Wetlands - Korea's most-threatened habitat: 1

by Nial Moores, from OBC Bulletin 36, December 2002.

South Korea lacks endemic bird species, and is rather poor in terms of avian dry land diversity compared with other East Asian countries, but its wetlands and waterways are extremely important for the future conservation of migratory waterbird species, around 13 of which are globally threatened, and for the future well-being of the human population. Its extensive tidal-flats support three charismatic and threatened near-endemic breeding species (Saunders's Gull Larus saundersi, Chinese Egret Egretta eulophotes, and Black-faced Spoonbill Platelea minor) and a very significant percentage of the East Asian Australasian Flyways shorebirds. Rivers, reclamation lakes and rice-fields support more than 1 million migrant and overwintering waterbirds, including most of the world's Baikal Teal Anas formosa, White-naped Grus vipio and Hooded Cranes Grus monacha.

Chinese Egret
(Morten Strange)

Amongst East Asian countries it has one of the richest economies and one of the strongest environmental movements too, boding well for long-term conservation. Yet, presumably as it lacks an international NGO and has not yet received much interest from foreign birders, South Korea still remains something of a relative unknown to the worlds conservation and birding communities. This article therefore aims to highlight the importance of Koreas wetlands for migratory bird populations, and give additional information on threats and conservation initiatives.

Geography and Climate
South Korea forms the southern part of the north-south oriented Korean peninsula, lying broadly between 34 and 38 degrees North, and between 126 and 130 degrees East. It is surrounded by sea on three sides, with the Yellow Sea to the west (bordered by China, North Korea and South Korea, this semi-enclosed shallow sea has an average depth across the whole of only 44 m), the South Sea or Tsushima Strait to the south, and the deep East Sea (or Sea of Japan) to the east. Due to these seas ameliorating effects, South Korea has elements of both continental and maritime-temperate climates.

Winters are generally dry and cold with periods of prolonged subzero temperatures in the north, especially away from the coast, but often milder, wetter conditions in the south, leading to inland rivers freezing in the north but largely unfrozen tidal-flats and coastal reclamation lakes in the southwest and southeast (determining the mid-winter distribution of species such as Saunders's Gull and Baikal Teal). Summers are generally hot and humid (with daily maxima typically above 30°C in the warmest areas), and the heaviest rains usually fall between June and September, either as part of summer monsoons or carried by typhoons. Drought conditions are reasonably frequent, further stretching very limited water resources.

Wetlands
There are two broad categories of wetland supporting significant concentrations of waterbird in South Korea and the food needs of much of the human population: intertidal/tidal and freshwater. Both should be considered global conservation priorities. As of 1998, tidal-flats covered approximately 280,000 ha (with most unvegetated, and only small areas supporting Suaeda saltmarsh), while the six major flood-plain/coastal plain areas nationwide (five in the west, one in the southeast) now contain most of the freshwater waterbird habitat.

Intertidal Wetlands
Due to differences in coastal slope and tidal-ranges, intertidal wetlands are not distributed evenly around the coast, and approximately 83% of tidal-flats are found along the west coast, with 17% along the south coast. Most major rivers (including the Geum in the west, the Yeongsan in the southwest and the Nakdong in the southeast) have been barraged at their estuaries since the late 1980s, effectively removing the brackish estuarine zone (the clear preference of Black-faced Spoonbills and several species of shorebird), with only the Han now providing substantial brackish and freshwater tidal zones. Here, despite the proximity of Seoul, such habitat still supports small numbers of wintering White-naped Cranes and up to 1,500 Swan Geese Anser cygnoides, especially during migration. In addition, almost all tidal-flats nationwide have extensively developed hinterlands and most are used for intensive shellfish harvesting, further limiting waterbird use. No intertidal areas (at the time of writing) are comprehensively protected or managed for wildlife.

White-naped Crane
and Hooded Crane
(Pete Morris/Birdquest)

Along the mainly rocky and sand beach east coast, the tidal range reaches only 0.3 m, and with the exception of northeastern coastal lagoons that support 2030 over-wintering Mute Swans Cynus olor, there are relatively few waterbirds of international importance. The tidal range, however, increases gradually along the south coast, from an average 1 m in the Nakdong estuary in the far southeast to 5 m during spring tides in Mokpo in the southwest, and northward into the Yellow Sea, where it peaks at 910 m (one of the worlds highest tidal ranges) in the vast Gyeonggi Bay in the northwest. As a result of this tidal range combined with a shallow coastal gradient and heavy sediment deposition (by Korean rivers and also by the Yellow and Yangtze rivers across the other side of the Yellow Sea) extensive and wide tidal-flats stretch southward from Gyeonggi Bay along much of the west coast and in bays and small estuaries along the south coast. Mud and silt flats tend to predominate in the north (preferred by species such as Eastern Curlew Numenius madagascariensis, with several thousand staging in Gyeongi Bay) while sandier sediments become more typical in the southwest.

Remote islands adjacent to Seoul and Incheon cities, especially those near the Demilitarized Zone (or DMZ), are used as breeding sites for most of the worlds remaining populations of Chinese Egret, Black-faced Spoonbill and the distinctive Eastern Oystercatcher Haematopus (ostralegus) osculans. The same islands are also used by nesting Black-tailed Gulls Larus crassirostris and local Yellow-legged Gulls, invariably pink-legged, and perhaps better called Mongolian (or Korean?) Gulls Larus (cachinnans) mongolicus. At least three temporary Saunders's Gulls colonies have also been found (the first in 1998) in young salt-marsh growing up in embanked areas prior to landfill, at Shiwa, Song Do and Yeongjong. Subzero temperatures in winter can leave foreshores frozen, though sea temperatures remain several degrees above freezing and a range of species remain, including small numbers of Red-Crowned Cranes Grus japonensis on tidal flats at Ganghwa and Yeong Jong. In the extremely cold winter of 2001 a single flock of 143 Relict Gulls Larus relictus was found at Song Do in Incheon, with several smaller flocks elsewhere, presumably having moved southward from even colder northern parts of the Yellow Sea. This count, combined with high Relict Gull counts in autumn from Happy Island, Hebei Province and November counts elsewhere in the northern Yellow Sea (Paul Holt in litt.), strongly suggest that the tidal-flats of the Yellow Sea form the core of this enigmatic gulls winter distribution.

| Korea wetlands: 2 |