Marine reserves near heavily populated areas face stress: Study

MELBOURNE: Marine reserves near heavily populated areas struggle to provide habitat to fish and other underwater organisms, but are still better than having no protection at all, a study reveals.


Scientists, led by Josh Cinner from James Cook University in Australia, conducted a detailed study of nearly 1800 tropical coral reefs examining the effectiveness of different reef conservation strategies.


"Fish stocks were extremely depleted on reefs that were accessible to large human populations. Compared to marine reserves far from these human pressures, reserves near high human pressure had only a quarter of the fish and were a hundred times less likely to have top predators such as sharks," said Cinner.

To calculate the differences in ecological conditions with respect to human pressures, the scientists studied the differences between marine reserves which were open to fishing and the ones which were not.

"This tells you where you can get the biggest impact from implementing conservation," said Cinner.

"Our study found that the greatest difference in fish biomass between marine reserves and places open to fishing was in locations with medium to high human pressure. This means that, for most fisheries species, marine reserves have the biggest bang where human pressures are medium to high," he said.

The study affirmed that on reefs subject to high human pressure, marine reserves had five times more fish than openly fished reefs - a benefit that can spill over into the depleted fisheries in surrounding areas.

"However, top predators such as sharks were a different kettle of fish," said Aaron MacNeil from Dalhousie University in Canada.

The scientists, very rarely found top predators where the human pressures were high, accounting for less than 30 per cent in their surveys conducted across the world.

"You'd have to do about 200 dives to see a top predator in reserves with the highest human pressure. But where human pressure was low, you'd be likely to see predators more than half the time," said MacNeil.

"In many places, social, economic, and cultural realities mean that marine reserves that entirely prohibit fishing are not an option," said Michele Barnes from James Cook University in Australia.

"So, we also looked at how effective other forms of reef conservation were, such as restricting the types of fishing gear that people use. Our results were promising - these restrictions certainly had better outcomes than doing nothing, but not as good as marine reserves. They were a sort of compromise," she said.

"Our research shows where managers will be able to maximise certain goals, such as sustaining top predators or improving the biomass of key fisheries species, and likewise, where they will be wasting their time," Cinner said.

The study makes clear the benefits and limitations of implementing key coral reef conservation strategies in different types of locations.