Yangtze River dolphin maintained large range before extinction

Journal Watch Online 18 May 10;

The range of the Yangtze River dolphin did not shrink dramatically in the years leading up to the species’ extinction, as people previously believed, scientists say in the Proceedings of the Royal Society B.

This freshwater mammal, also known as baiji (Lipotes vexillifer), used to occupy China’s Yangtze channel and two nearby lakes. As a result of fishing and industrialization, the dolphins’ numbers dwindled. During its final years, the species was thought to have become restricted to only a few “hotspots” along the river.

Researchers interviewed 599 people in fishing communities around the species’ historical habitat and examined other records of baiji sightings. Contrary to expectations, fishermen had continued to see baiji throughout the middle and lower regions of the Yangtze channel and in one of the lakes during the decade before the species disappeared.

Right now, the International Union for Conservation of Nature (IUCN) determines species’ extinction risk based partially on whether their ranges are becoming smaller or fragmented. But the case of the Yangtze River dolphin shows that some mobile animals may not show signs of range reduction “even up to the time of extinction,” the team writes. – Roberta Kwok

Source: Turvey, S.T. et al. 2010. Spatial and temporal extinction dynamics in a freshwater cetacean. Proceedings of the Royal Society B DOI: 10.1098/rspb.2010.0584.