Why do sharks matter in the Great Barrier Reef?

Healthy coral reefs need sharks. In a coral reef ecosystem sharks are a top-level predator, sometimes called the apex predator. They are an important part of a reef’s ecosystem helping to maintain balance. A vulnerability assessment of sharks and rays on the Great Barrier Reef has determined some important facts about the role of sharks in the health of the GBR. There are currently 134 known species of sharks and rays.

Changing the balance of species in an ecosystem has a flow-on effect on other species in that ecosystem.

Hammerhead shark ©Mary Katherine Winn /dreamstime.com

Hammerhead shark
©Mary Katherine Winn /dreamstime.com

For example, if you remove sharks, the species those sharks would have eaten are likely to increase in number. The increased number of those species will likely have a greater impact on the species they eat, as there are now so many more ‘mouths’ to feed, and on it goes. Independently and in combination with other reef stressors, the health of entire reef ecosystems is significantly reduced.

Current threats to the Great Barrier Reef include:

  • commercial fishing
  • recreational fishing
  • coastal development
  • climate change and ocean warming and acidification, which result in coral bleaching
  • a new coal mine, which means new dredging and more shipping traffic (more coal mining also means the negative effects of climate change are likely to be worse.)
  • increased dredging and dumping at Abbott Point
  • extensive new dredging proposed in the port of Cairns to allow cruise liners to enter
  • nutrient-rich run-off from land-based activities
  • crown of thorns starfish
  • coral damage from cyclones and storms (it can take decades for a coral reef to recover from these).

Scientists are already warning of the deteriorating health of our incredible Great Barrier Reef. Adding yet another stressor to the coral systems may be more than they can take.

How much do you really know about sharks?

We often fear the things we don’t understand, and learning about the behaviour and habits of any potentially dangerous animal reduces your risk of harm.

Why do some people fear sharks? 

©CBPix / dreamstime.com

©CBPix / dreamstime.com

Are you afraid of sharks? Test yourself — what do you think of when you think of a shark? You probably don’t have the warm, fuzzy feelings you might when you think of a kitten or a puppy — sharks aren’t quite so cute to most of us. But, do you have the ‘Urgh!’ response? Do you think of rows of sharp teeth and fear being attacked by them? If so – why?

Maybe you have seen Jaws, the movie. This 1975 ‘thriller’ was a blockbuster in its day and has helped to shape the view many of us have of sharks. It was about a fictional person-gobbling great white shark with a taste for human flesh. Real sharks weren’t used in filming — instead mechanical monsters were used. Anyone who watched this horror film would understandably fear sharks as a result if they didn’t know much else about them.

How dangerous are sharks really?

Sure, sharks have killed people and given others horrible injuries. In Queensland, in the last 160 years (until 2013) there have been no fewer than 71 human deaths attributed to shark attack.  This figure averages to 0.4 deaths per year, or just under one human death every two years, due to shark attack. Every time a person is killed by a shark it is, of course, tragic. But, it is rare, especially when you compare it to other dangers.

How dangerous are our roads?

In 2013 there were 270 fatalities on Queensland’s roads.  So, do we worry we’ll be killed every time we get into our cars? If we were logical, we would be more worried about being harmed in a road accident than swimming in the sea. (Speaking of swimming, do you know how many people drown each year? In 2013, 64 people drowned in Queensland.  Hmmm … that’s more than 128 times the average number of people killed by sharks in Queensland each year.)

How dangerous are dogs?

Consider our ‘best friends’ for a moment. Around 13 000 people, including many young children, present at hospital emergency departments in Australia each year as a result of dog attacks. Yet we love our dogs.

So, if we were logical and rational, we’d have more swimming lessons, drive less, take more care with kids around dogs, and we wouldn’t be nearly so anxious about being attacked by sharks.

Do divers fear sharks?

Interestingly, many scuba divers who spend a lot of time close to sharks, unprotected by cages, don’t fear sharks. Have you ever wondered why they are able to swim safely with sharks? Don’t they have more reason than anyone to fear sharks?

If Shark Girl isn’t afraid of them, why are we?

Shark numbers are declining 

Maybe sharks should fear us. Humans kill unsustainable numbers of sharks each year. Estimates vary as much illegal fishing targets sharks and the ‘take’ is not recorded. But, we do know that the numbers are high and the practice is unsustainable. Sea Shepherd estimates the number at 73 million sharks per year.

Shark stocks are believed to be only 10% of their pre-industrial biomass, and this is declining. This isn’t surprising as they can take up to 20 years to reach sexual maturity and, unlike many other fish, don’t spawn large numbers of offspring.

Fishing for shark fin 

Black tip reef sharks © Ruthblack /dreamstime.com

Black tip reef sharks
© Ruthblack /dreamstime.com

The illegal trade in shark fins to supply the demand for shark fin soup is huge. Shark fins fetch a high price in Hong Kong, Taiwan, Singapore and China. Shark fin soup is a banquet food in ethnically Chinese cultures. With the high population and increasing affluence of the middle class in China, demand for shark fin soup is growing. Numerous boats have been caught fishing illegally in northern Australian waters to supply this profitable trade, which involves catching sharks and hacking their fins off, usually while they are still alive. The disabled sharks often are then released back into the water. Without fins they can’t swim so they sink to the bottom to die a slow death. Because the fins sell for so much more than the rest of the shark it is most profitable to keep just the fins. This trade is not only cruel — it is also wasteful.

Bycatch and flake

Bycatch of sharks is also contributing to their falling numbers. Bycatch is when species other than the target species is caught. Sometimes these species are kept and sold. Often they are killed regardless.

Shark is often sold in Australian fish and chip shops as flake. Eating flake helps to create a demand for shark products, which contributes to their demise.

Deliberate culling using nets and drum lines

Due to human fear of shark attack, many beaches in Queensland are ‘protected’ from sharks by nets and drumlines (baited hooks). Research has shown that shark nets and drum lines are not particularly effective, could potentially increase the risk of shark attack, and that there are better ways of managing shark and human interaction such as towing sharks out to sea. The impact of nets and drum lines on other species is also significant.

How does the future look for sharks? 

© Philcold / dreamstime.com

© Philcold / dreamstime.com

In a word: grim. Culling and overfishing, including illegal fishing, in combination with their slow maturation rate and low fecundity (sharks have few young) means that it is difficult for shark populations to recover from over-exploitation. As a result, sharks are in serious trouble and if the current rate of decimation of shark populations continues, many species of shark are on a path to extinction.

Why don’t we care more about this? Maybe many people just don’t realise what’s happening. Or, perhaps, is it because we have an irrational fear of sharks that we don’t see their demise as a problem? But, we should care. Healthy oceans need sharks and we need healthy oceans!

How you can help sharks

©Konstik / dreamstime.com

©Konstik / dreamstime.com

If sharks are to avoid extinction they need our help. There are many things you can do and ways you can get involved to help sharks to survive humans.

These films might inspire you …

Shark Girl