By Mark Dummett
BBC News, Dhaka
Bangladesh has asked conservationists to stop attaching radio collars to wild tigers while it investigates the deaths of two of the endangered animals.
Conservationists say Sundarbans tigers are under pressure
Wildlife photographer Sirajul Hossein said two Royal Bengal tigers collared by the Sundarbans Tiger Project had died soon afterwards.
The project defended its work, saying the tigers probably died of old age.
The collars are used to track the tigers so that their movements and behaviour can be better understood.
Royal Bengals are the second largest tiger subspecies and the most common.
'Tranquilisers not controversial'
Mr Hossein said the tigers may have died because of a drug used to sedate the animals so that the radio-collars could be fitted.
"People should be careful of any kind of invasive method, such as injecting the tiger with chemicals," Mr Hossein told the BBC.
Suspending the collar programme would be a 'disaster'
"We just don't know what the affect of Telazol is on the tigers."
He also said the drug could provoke "abnormal behaviour", even leading to attacks on people, but did not provide any evidence that this had happened.
Adam Barlow of the Sundarbans Tiger Project, which monitors and protects the 300-500 tigers of Bangladesh's giant Sundarbans mangrove forest, dismissed Mr Hossein's theory of why the tigers died.
He said he uses standard techniques employed by tiger experts around the world.
"Telazol has been used on wild tigers in Nepal, Thailand and now Bangladesh. No adverse effects from the drug's metabolism were observed."
"There is little, or possibly no, evidence available that categorically proves Telazol to be harmful to tigers," he said.
According to Raghu Chundawat, a Delhi-based wildlife scientist who is not connected to the project, any long-term suspension of the radio-collar programme would be a "disaster" for the Sundarbans, and doubts about the safety of the drugs are "absolute nonsense".
"The use of tranquilisers is not controversial. When this is done properly there is no problem," he said.
'Worth the risk'
A spokesman for Fort Dodge, the company which makes Telazol, said it had not performed any safety studies on its use on tigers, and does not market or recommend Telazol for this purpose.
"Telazol is a veterinary prescription-only anaesthetic licensed in numerous countries exclusively for use in domestic dogs and cats," Tom Lenz, the vice-president of Fort Dodge's Animal Health department said.
"Telazol has been manufactured and sold for 25 years, during which time the product has maintained an excellent safety record," he said.
The tigers roam through much of the Sundarbans
The longest running field study of tigers has taken place in eastern Russia. There, the US-based World Conservation Society says it has sedated and radio collared over 60 tigers with no ill-effects.
"With trained professionals, the risk of capture and immobilisation is low, although it will never be zero," director Dale Miquelle said.
"Based on our 16-year project in Russia, we believe the information gained is worth the risk."
Adam Barlow, of the Sundarbans Tiger Project, agrees.
While Bangladesh's Forestry Department looks into the allegations, he says he has stopped work on a project to attach a radio-collar to a tiger that has killed over 60 domestic animals and one person since last April.
Mr Barlow hopes that once it is collared the people living in Chandpai village will be able to follow its movements and so prevent any more attacks.
He says that a similar project to collar lions in Kenya has greatly reduced attacks on livestock and lions there.