Two dead dolphins 'forgot to breathe after taking heroin substitute following zoo's weekend-long rave'

Shadow and Chelmers died within five days of each other at Connyland in Switzerland

Bosses at the park had rented land near the dolphins' training pool to rave organisers

Two dolphins who died a slow, agonising death at a zoo after it hosted a rave were probably killed by a party-goer's heroin substitute, according to a leaked toxicology report.



The dolphins, called Shadow and Chelmers, died within five days of each other at a zoo in Switzerland last November.

Bosses at the park had rented land near the dolphins' training pool to organisers of a weekend rave party for thousands of clubbers.



Slow and painful death: A toxicology report concluded that Shadow was probably killed by a party-goer's heroin substitute

Before the party: Shadow had been one of the star attractions at the Connyland zoo in Switzerland

Prosecutors said at the time that they were considering negligence charges because they believed antibiotics given by zoo vets were to blame for the deaths at Connyland in Lipperswil.

But another toxicology report carried out at the time, leaked to Swiss media, has raised new questions about what happened.



Tests conducted by the forensics institute in St Gallen found the heroin substitute Buprenorphin in the animals' urine.

Dutch marine biologist and dolphin expert Cornelis van Elk said: 'Opiates are extremely dangerous for underwater mammals and would never be used in any legitimate treatment.



'The reason is that dolphins are conscious breathers which means they actively decide when to come to the surface to breathe, for which they need to be awake.



'Even when sleeping, there is part of the brain that automatically controls the breathing instinct in the same way as it does for people when asleep.



'Drugging them with opiates could well cause this part of the brain to switch off with fatal consequences.'



Putting on a show: Bosses at the park had rented land near the dolphins' training pool to organisers of a weekend rave party for thousands of clubbers

It was originally suggested by keepers that rave-goers could have caused the death by feeding the dolphins illegal recreational drugs but prosecutors had rejected this, blaming the zoo's vets.

Connyland spokesman Erich Brandenberger said it would ask questions about why the initial theory had not been followed up and why the zoo's vets had been blamed.

Shadow and Chelmers died after what staff described as a 'drawn out and painful' death.



Connyland keeper Nadja Gasser told local media: 'The death went on for over an hour.

'It was horrendous. I have not been able to sleep since.



'When we went to start the dolphin training we noticed the same thing that had happened to Shadow was happening with Chelmers.



Investigation: Prosecutors initially considered negligence charges because they believed antibiotics given by the zoo's vets were to blame for the deaths

'He was drifting under the water and was clearly in trouble and so we jumped into the water.

'We tried to hold him. He was shaking all over and was foaming at the mouth.



'Eventually we got him out of the water. His tongue was hanging out. He could hardly breathe.

'He was given adrenalin, but it didn't help.

'After an hour the dolphin died. '



Questions: Bosses at Connyland want to know why the zoo's vets were blamed for the deaths of Shadow and Chelmers

Furious animal activists say they warned both the marine park and local planners - who gave permission for the rave - of the dangers before the event.



They had been concerned that the high levels of noise could damage the marine mammals' immune system, sensitive sonar and hearing.