An Introduction to the International Importance of Asan Bay to Waterbirds

Dr. Nial Moores, Birds Korea, August 31st, 2021

Figure 1. Location of Asan Bay and other wetlands known to be internationally important for shorebirds at the beginning of this century; with additional important wetlands surveyed by the Korea Shorebird Network (in the 2010s) marked with triangles. Adapted from Moores et al. (2016).


Asan Bay, centred at approximately 36°54’N, 126°53’E, is located on the west coast of the Republic of Korea (ROK), with main provincial jurisdiction divided between Chungcheongnam Province (Dangjin and Asan Cities) and Gyeonggi Province (Pyeongtaek City).

Asan Bay was first recognized as internationally important for waterbirds in 1988 (Long et al. 1988). Despite a series of large-scale reclamation projects and industrialization of much of the hinterland since that time, Asan Bay remains internationally important for a large number of tidal flat obligate waterbird species, including the globally Endangered Far Eastern Curlew Numenius madagascariensis and Black-faced Spoonbill Platalea minor, both species with high conservation profiles which have also proved attractive to ecotourists in other areas.

Maintenance of waterbird populations in Asan Bay will require formal protection of remaining tidal flats, combined with management of part of one or more reclamation impoundment area(s), to maintain foraging habitat for some species and to provide a secure high tide roost for others.

With appropriate management and investment, it should then be possible for local and national bodies to create a world class wetland reserve and visitor centre in Asan Bay, to take advantage of the Bay’s internationally important biodiversity, and to increase the possibility of registration of part of Asan Bay as a World Heritage property in 2025, as now being discussed. Economic and other benefits could then be derived from an increase in ecosystem services provided by the Bay, including an increase in green tourism; through an increase in local pride and the provision of high-quality green and blue spaces for local businesses and residents; and through the possibility of rebranding for those industries willing to invest in sustainable development, including the conservation of remaining internationally important wetlands in Asan Bay.

Tidal Flat Areas

At least until the 1950’s, Asan Bay was an extensive naturally semi-impounded tidal flat system, forming the southern part of the Gyeonggi Bay super-system (stretching unbroken north along the coast and around adjacent islands in present-day Gyeonggi and Incheon in the ROK to the Hwanghaenam coast of DPR Korea). Fed by several small rivers, the tidal flats of Asan Bay were contiguous with the Seokcheonri and Maehyangri tidal flats of Namyang Bay (now known as the Hwaseong Wetlands) to the north, and near-contiguous with a series of smaller bays along the north coast of what used to be known as the Seosan Peninsula.

In the mid-1980s, especially following completion of the Asan and Sapkyo reclamation barrages, the tidal flats of Asan Bay were further reduced in area and then separated into two component parts: those in the inner bay and in the outer bay.  Based on information provided to them, Long et al. (1988) estimated that 7,200ha of tidal flat remained at that time. Independent measurements using Google Earth historical imagery for 1984 provides an estimate of ~7,225ha of tidal flat at low tide at that time, with more than half of this (3,860ha) in the outer bay (Area 2 in Fig. 2), and the remainder in the inner bay area (Area 1 in Fig. 2).

Figure 2. Greater Asan Bay, 1984. 1= Inner bay; 2= Outer bay. For additional context, 3= Namyang Bay (now “The Hwaseong Wetlands”); 4= Asan Barrage and Lake; and 5= Sapkyo Barrage and Lake. Courtesy of Google Earth.

During the 1990s and early 2000s, almost all of the tidal flats in outer Asan Bay in Chungcheongnam Province were lost to reclamation, including through the reclamation north of Dangjin (centred at approximately 36°59’N, 126°38’E).  In the mid-1990s, a series of reclamation projects was also started in the inner bay area, coincident with the construction of the West Coast Highway bridge

Based on coarse measurements made through Google Earth (2021) by the author, Asan Bay currently contains approximately 2,640ha of natural or near natural tidal flat at low tide; three part-tidal reclamation impoundments, with intentionally porous seawalls and no permanent buildings, covering approximately 1,270ha (numbered 2 and 3 in Figure 3); and one immediately adjacent reclamation area with port facilities and about 165ha of tidal flat.  All the reclamation impoundments and approximately 525ha of the open tidal flat are within Pyeongtaek; the remaining 2,145ha of tidal flat are in Asan and Dangjin.

Figure 3. Asan Bay, 2021: 1= Main tidal flat used by foraging shorebirds; 2= Recently active reclamation impoundments, used by large numbers of roosting shorebirds; and by foraging Red-necked Stint Calidris ruficollis and Black-tailed Godwit Limosa limosa; 3= Older reclamation impoundment sometimes used as a high tide roost area (especially when conditions are unsuitable in Area 2); 4 =Asan Lake; 5 = Sapkyo Lake. Question marks indicate tidal flats which might or might not still support foraging shorebirds. Image courtesy of Google Earth.

Importance to Waterbirds

1980s & 1990s

Asan Bay was first identified as internationally important for waterbirds in 1988. Counts made during six visits between April 12th and May 29th found between 38,000 and 48,601 shorebirds, including between 15,000 and 22,000 Great Knot Calidris tenuirostris; almost 3,000 Bar-tailed Godwit Limosa lapponica; and 16 Nordmann’s Greenshank Tringa guttifer (Long et al. 1988).

Yi (2004) provides summaries of counts made by the National Institute of Environmental Research within the Ministry of Environment.  Between 1988 and 1996, Asan Bay supported a mean of 65,900 shorebirds annually during northward migration (making it the most important known site for shorebirds in the ROK during that period), and 6,700 shorebirds during southward migration.

Between 1997 and 2003, the annual mean of shorebirds in Asan Bay had fallen to 45,000 during northward migration but risen to 17,600 during southward migration (suggesting some variability in survey effort between years). In 1998, Moores (1999) counted a minimum 56,662 shorebirds in Asan Bay in three one-day surveys during northward migration, including 34,000 Great Knot in late April; and a flock of 18,282 Black-tailed Godwit Limosa limosa in mid-May, which also included a single Hudsonian Godwit Limosa haemastica (although not documented with an image, to date this remains the only ROK record); and 5,022 shorebirds in two one-day surveys during southward migration.

2000s & 2010s

In a one-day survey a decade later, on May 5th 2008, in large part because of access restrictions, our SSMP research team found only 9,570 shorebirds in Asan Bay, most within the newly-created reclamation impoundment, numbered 3 in Figure 3.  The only species recorded in a concentration of 1% or more of population was Mongolian Plover Charadrius mongolus (Moores 2012).

The Shorebird Network Korea then conducted one-day shorebird surveys in Asan Bay during northward migration in 2011, 2012 and 2013, and during southward migration in 2010, 2011, 2012 and 2013 (raw data compiled by coordinator Lee Kyung-Gu kindly shared with Birds Korea in 2016; Korea Shorebird Network 2013, 2014, 2016).  In total, the Shorebird Network Korea surveys recorded four species of shorebird in concentrations of 1% or more of a population: Mongolian Plover, Far Eastern Curlew, Common Greenshank Tringa nebularia and Terek Sandpiper Xenus cinereus. Oddly, even though the same Shorebird Network data were used, only two of these species were subsequently listed as meeting the 1% threshold by Ministry of Oceans and Fisheries (2017): Far Eastern Curlew and Common Greenshank.

2020 & 2021

A total of ten survey visits were made to the main reclamation impoundments (Areas 2 and 3 in Figure 3) between June 2020 and July 2021 by NM together either with Jung Hanchul (Gyeonggi KFEM and Birds Korea member) or Park Heajeong (Hwaseong KFEM) as part of research for the Hwaseong Wetlands Project, led by the EAAFP Secretariat and the Hwaseong Eco-Foundation (“Project Surveys”). Following formal permission from the site managers to survey, Project Surveys were conducted from roads within the main reclamation impoundments and were timed to coincide with spring high tides.

Our surveys were too brief and too infrequent to capture all of the migration through Asan Bay; and some parts of the bay were not even visited.   Nonetheless, the Project Surveys were able to find higher numbers of birds than most recent survey effort, due to the improved access, higher frequency of survey effort, and greater spread of survey dates. In addition, the Project Surveys were also able to confirm the continuing international importance of Asan Bay to a large number of tidal flat obligate species considered typical of Yellow Sea tidal flats (Table 1).

If data are available, the Ramsar Convention typically requires evidence that waterbirds are supported by a site “regularly” in internationally important concentrations before considering designation of Ramsar sites. The data for Asan Bay appear to be insufficient to develop 5-year geometric means of each species to meet this requirement. However, all survey effort between 1988 and the present appears to have identified Asan Bay as fulfilling one or more Ramsar criteria.

And during the Project Surveys in Asan Bay:

  • We recorded an assemblage of globally threatened species each survey visit, including globally Vulnerable Korean Water Deer once; and a total of six species of globally threatened waterbird. Asan Bay therefore continues to fulfill Ramsar Criterion 2.
  • On May 13th 2021, we counted 24,272 waterbirds; and a minimum of 38,999 waterbirds of 51 species, based on the sum of their highest day counts, one per species, between June 2020 and May 2021.  Although no single waterbird species was recorded in a concentration of 20,000 or more individuals, Asan Bay nonetheless continues to meet Criterion 5.
  • We recorded ten species of waterbird in internationally important concentrations of 1% or more of a population, including 10% of the mongolus / stegmanni population of Lesser Sand Plover (“Mongolian Plover”); 3% of the population of Far Eastern Curlew; and >10% of the population of Black-faced Spoonbill.  Most of these species had been recorded in earlier years in Asan Bay internationally important concentrations. Asan Bay continues to fulfill Ramsar Criterion 6.
  • Our count data indicate that all the species of waterbird we recorded are complete migrants. While more research is needed, the number of waterbirds supported during both migration periods, a critical period during these species life-cycles, are likely to far exceed the total number of waterbirds we recorded during only ten dates with survey. Asan Bay continues to fulfill Criterion 4.

Table 1.  Maximum counts of waterbird species made during the Project Surveys (2020-2021) which qualify the species as internationally important or contribute to the international importance of Asan Bay.

 Global Conservation Status (IUCN 2021)1% Threshold (Wetlands International 2021)Max. Count Project SurveysDate of highest countMeets Ramsar Criterion 2Meets Ramsar Criterion 4Meets Ramsar Criterion 6
Common ShelduckLC6002,18129 Mar 2021 xx
Common PochardVU3,0001Jul 21 2021x  
Grey PloverLC1,0001,07229 Mar 2021 xx
Mongolian PloverLC2602,8935 Aug 2020 xx
Far Eastern CurlewEN32091524 Jul 2020xxx
Great KnotEN2,9007,00013 May 2021xxx
Red-necked StintNT3,2004,1705 Aug 2020 xx
DunlinLC10,00011,70029 Mar 2021 xx
Common GreenshankLC1,0002,340Aug 26 2020 xx
Nordmann’s GreenshankEN(5)2Aug 2020, May 2021x  
Black-faced SpoonbillEN(20)479Sep 18 2020xxx
Saunders’s GullVU8514526 Aug 2020xxx

To the best of our knowledge, all four of these criteria are likely to be met “regularly” in Asan Bay, with many birds likely being missed in recent years because of a combination of restricted access and limited survey effort.

Waterbird Use of Asan Bay

During the Project Surveys, as the tide reached > c.7.6m, thousands of shorebirds were watched to fly across from the main tidal area (numbered 1 in Figure 3, and shown below in Figures 4 and 5), where birds were earlier seen to forage, into the three reclamation impoundments.

Figure 4. The main tidal flat in Asan Bay (numbered 1 in Figure 3) during the incoming tide, looking southwest (May 2021) © Nial Moores.
Figure 5. The main tidal flat in Asan Bay during the incoming tide, looking southeast toward the Asan Bay sluice gates (May 2021) © Nial Moores.
Figure 6. May 2021: arrival of shorebirds into the reclamation impoundments (numbered 3 in Figure 3) © Nial Moores

Conditions within each of the three main reclamation impoundments varied substantially each visit during the Project Surveys due to dredging or infilling operations connected to the reclamation process (Figure 7).

Figure 7.  August 2020: piping in of additional mud into the area numbered 2 in Figure 3 © Nial Moores

Each survey, however, the reclamation impoundments provided relatively undisturbed areas of mud or sand above the highwater mark at high tide which were used by roosting shorebirds; extensive shallow lagoon-type areas utilized for foraging and roosting by species like Common Greenshank and Black-tailed Godwit; and areas of open, exposed mud, which were used by up to 4,000 Red-necked Stint in both August 2020 and May 2021 for feeding during both low tide and high tide.

Of potential relevance to discussions about conservation and wise of Asan Bay: in July 2021 we were informed that – for now at least – reclamation work has stopped for an extended period in these reclamation impoundments, presumably to allow new sediment to settle.


Long, A.J., Poole, C. M., Eldridge, M. I. Won P-O & Lee K-S. 1988. A survey of coastal wetlands and shorebirds in South Korea, Spring 1988. Asian Wetland Bureau, Kuala Lumpur.

Ministry of Oceans and Fisheries. 2017. 연안습지 바닷새 보전․관리 연구 『도요‧물떼새 전국 동시조사』(in Korean).

Moores, N. 1999. A survey of the distribution and abundance of shorebirds in South Korea during 1998-1999: an interim summary. Stilt 34: 18-29.

Moores, N. 2012. The distribution, abundance and conservation of avian biodiversity in Yellow Sea habitats in the Republic of Korea. Ph.D. Thesis, University of Newcastle, NSW, Australia.

Moores, N., Rogers, D. I., Rogers, K. & Hansbro, P. 2016. Reclamation of tidal flats and shorebird declines in Saemangeum and elsewhere in the Republic of Korea. Emu, 116, 2: 136-146. Published by CSIRO.

Shorebird Network Korea. 2013. Shorebird population count report of Korea (2011–2012). Shorebird Network Korea Secretariat, Shinan County, Republic of Korea. [In Korean]

Shorebird Network Korea 2014. Shorebird population count report of Korea (2013). Shorebird Network Korea Secretariat, Shinan County, Republic of Korea. [In Korean]

Shorebird Network Korea. 2016. Shorebird population count report of Korea (2014). Shorebird Network Korea Secretariat, Shinan County, Republic of Korea. [In Korean]

Yi, J.-Y. 2004. Status and habitat characteristics of migratory shorebirds in Korea. In ‘Proceedings of the 2004 International Symposium on Migratory Birds, Gunsan, Korea’. pp. 87–103. (Ornithological Society of Korea: Seoul, Republic of Korea). [In Korean]

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