Fish diet heats up marine biodiversity hotspot
Scientists have discovered a never-before-seen biodiversity pattern of coral reef fishes that suggests some fishes might be exceptionally vulnerable to environmental change. A new study shows plank
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A massive study of nearly 1800 tropical coral reefs around the world has found that marine reserves near heavily populated areas struggle to do their job – but are a vast improvement over having no protection at all.
Professor Josh Cinner from the ARC Centre of Excellence for Coral Reef Studies at James Cook University led a team of 37 scientists 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 Professor Cinner.
The scientists also studied how differences in ecological conditions between marine reserves, where fishing is prohibited, and places open to fishing changed as human pressures increased. “This tells you where you can get the biggest impact from implementing conservation,” said Professor Cinner.
“A really novel and exciting part of 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.
For example, on reefs subject to high human pressure, marine reserves had five times more fish than openly fished reefs – a benefit that can spillover into the depleted fisheries in surrounding areas.
“However, top predators such as sharks were a different kettle of fish,” said co-author Dr Aaron MacNeil from Dalhousie University.
The scientists encountered top predators on less than 30% of their surveys conducted all across the globe, and very rarely in locations where human pressures were high.
“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 Dr MacNeil.
Dr Michele Barnes from the ARC Centre of Excellence for Coral Reef Studies at JCU said that in many places, social, economic, and cultural realities mean that marine reserves that entirely prohibit fishing are not an option.
“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.
Professor Cinner said the study makes clear the benefits and limitations of implementing key coral reef conservation strategies in different types of locations. “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,” he said.
Citation: Cinner JE, Maire E, Huchery C, MacNeil MA, Graham NAJ, Mora C, McClanahan TR, Barnes ML, Kittinger JN, Hicks CC, D’Agata S, Hoey AS, Gurney GG, Feary DA, Williams ID, Kulbicki M, Vigliola L, Wantiez L, Edgar GJ, Stuart-Smith RD, Sandin SA, Green A, Hardt MJ, Beger M, Friedlander AM, Wilson SK, Brokovich E, Brooks AJ, Cruz-Motta JJ, Booth DJ, Chabanet P, Gough C, Tupper M, Ferse SCA, Sumaila UR, Pardede S, Mouillot D (2018) Gravity of human impacts mediates coral reef conservation gains. Proceedings of the National Academy of Sciences 115:E6116-E6125
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The researchers evaluated fish biomass and the presence of top predators on coral reef sites across 41 countries, states, and territories. They used a new way of measuring the human pressures, such as fishing and pollution, to study the effects these are having on fish on the world’s reefs. They developed a ‘human gravity’ scale that calculates factors such as human population size, distance to reefs, and the transport infrastructure on land – which can determine reefs’ accessibility to fishermen and markets.
Conservation scientists say there needs to be a new approach to protecting offshore marine reserves.
Illegal fishing in marine reserves will be a major focus at the IUCN World Parks Congress, which has opened in Sydney.
Researchers at the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University, who are attending the conference, have found a way to predict illegal fishing activities to help authorities better protect marine reserves.
Marine reserves are the most common strategy used to protect and maintain marine ecosystems around the world.
The International Convention of Biological Diversity aims to have 10 per cent of the world’s marine areas protected by 2020.
Many countries are contributing to this target by protecting remote, offshore areas. For example, the United States recently created the world’s largest fully protected marine reserve, covering almost 1.27 million square kilometres in the central Pacific Ocean.
But scientists are concerned that while a great deal of effort is being made to create reserves, many countries are simply not able to enforce the laws that are supposed to protect them.
The majority of fishers obey the law, but some don’t.
“The success of protected areas depends on whether people comply with the regulations,” says Professor Joshua Cinner from Coral CoE.
“Enforcement and compliance issues for large off-shore marine parks are fundamentally different to near-shore protected areas,” Professor Cinner says.
He explains that the biggest problems facing countries trying to enforce offshore marine reserves is their distance from land and the difficulty and cost of patrolling large tracts of ocean.
“The distances to these areas can be very large. They are a long way from prying eyes and quite often the regulations are such that you have to actually catch people illegally fishing to prosecute them,” Professor Cinner says.
“It can be extremely difficult for authorities to catch illegal fishers in the act.”
In a bid to combat the problem, researchers at Coral CoE examined five years’ worth of data collected from the World Heritage-listed Cocos Island National Park, a unique marine protected area in the Pacific Ocean about 500 kilometres off the west coast of Costa Rica.
From the records they were able identify illegal fishing patterns and predict both when and where illegal fishing was likely to happen.
They found that illegal fishing was concentrated in a few ‘hotspots’ and really ramped up during specific lunar phases of some months.
Professor Bob Pressey, also from Coral CoE, says authorities could use this knowledge to match patrols to the time and place when illegal fishers are most likely to be in action.
“Using a targeted approach helps authorities catch and deter illegal fishers, while saving money on patrols,” Professor Pressey says.
“Rather than just hoping you can catch illegal fishers effectively by random patrols, we have used previous patrols to look for patterns which tell us when and where people fish illegally,” adds Professor Cinner.
Study lead author, Coral CoE PhD candidate, Adrian Arias says the model of predicting illegal patterns from old records can be used to increase the success of patrols in other locations.
“Our research in Costa Rica showed how a systematic and periodic analysis of patrol records can help to increase the probability of catching illegal fishers. This could be done pretty much anywhere that patrol data are available,” he says.
Professor Cinner adds that by better targeting limited resources, authorities have a greater chance of successfully protecting marine parks.
“Targeting resources is particularly important for developing countries such as Costa Rica, which have taken on the conservation challenge but don’t have the same funding to ensure compliance as a country such as Australia.”
Optimizing enforcement and compliance in offshore marine protected areas: a case study from Cocos Islands, Costa Rica by Adrian Arias, Robert L. Pressey, Rhondda E. Jones, Jorge G Alvarez-Romero and Joshua E. Cinner is published in the journal, Oryx. http://dx.doi.org/10.1017/S0030605314000337
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James Cook University Townsville
Queensland 4811 Australia
Phone: 61 7 4781 4000