A Marine Protected Area (MPA) was established in 2010 around the Chagos Archipelago, a collection of tiny atolls in the Indian Ocean owned by the UK as the British India Ocean Territory (BIOT).
The MPA bans all fishing inside the 640,000 sq km zone, but illegal fishing – mostly of sharks – is known to have continued as enforcing the enormous conservation area is limited to a single aging vessel.
New research by a team led by the University of Exeter and the Zoological Society London has concluded the estimates of illegal shark fishing are significantly undercounting the reality.
Enforcement data suggests about 14,000 sharks were caught in the Chagos MPA from 2010 to 2020. But after consulting local fishermen in the region, the researchers believe many vessels were able to fish in the region undetected.
This provides "clear evidence that total extraction was considerably higher" than the estimate of 14,340 based on detected vessels, a new paper warns.
"Enforcement of MPA rules in a large, remote area such as this is extremely difficult," said the study’s lead author Claire Collins, of the University of Exeter.
"Our findings highlight the threat of illegal fishing to sharks in the BIOT MPA, which is home to critically endangered species such as the oceanic whitetip and scalloped hammerhead.
"Fishers often target reef areas, where many of the sharks are juveniles, and taking sharks at this life stage could be especially damaging to species numbers.”
Despite the prevalence of illegal shark fishing, the MPA continues to act as a vital refuge in the Indian Ocean and shark numbers remain higher inside it than elsewhere, she added.
As part of the study, researchers carried out interviews and focus groups with two Sri Lankan fishing communities often associated with illegal fishing in the MPA.
Locals told the scientists they knew of many boats which came and went into the protected zone without being detected by the authorities.
"It is crucial to work with fishing communities to understand where, when and why people fish illegally – and how we can improve deterrence," said another of the study’s author, Tom Letessier.
"For example, we found fishers had very different ideas of the fines they could face, and some felt there were very unlikely to be caught – so improving awareness of the sanctions, in addition to increasing the probability of being caught, could be beneficial."
The management of the MPA must adapt to changing circumstances and the actual behaviour of locals, the scientists conclude. They recommend interacting with fishermen to find out what pressures they face and what motivates them to illegally take species from the MPA, and increased use of satellite tracking of vessels.
Despite its beneficial impact on biodiversity in the Indian Ocean, the BIOT MPA is highly contentious.
The Chagos Islands, formerly part of Mauritius when it was a British colony, were not handed over to the island nation upon its independence. Instead, the authorities forcibly removed about a thousand locals from the archipelago in the 1960s to allow the United States to build a military base.
The Permanent Court of Arbitration ruled in 2015 setting up the MPA violated the UN Convention on the Law of the Sea, as it contravened Mauritius’s fishing rights.
Mauritius has also obtained a judgement by the International Court of Justice and a UN General Assembly resolution which confirms the UK’s administration of the Chagos islands is unlawful and orders Britain to give the archipelago back to Mauritius.
The Independent also revealed in 2014 that despite creating the MPA to ostensibly protect the waters around the BIOT, the boat which patrols the territory and US naval vessels at the military base have both been discharging waste into the ocean for decades.
The Diego Garcia base is also excluded from the conservation rules in the rest of the MPA.
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