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.
Davina the dolphin has successfully been released into the sea and is "safe and well", an RNLI spokeswoman has told ITV News.
Once she had been stretchered onto a lifeboat, Davina was transported from the sandbanks of the River Dee to deeper waters at Rhyl Flats.
Watch the Flint and Rhyl RNLI lifeboat volunteers and British Divers Marine Life Rescue take Davina to safety:
The dolphin that got stranded on sandbanks in the River Dee, Chester, is being returned to sea.
Initially named "Dave" by rescuers and then re-named "Davina" after being identified as female, the dolphin was rescued by volunteers from the Royal National Lifeboat Institution this morning.
RNLI lifeboat operations manager Alan Forrester said: "She will probably be much too heavy to lift aboard Rhyl RNLI lifeboat so Rhyl will escort us out to sea.
"The dolphin will be released around the North Rhyl Flats as, if it is set free in any shallow waters, there are fears it will become stranded again."
A dolphin that was spotted swimming in the River Dee, Chester, is set to be returned to open waters.
It is believed the mammal "was probably chasing fish in from the sea and then got caught up in the tidal system" when it became stuck in the river, according to a marine charity.
The Royal National Lifeboat Institution said the dolphin was stranded this morning and has now been taken by boat to the Irish Sea where it will be released.
A dolphin spotted swimming in the River Dee "was probably chasing fish in from the sea and then got caught up in the tidal system," according to a marine charity.
Stephen Marsh, operations manager at the charity British Divers Marine Life Rescue, said tides at this time of year can be both very high and very low and that is probably confusing the dolphin, which is more used to much deeper water.
Mr Marsh said such an event is quite rare, adding that they would step in to take it back out to sea if it does get into trouble.
However, he said it looks healthy and they hope it will find its own way out.
Moving footage has emerged of a dolphin that strayed into a Welsh river and into English waters in Cheshire.
The footage is understood to have been captured on Monday at Connahs Quay Docks in Flintshire.
From there the dolphin was seen further up the river in Saltney, near Chester and was most recently seen near Chester Racecourse.
Marine experts think the common dolphin, which is usually more at home in the deep seawater of the Bay of Biscay, must have been chasing fish up the River Dee in North Wales.
The dolphin is being monitored by a marine charity in case it gets stranded on a sandbank.
A dolphin is being monitored by a marine rescue charity after swimming miles up the River Dee in Flintshire.
The mammal was spotted by the public in Connah's Quay docks on Monday but swam up river to Saltney, near Chester.
It became stranded briefly on Tuesday afternoon after turning to make its way to Flint and back towards the sea.
A video showing dolphins being rescued from shore by beachgoers in Brazil has become an internet sensation.Read the full story ›