Gangs of illegal divers, equipped with motorboats and scuba equipment, can hoover up sea cucumbers in huge quantities, operating with impunity in a country that lacks the capacity to enforce its fishing regulations.
But for every traded shark fin there must be a shark hunter, and we rarely get to hear the human side of the story.
Our research, published this week in the journal Geoforum, shows how Chinese demand for shark fins and sea cucumbers has affected traditional fishers in Madagascar.
The Vezo live along the country's southwest coast and derive their living entirely from the sea. Most of the fishing methods they use have remained unchanged for generations. Their boats have no motors, they dive without tanks, and many still make their nets by hand. What has changed is trade.
Growing demand driving new migrations
Two generations ago most Vezo fished purely for their own plates, but global demand for seafood has brought them firmly into the cash economy. Having exhausted the world's more accessible waters, Chinese trade networks for shark fin and sea cucumber reached the region in the 1990s.
For Vezo fishers, animals they had previously ignored or avoided became incredibly valuable. But just as had happened elsewhere, they soon got fished out, and the fisheries collapsed. Undeterred, the Vezo simply moved along the coast, following the dwindling stocks into unfished waters.
I carried out the research with Dr Garth Cripps, who joined a group of Vezo fishers on their migration from the village of Ampasilava on the island continent's southwest coast. Their destination - the rich fishing grounds of the Barren Isles, a remote archipelago about 300 miles north.
Travelling in a laka, a traditional wooden sailing canoe just three feet wide and 20 feet long, the group made landfall on islands and in mainland villages along the way, where Garth discussed the migration and its impacts with both migrant and resident fisher communities.
The conditions Garth heard about - and encountered - when he reached the Barren Isles astonished him.
Some islands were just subtidal cays, simple sand bars that were completely inundated in the highest tides, but that didn't stop hundreds of migrants from settling there for months at a time - when the tides came in they would simply pack up their camps in their laka, drop anchor, and sit in their boats till the waters receded. So what would drive people to endure such conditions?
"Here the Vezo live on the very margins of society, leading a traditional life in the most remote places yet highly connected to global markets", says Garth.
We found that the migrants were affected by both 'push' and 'pull' factors. On the push side, overfishing and a rapidly growing coastal population made life in their home villages extremely difficult. But it was the lucrative nature of shark fin and sea cucumber that really drove them northwards, to waters where they could still be found.
Garth found that a single sea cucumber could fetch over £8 while 1kg of high quality shark fin could reach almost £70, enormous riches when the average income in the migrants' home villages is just £1.16 a day.
"While life on the islands is tough, the migrants face a bleak life in their home villages where fish stocks are close to collapse. Migration has become a critical way to make enough money so that they can look after their families", says Garth. "Stopping migration would just make fishers even poorer."
The impacts of the migrants are a concern to conservationists, since the Barren Isles are one of the richest and most intact marine ecosystems in all of Madagascar. However the area also faces a bigger problem - gangs of illegal divers, equipped with motorboats and scuba equipment, who can hoover up sea cucumbers in much greater quantities. Though their actions are illegal, they operate with impunity in a country that lacks the capacity to enforce its fishing regulations.
Expanding marine protected areas
In December 2014, Madagascar's president Hery Rajaonarimampianina declared his government's bold and ambitious new vision - to triple the coverage of the country's marine protected areas. Marine protected areas come in various forms, but can roughly be divided into strict, 'no-take' areas where all fishing is outlawed, and those where sustainable forms of fishing are allowed.
While no-take areas are generally implemented by governments and don't always account for the needs of local fishers, a new, more participatory model has been spreading across Madagascar and the Western Indian Ocean over recent years. Locally managed marine areas (LMMAs) place the power to decide on fisheries management in the hands of the fishers themselves, and have so far proved remarkably effective.
Now the largest LMMA in the Indian Ocean is being implemented in the Barren Isles and the model faces its sternest test. Can migrant and resident fishers work together to keep the illegal divers out?
The paper: 'Human migration and marine protected areas: Insights from Vezo fishers in Madagascar' is by Garth Cripps and Charlie J. Gardnera, and is published in Geoforum.
Also on The Ecologist: 'Sustainable abundance - rebuilding fisheries to support coastal communities in Madagascar' by Alasdair Harris.
Dr Charlie Gardner is an interdisciplinary conservation scientist and practitioner with a particular focus on Madagascar and the Western Indian Ocean. He is an Honorary Research Fellow at the Durrell Institute of Conservation and Ecology (University of Kent), and his principal research interests include protected area management, small-scale fisheries, and approaches to span the divide between conservation science and practice.
Books: Charlie's book 'Life Amongst the Thorns', co-authored with the photographer Louise Jasper, seeks to highlight the incredible biodiversity and conservation issues of Madagascar's spectacular spiny forest.
Blue Ventures: Charlie is a long-term partner of, and adviser to, Blue Ventures, which develops transformative approaches for catalysing and sustaining locally led marine conservation. They work in places where the ocean is vital to local cultures and economies, and are committed to protecting marine biodiversity in ways that benefit coastal people.