Dalhousie study reveals sharks 'functionally extinct' in 20% of world's coral reefs
Global study monitored 371 reefs in 58 countries over four years
A new global study authored by a Dalhousie University professor has determined that sharks are "functionally extinct" in nearly 20 per cent of the world's coral reefs, raising concerns about what it might mean for those coastal ecosystems.
"That was surprising. We expect, as a condition without humans, that there should be sharks on every reef in the world," said Aaron MacNeil, the lead author of the study, which was published Wednesday in the journal Nature.
"To find 20 per cent of the reefs that we surveyed didn't have sharks is very concerning."
MacNeil, a biology professor at Dalhousie University, said Tuesday the study was inspired by initial research from Ransom Myers and Julia Baum at Dalhousie about 20 years ago. That work showed a decline in open-ocean shark populations.
He said since then, not much research has been done in other regions — until now.
The global study, which is the first of its kind, was launched in 2015 by the Paul G. Allen Family Foundation and a team of researchers brought together under an initiative called Global FinPrint. The team studied 371 reefs in 58 countries.
The study monitored coral reefs — in the western Atlantic, the western Indian Ocean, the Indo-Pacific and the Pacific — to determine how reef sharks impacted the delicate ecosystems and to inform future conservation efforts.
Researchers used baited remote underwater video cameras to record sharks and other sea life on coral reefs. Between 30 and 100 cameras were set up on each reef, recording one hour of footage each. The team captured more than 15,000 hours of video over four years.
The research revealed that there are essentially no sharks in reefs of the Dominican Republic, the French West Indies and Windward Dutch Antilles in the Caribbean, and in Kenya, Vietnam and Qatar.
The study said among those nations, only three reef sharks were observed during more than 800 survey hours.
"These nations are places where we're saying reef sharks are essentially functionally absent from the ecosystem. They play no role in the ecosystem and they're functionally extinct," MacNeil said.
He said the loss of reef sharks has been caused by high population densities near coastal areas, lack of shark fishing regulations, and overfishing and the destructive practices that come with it.
But MacNeil said the research also identified nearly 20 nations where reef shark populations are doing well, such as in Australia, the Bahamas, French Polynesia, the Maldives and the United States.
Reef shark conservation
"Our results show that reef sharks can, under the right conditions, live alongside people and thrive just fine," said Demian Chapman, one of the lead researchers on the study.
Chapman, a biology professor at Florida International University, said people are a part of the problem, but they're also a part of the solution.
He said the study revealed a few ways that countries can protect reef shark populations, including:
- Establishing shark sanctuaries where commercial shark fishing and trade is banned.
- Mandating catch limits on shark fishing so ecosystems can replenish.
- Closing large, designated areas of water where all fishing is banned to promote ecosystem growth.
- Prohibiting or redesigning shark fishing gillnets and longlines, which can inadvertently capture other marine life in their path.
"The Global FinPrint results show this portfolio of approaches, and countries can actually grab from whichever ones suit best their local communities so that they can have benefits for both the reef sharks and the people that live alongside them," Chapman said.
He said during the research, people around the world were enthusiastic about making a difference for reef sharks.
"We're really, really hopeful. We're going to continue our work with governments to put these policies in place to restore and better protect reef sharks all over the world," Chapman said.
Mike Heithaus, another lead research on the study, said saving reef sharks is necessary to maintain important ecosystems.
"If you look around the world, whether it's on land, in lakes and rivers or in the oceans, when you lose big predators, bad things tend to happen to the ecosystem in general," said Heithaus, dean of the College of Arts, Sciences and Education at Florida International University.
He said based on detailed studies of other ecosystems, lack of sharks can have a negative impact.
"If we were to lose sharks from these systems, you could destabilize the whole ecosystem and have negative impacts that are not just to nature but also to fishermen and people who rely on these coastal ecosystems that we studied," he said.
Heithaus said the next step is to investigate how the loss of sharks destabilizes the reef ecosystem.
"For us, the future is very hopeful," he said.
"We want to focus on those areas where we can have the biggest impact, learn how important those sharks are to those reefs so we can have a better foundation for conservation ... so that we have these animals in these ecosystems supporting the communities that rely on them for generations to come."
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