A spokeswoman said the survey meant they would be able to build up an effective conservation programme.

The team of biologists spent seven weeks travelling nearly 1,500 kilometres down the Indus river in search of this unique species of dolphin.

Satellite technology

The team spotted more than 960 dolphins and used satellite technology to precisely record their location.

Taking into account a few inaccessible stretches of river they concluded that at least 1,000 dolphins were living in the lower reaches of the river.

The WWF said this was considerably more than they had estimated.

However it is still a worryingly small number considering the Indus River dolphin, described by one scientist as a living fossil, occurs only in Pakistan.

Dolphins trapped

The WWF says it is concerned about the continuing drought in Pakistan, which has caused the Indus river to fall dramatically and could have a serious affect on the population.

The increasing number of barrages along the river in Sindh and Punjab provinces have trapped the dolphins in small areas.

The conservationists said they would be exploring the problems caused by the barrages and the effect on the dolphins gene pool.

The WWF has been rescuing dolphins which have strayed into irrigation channels and are now looking at the possibility of putting satellite tracking devices on those they put back into the Indus, to follow their movements.