Researchers estimate that hundreds of thousands of sharks are killed yearly in the Indian Ocean with devices used to catch tuna.
Tuna tend to gather around objects floating in the sea. Over the last two decades, fisheries have attracted tuna by leaving masses of bamboo poles and netting, called fish aggregating devices (FDAs) to drift in the ocean. Fishing boats later return to catch the fish caught in the nets.
The authors of the study attached satellite tags to 29 silky sharks in the Mozambique Channel and near the Republic of Seychelles to find out if sharks could become entangled.
Silky sharks are one of the most abundant sharks in the pelagic zone, and can be found around the world in tropical waters. Highly mobile and migratory, this shark is most often found over the edge of the continental shelf down to a depth of 164 ft.
The movements recorded by the tags suggested that four of those sharks became caught in the nets near the surface, the team reports in Frontiers in Ecology and the Environment. Divers also visited 51 FADs and found that 35 percent of them had entangled one or more silky sharks.
The researchers estimate that FADs in the Indian Ocean kill about 480,000 to 960,000 silky sharks per year. The authors recommend for fisheries to replace the netting with biodegradable ropes.