Visitation Aspect of Mergansers (Mergus spp.) in the Nakdong Estuary, Busan, Korea

This study was conducted to investigate the migration pattern of Mergansers (Mergus spp.) migrating to Nakdong estuary through the analysis of the long-term findings between the early 1990s (May, 1989∼April, 1993) and the mid-2000s (May, 2002∼April, 2008). For 10 years of research period, the total of 2,064 individuals of Mergansers (Mergus spp.) representing 3 species were observed at Nakdong estuary. Specifically, Red-breasted Merganser were 1,770 individuals, and Common Merganser were 214 individuals, and Smew were 80 individuals. Smew has decreased from 45 to 35 individuals, and 214 individuals of Common Merganser have been observed only in the early 1990s. In comparison to the monthly migration status, there was significant difference between December (P<0.010) and January of following year (P<0.011). With regard to the migration status of Red-breasted Merganser by area, the means of the individual numbers observed in five sites was 49.17: 74.00 individuals in Daema-deung (DMD), 95.00 individuals in Jangja · Sinja-do (JJ · SJD), 40.17 individuals in Saja-do · Doyo-deung (SJDYD), 11.50 individuals in Lower Ulsuk-do (LUD), and 25.17 individuals in Ulsuk-do (USD). There was statistically significant mean difference of individual numbers among five sites (P<0.001). With regard to the monthly total number of individuals, the observed numbers of Red-breasted Merganser were 20.5 individuals (February in following year) and 30.17 individuals (March) in Jangja · Sinja-do; 18.67 individuals (December) in Daema-deung; 11.5 individuals (February in following year) in Saja-do · Doyo-deung. The observed numbers of Smew were 1.83 individuals (March in following year) in Ulsuk-do; 0.33 individual (January in following year) in Daema-deung. In the 2000s, the individual number of Red-breasted Merganser in Nakdong estuary has even increased. This might indicate that they have well adapted in the relatively shallow waters. The sites where Mergansers (Mergus spp.) are frequently observed were upper and lower part of river channel between Daema-deung and Jangja-do, which is used for small craft; the lower part of Myungji residential areas, which located at the left side of Daema-deung. These sites have relatively shallow waters and little access by ships. Therefore, careful attention and interest should be paid to the security of enough feeding places for Mergansers (Mergus spp.). In addition, it is required to prepare for measures to maintain sound ecosystem of the site and to preserve the habitat for them.