Population Size and Sex Ratio of Wintering Scaly-Sided Merganser Mergus squamatus in the Poyang Lake Water System, Jiangxi Province, China

The line transect method was used to examine the population size and sex ratio of the scaly-sided merganser Mergus squamatus (the merganser) in four rivers of the Poyang Lake water system, Jiangxi province, China. Spatial and temporal variations in population size were ascertained for this endangered species. The Xiuhe, Fuhe and Raohe river systems exhibited large steady populations, with the maximum size ranging from 25 to 68 individuals for each river. Restoration and maintenance of suitable habitats for the scaly-sided merganser is imminent as the species is at risk of extinction due to its small population size. The total sex ratio of the merganser during the study period was 0.397 (n = 790) and the average sex ratio was 0.43 ± 0.26 (n = 148) for each group, similar to the results obtained in previous years in Jiangxi province (0.378-0.4588). These data indicate that the wintering sex ratio of the merganser has been relatively steady over this period. The current results also revealed temporal and spatial variation in the sex ratio of mergansers, which is common among other duck species. The lower sex ratio in Xiuhe River indicated that the population in this river may include more sub-adults. Long-term data should be collected to test whether female mergansers are more likely to migrate north. The sex ratio of the merganser exhibited a tendency to decrease gradually from the early to late stages in each river, although only the Raohe River exhibited a significant difference among three stages, possibly due to differences in sexual migration time and mortality. We did not detect significant differences in the sex ratio of the scaly-sided merganser among different group sizes.