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Sharks of the Coral Sea

Scientists estimate that up to 90% of the big oceanic fish, including sharks, have been lost from our oceans over the past 50 years due to overfishing.  The Coral Sea is one of the world’s last ocean areas where healthy populations of large ocean predators still exist.  For this reason the Coral Sea is considered a global shark biodiversity hotspot and represents the opportunity to create a safe haven for sharks and other oceanic species.

Biological role of sharks

Sharks are ‘apex predators’ and play a vital role in the health of our ocean.  Removal of large predators from coral reef ecosystems throws out the natural balance. They are necessary to ensure the stability of the entire system. In both marine and terrestrial ecosystems, predator removal can cause a potentially irreversible cascade of complex knock-on effects (known as trophic cascades) that destabilise food-webs and the marine environment as a whole.  Due to the deeply interconnected food webs of our oceans, the full extent of potential and already occurring trophic cascades triggered by predator loss remains unknown, warranting further study amid growing concerns that cascades could be widespread.  We can spare the Coral Sea this fate.

Sharks in the Great Barrier Reef

A study conducted in the Great Barrier Reef (GBR) Marine Park reveals that shark populations are heavily affected by fishing but benefit greatly from the establishment of green zones (Marine National Park – closed to fishing). There is strong evidence that shark populations of the Great Barrier Reef are in decline due to fishing pressure, with Grey reef shark reduced to only 3% of natural populations on some fished reefs. Whitetip reef sharks had declined around 80% on fished reefs also. Small reserves or networks of reserves cannot offer sharks the same protection as a large scale marine reserve, due to the size of their home range.  The proposed scale of the Coral Sea Marine Reserve, its green zone and the removal of long-line fishing from two-thirds of the area will contribute greatly to the protection of shark populations.

Sharks in the Coral Sea

The proposed Coral Sea Commonwealth Marine Reserve encompasses almost 1 million km2.  Within the marine reserve is a series of zones which provide different levels of protection.  Importantly, key areas considered as significant habitat to the oceanic species that reside within it, including sharks, are currently left unprotected.  It would take only minor changes to improve this greatly.

Osprey Reef, for example, one of the world’s iconic shark diving experiences, has been given only a hairline of protection.  The green (marine national park) zone extends just 30-50m from the reef edge, leaving the entire reef slope and reef-associated shark population vulnerable. Grey, blacktip and whitetip reef sharks are regularly seen here, with silvertips, tigers and great hammerheads patrolling the blue. At least ten species of pelagic sharks move through the Coral Sea including shortfin mako, bronze whalers, oceanic whitetips, hammerheads, tiger, and great white sharks. The Coral Sea is also home to a rare whale shark aggregation and 52 species of deepwater sharks and rays, 18 of which are unique to the area.

Our Ask

As the process for the effective establishment and management of the proposed Coral Sea Marine Reserve continues, we will now ask the Environment Minister Tony Burke to develop a comprehensive and effective management plan.

We will urge him to extend the marine national park zone around Shark, Vema and Osprey Reefs further west by 10kms to ensure that the important reef-associated pelagic species and reef slopes are fully protected as they are vital elements of the reef ecosystem.

In the southern Coral Sea, where the shark biodiversity hotpot is located, longline operators have indicated they are willing to exit the area down to 22degrees south, with fair financial compensation. We will then urge Burke to increase the protection of this area and effectively protect the seamounts, Townsville Trough (an important migratory pathway) and part of the shark biodiversity hotspot that has currently been left vulnerable.

Help us to make the Coral Sea a safe haven for sharks:  The Ocean takes care of us, let’s return the favour!

Permanent link to this article: http://cafnec.org.au/2012/11/12/sharks-of-the-coral-sea/