Alison Wood from the Whale and Dolphin Conservation group has condemned the practice of using dolphin meat as shark bait as "wasteful and barbaric".
In an interview with ITV News, she said it was completely unnecessary to butcher the animals in this cruel, inhumane way.
"You can use fish guts, and all sorts of things to bait your hook, you don't need to use a sentient, intelligent animal like a dolphin. It is an awful waste. We are talking about a highly intelligent, social, feeling animal, and to see them hunted like this, is barbaric.
Slaughtering dolphins at sea is a cheaper alternative to other forms of bait for sharks, and the method of killing, harpooning, means that the dolphin can bleed for up to 15 minutes. The blood of the dolphin, then attracts sharks.
The illegal slaughter of dolphins for use as bait to hunt sharks is "an open secret" within fishing communities across Peru, according to marine conservation group Mundo Azul.
Working undercover with the group, British journalist Jim Wickens spent a week on board a shark fishing boat 100km off the coast of Peru, enduring rough seas and a near-death shipwreck incident in order to film the hunt.
For more than a decade scientists and environmentalists have been warning of a mass slaughter of dolphins around Peru.
Hundreds of fishing boats have been accused of killing the animals and using their fatty bodies as bait to catch sharks.
The killings, two or three per hunt, by hundreds of fishing boats around the country, add up each year to make it the biggest illegal slaughter of dolphins in the world, according to environmentalists.
ITV News has obtained footage that shows fishermen harpooning dolphins for bait. It's the first time this secret hunting has been filmed.
Science Editor Lawrence McGinty's report contains images you may find disturbing.
The footage, shot undercover by British journalist Jim Wickens, shows the hunting taking place, hundreds of miles off the coast of Peru.