A Freshwater dolphin species has been declared extinct after desperate efforts to rescue it came too late.

One British zoologist yesterday described the loss of the Yangtze River dolphin as a "shocking tragedy". It is the first extinction of a large vertebrate for more than 50 years.

Experts say human activity killed off the white long-beaked dolphin, which grew to eight feet and weighed 500lb. The animal is the first cetacean, the group that includes whales and porpoises, to vanish as a direct result of human influence.

In the 1950s the dolphin, unique to China's Yangtze River, also known as the Baiji, had a population of thousands.

Over the next five decades its numbers declined as China modernised and made heavy use of the river for fishing, transport, and electricity generation.

During Mao Ze-dong's "Great Leap Forward", traditional veneration of the Baiji - nicknamed "Goddess of the Yangtze" - was denounced and the dolphin hunted for its flesh and skin.

Industrial pollution, depleted food due to overfishing, loss of habitat, and the construction of the Three Gorges Dam put further pressure on the dolphin.

Stocks of some of its prey species collapsed to one thousandth of pre-industrial levels.

In the crowded Yangtze, many dolphins died after becoming entangled in fishing nets and being prevented from surfacing for air. Noise pollution also caused the animals, which navigate by sonar echo-location, to collide with vessels and get caught in propellers.

Surveys of the Yangtze River dolphin showed that by 2006 its population had fallen to 17.

Zoologists developed a scheme to save the Baiji by setting up a conservation reserve in a 21km oxbow lake which was once part of the Yangtze. The idea was to capture a few individuals and move them to the lake, where they could be cared for.

But a six-week search for the animals yielded not a single one. The experts were forced to concede the dolphin was extinct.

Dr Sam Turvey, from the Zoological Society of London, who led the search, said: "The loss of such a unique and charismatic species is a shocking tragedy."