Scientists say the market for shark fin soup is the likeliest reason for the sharp drop in blue shark numbers over the last 30 years.
They discovered that the sharks feed in exactly the same places in the ocean that long-line fishing boats operate, which means they get caught along with other target fish.
The researchers add that such regions are ideal places to implement so-called marine protected areas, where fishing is banned, to safeguard blue sharks and other vulnerable species.