For Nilantha Kodithuwakku, a naturalist involved in whale and dolphin-watching operations, it’s always a spectacular scene to witness pods of playful dolphins jumping and spinning in the air. But occasionally the scene he encounters is of dolphin carcasses, either floating or washed ashore, with the tail flukes missing. Charles Anderson, a marine biologist based in the Maldives, is familiar with this grisly phenomenon.
“Dolphins often get entangled in drifting gillnets used in tuna fishery,” he told Mongabay. “The fishermen then cleanly cut off the flukes to separate the carcasses from their fishing gear.”
For as long as humans have been fishing, cetaceans like dolphins and whales have been getting entangled in nets. But the problem was only widely recognized as one of the biggest threats to the survival of these species, particularly dolphins, in the 1980s, with the widespread use of gillnets.
Now, a new study led by Anderson estimates that as many as 4.1 million small cetaceans were likely killed in the Indian Ocean as a result of such gillnets from 1950 to 2018. Researchers estimate the abundance of small cetaceans in the Indian Ocean may now be around 13% of pre-fishery levels.