedaad0f92f/site/index.html

The number of recorded encounters between sharks and humans in Australia increased modestly between 1997 and 2017, but the reason for this is unclear. Over those two decades, the Australian population increased by 33%, but that alone doesn’t explain the increase in recorded shark encounters.

Correcting for the growth in human population in Australia, the data show that between 1997 and 2017:

  • incidents resulting in injury increased by 1.59%
  • incidents without injury increased by 0.36%, and
  • fatalities increased by 0.07%.

Encounters between humans and sharks are extremely variable over time, and difficult to predict. The increases in recorded incidents between 1997 and 2017 are relatively small, and may be explained by factors not related to shark populations – such as increases in the reporting of shark encounters, or increasing beach use.

https://cdn.theconversation.com/infographics/159/62c30e6dedecffbbeb4e059c8ab0e573d756f61b/site/index.html

Are there more sharks off the Australian coast?

White Sharks (formerly Great White Sharks) are recorded as being responsible for 28 of the 36 fatal shark encounters in Australian waters between 1997 and 2017, and are the primary target of shark mitigation strategies of the Western Australian, New South Wales and Queensland governments.

So, has there been an increase in the number of White Sharks in Australian waters?

Estimating population numbers in the marine environment is difficult, especially for long-lived migratory species like White Sharks.

However, there is no evidence that White Sharks numbers are on the rise, either in Western Australia or along the Eastern coast. Despite targeted conservation efforts, the available research show stable or slightly declining numbers in these populations.

There are two distinct populations of White Sharks off Australian coasts – one to the west, and another to the east of Bass Strait, which separates Tasmania from mainland Australia. The eastern population includes New Zealand White Sharks.

Recent work by the CSIRO through the National Environmental Science Program’s Marine Biodiversity Hub using innovative DNA analysis has provided us with the most detailed and reliable estimates of population size we have for this species.

The CSIRO study shows there has been a slight decline in adult White Shark populations since the year 2000.

Current adult abundance for the eastern Australasian population is estimated at 750, with an uncertainty range of 470 to 1,030. The southern-western adult population is roughly double the size, estimated at 1,460, with an uncertainty range of 760 to 2,250.

Including the available information about juvenile White Sharks, estimates of total size for the eastern population in 2017 was 5,460, with an uncertainty range of 2,909 to 12,802.

It’s difficult to detect population trends with White Sharks because of the length of time it takes juveniles to reach maturity – around 15 years. As protection of White Sharks began in the late 1990s, any changes in abundance would only be starting to appear in current populations.

How else can we measure White Shark populations?

The traditional way of measuring shark and fish populations is by examining catches in commercial fisheries over long time periods. By correcting for the level of fishing effort – which is done by looking at things like the number of nets, hooks and tows deployed by fishermen – scientists can assume that changes in the “catchability” of sharks is related to their abundance.

But due to the relative rarity of catches of White Sharks by fishing vessels, this approach is less reliable for this species than the more recent genetic studies conducted by the CSIRO and outlined above.

Western Australia has a detailed measure of White Shark numbers assessed by catch data. A report published by the Western Australian Department of Fisheries in 2016 attempted to model changes in the southern-western Australian White Shark population since the late 1930s. The authors outlined four different plausible scenarios, none of which suggested a continuous increase in the number of White Sharks.

In New South Wales, there has been a cluster of shark bites in recent years. Data from the NSW Shark Meshing (Bather Protection) Program, managed by the NSW Department of Primary Industries, show a recent increase in White Sharks caught in nets placed near ocean beaches.

But when it comes to thinking about shark populations, we should not assume that these two facts are related. It’s important to remember that just because two things may correlate, it doesn’t mean that one caused the other.

These patterns could mean that the animals are coming closer to shore, rather than a population increase (or decrease).


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Shark and human interactions: what factors are at play?

A 2016 paper examined six global shark bite “hotspots” – the United States, South Africa, Australia, Brazil, Reunion Island and the Bahamas – and concluded that when it comes to encounters between sharks and humans, there are a range of causes at play.

These include:

  • rises in human population
  • habitat destruction/modification
  • changes in water quality
  • climate change
  • changing weather patterns, and
  • the distribution/abundance of prey.

The authors also noted that shark encounters appear to happen in clusters. For example, 2009 saw a spike in shark encounters off the New South Wales coast. This coincided with an increase in beach attendance and beach rescues during what was an unusually warm summer for south-east Australia.

A 2011 paper highlighted the popularity of water sports as a factor contributing to increased human-shark encounters. More people are taking part in water sports, and improvements in wetsuit technology mean that people are in the water for longer throughout the year.

However, there is limited information on the number of people who use Australian beaches, so this explanation needs to be further studied.

The ConversationIt’s vital that any strategies put in place to reduce the number of unprovoked encounters between humans and sharks in Australian waters are carefully considered, and based on the best available research.

Jane Williamson, Associate Professor in Marine Ecology, Macquarie University and Vincent Raoult, Postdoctoral fellow, University of Newcastle

This article was originally published on The Conversation. Read the original article.

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Dingoes do bark: why most dingo facts you think you know are wrong


Eloïse Déaux, Université de Neuchâtel

As I visited a wildlife park in New South Wales in 2011, the keeper at the daily “dingo talk” confidently told us that “pure dingoes don’t bark”. After five years studying dingoes’ vocal behaviours, I can tell you that this is a myth. Dingoes do bark!

While travelling around Australia to study dingoes, I have had the opportunity to meet and talk with all sorts of people. One thing I realised is that the “dingoes don’t bark” belief is widespread – and it isn’t the only unproven dingo myth out there.

Lots of people in Australia take these three myths as hard facts:

  1. “pure” dingoes don’t bark

  2. “pure” dingoes are all ginger

  3. dingoes are “just dogs”.

But none of these are actually true and here’s why.

Myth 1: dingoes don’t bark

Anyone who has been around dingoes for long enough will tell you that they do bark, but not like domestic dogs. Dingoes’ barks are generally harsher, and given in short bursts.

Domestic dogs will bark anytime, anywhere, for anything (often to their owners’ or neighbours’ chagrin). This is not the case with dingoes. They will generally bark only when alarmed – such as when researchers trap them to fit a radio tracking collar, or if you stumble across one in the bush.

Dingo barking sequence.
Eloïse Déaux, CC BY-NC-ND133 KB (download)

Dingoes can also bark if they get very excited (about food, for example) but this is quite uncommon. The rarity of these events probably explains the prevalence of the “no barking” myth – wild dingo barking just doesn’t happen often enough for most people to witness it.

Another associated misconception is that captive dingoes will learn to bark from listening to domestic dogs. Although humans are very good at learning new sounds – indeed, that’s how we acquire our language – most other species (including canines) can make only a limited range of vocal sounds, and can’t learn new ones.

So the fact that captive dingoes bark actually confirms that they have barking abilities right from the start. It is, however, possible that by listening to nearby domestic dogs, captive dingoes learn to bark more often and in more situations than they otherwise might.

It is easy to see how this myth might harm efforts to protect dingoes. Imagine a well-meaning pastoralist shooting or baiting anything that barks, in the mistaken belief that it’s not a dingo.

Myth 2: all pure dingoes are ginger

The “typical” dingo that people picture in their minds – think Fraser Island – will be ginger (or tan) with white feet and a white-tipped tail. But dingoes, like people, come in a variety of shapes and colours.

Importantly, although ginger dingoes make up about three-quarters of the population, there is genetic evidence that their coats can also be black, black and tan, black and white, or plain white.

A black and tan dingo…
Tim Pearson
…and a white one.
Tim Pearson

There is also a lot of variation in the size and shape of white patches and these may even be absent altogether. It’s often thought that dingoes that lack ginger fur or white patches are dingo-dog hybrids, but this is not necessarily true.

Like the no-barking myth, misconceptions about coat colour can potentially harm dingo conservation. If we were to protect only ginger dingoes, we would unwittingly reduce the natural genetic variation of the population, making it more vulnerable to extinction.

Myth 3: dingoes are just dogs

This is perhaps the hardest belief to address, because it can vary depending on whether we look at their behaviours, ecology or origins. But this concept is arguably even more relevant to their conservation and management.

So is a dingo a dog? Although dogs’ evolutionary origins are still unclear, we know that dingoes are descendants of animals domesticated long ago somewhere in Asia and then brought to Australia. Dingoes are thus an ancient dog breed and so, yes, dingoes are dogs.

However, we also know that dingoes arrived in mainland Australia roughly 5,000 years ago and have since been isolated from all other canines right up until European settlement. Some experts argue that this makes them distinct enough to warrant protection from hybridisation with domestic dogs.

As dingo researcher Ben Allen puts it, “pure ones need to be distinguished from hybrid ones somehow, and it is the pure ones that have conservation value as a species”.

But as fellow dingo expert Guy Ballard points out, dingoes are undeniably a type of dog, so arguably all that really matters is that their function as top predators in the ecosystem is preserved.

But there’s a catch (as Ballard has acknowledged): we do not know whether dingoes, feral dogs and hybrids behave similarly – or in other words, whether all three can perform the same ecological role.

We do know that India’s free-ranging dogs behave very differently from Australian dingoes: they are inefficient predators, do not form packs and do not breed cooperatively. This suggests that, in terms of their behaviours, dingoes may be very different from other types of dogs after all.

Until we know more, the best approach to safeguarding dingoes and their role in the ecosystems might be to view and treat them as completely separate and distinct from other free-ranging dogs in Australia.

Far from being “just dogs”, dingoes really are unique dogs.

The Conversation

Eloïse Déaux, Postdoctoral fellow in mammal vocal communication, Université de Neuchâtel

This article was originally published on The Conversation. Read the original article.