Changing distribution and abundance of Swan Goose Anser cygnoides in the Yangtze River floodplain: the likely loss of a very important wintering site

Abstract

SummaryVirtually the entire population of the globally ‘Vulnerable’ Swan Goose Anser cygnoides winters in the Yangtze floodplain. Historically, the species was widely distributed throughout the floodplain but now approximately 95% of the population is confined to three closely-situated wetlands in Anhui and Jiangxi Provinces. Recent counts indicate that at one of these sites, Shengjin Lake (in Anhui), a decline of about 10,000–20,000 birds, to about 1,000 currently, has taken place during the last five years. The likely cause of the decline in Swan Goose abundance at Shengjin Lake is the recent decrease in submerged vegetation, particularly tuber-producing Vallisneria which is the species’s main food; this decrease has been linked with the introduction of intensive aquaculture in the main areas used by Swan Geese within the lake. Earlier range contractions in the Yangtze floodplain may also be linked to reductions in submerged vegetation cover at other sites, where intensive aquaculture has also been implicated. Changes in lake hydrology following construction of the Three Gorges Dam may also have adversely affected submerged vegetation productivity. Key information needs for the effective implementation of conservation measures for Swan Goose include an understanding of (1) the fitness consequences of Swan Geese being forced to switch to different foods; (2) how aquaculture can be managed to minimise impacts on submerged vegetation; (3) the impact of changing lake hydrology on key Swan Goose food plants; and (4) the optimal management of wetlands to ensure that adequate food is both produced during the summer period and is available throughout the winter.