Importance, threats and conservation status
Wetlands International, 2002
ISBN 90 5882 009 2
6. Threats to shorebirds
Approximately 600 million people (about 10% of the world's population) live in the river catchments draining into the Yellow Sea (UNDP 2000a). The Yellow Sea coastal provinces support 20% of the 1 400 million Chinese population and 53% of the 46 million South Korean population. Large coastal cities with more than two million inhabitants include Dalian, Tianjin, Qingdao, Rizhao, Shanghai, Seoul-Incheon and Pyongyang-Nampo (Yuan et al. 2001; UNDP 2000a).
The rapid growth of the populations and economies of China and South Korea is causing serious environmental problems for the Yellow Sea through loss and degradation of coastal habitats. The major causes of shorebird habitat loss are reclamation for industrial development, agricultural land, salt works, housing, mariculture and fresh water reservoirs. Degradation occurs due to pollution from industrial, agricultural and domestic sources, and unsustainable fishing (UNDP 2000a; Anon 1998b).
The major environmental issues in the Yellow Sea have been identified as (UNDP 2000a):
- degradation of biodiversity, and loss of coastal habitats, including fish spawning and nursery grounds and migratory bird habitat;
- water quality deterioration;
- human health problems, caused by airborne pollution and water-borne dispersion of contaminants and pathogens;
- decline of commercial fisheries;
- unsustainable mariculture;
- harmful algal blooms.
A summary of the size and scope of threats to the Yellow Sea is presented below.
Approximately 37% of the intertidal areas existing in the Chinese portion of the Yellow Sea in 1950 and 43% of those in the South Korean part in 1917 have been reclaimed to date (Yuan et al. 2001; Moores et al. 2001; MOMAF 1998). In North Korea, reclamation of intertidal areas for food production has been a national priority for many years and, during the last decade, more than 700 km2 has been reclaimed in one province alone. Massive reclamation projects have also been undertaken in other coastal areas, indicating that loss of intertidal areas in North Korea is occurring at a high rate (UNDP 2000c).
Extensive reclamation is ongoing (pers. obs.) and China has plans to reclaim a further 45% of its existing Yellow Sea mudflats (Yuan et al. 2001) and South Korea, 34% (Moores et al. 2001). Although there has been serious questioning in South Korea of the environmental consequences resulting from reclamation (Anon 1998b), the Saemangeum Reclamation Project, which at 401 km2 is probably the largest reclamation activity in the world, was restarted in 2001 after a moratorium period. This project will destroy the two most important shorebird areas in South Korea (the Mangyeung and Dongjin estuaries).
In North Korea, it is believed that the substantial investments that have already been made in seawalls and irrigation channels will ensure that wetland habitat will continue to be lost (UNDP 2000c).
The two longest rivers in China, the Huang He and Chang Jiang, are undergoing significant changes that will greatly reduce the amount of sediment being transported into the Yellow Sea. This will seriously affect their ability to nourish intertidal flats through supply of fresh silt and nutrients.
Until 1990, the 5 000 km2 Huang He Delta increased in area annually by about 32 km2 and grew outwards by 2 km (Yuan et al. 2001). However, in recent years the situation has changed dramatically due to increased water extraction from the river for agricultural, industrial and domestic purposes. The average duration of non-flow in the lower reaches of the river has increased from 14 days in the 1970s to 102 days in the 1990s. In 1997, the Huang He ceased flowing at the mouth for 226 days. During the period 2010-2019, water and sediment flows are predicted to decline by 34% and 49%, respectively, from the levels in the 1980s (YRCC 2000). The large reductions in water and sediment flows to date have already seriously affected the ecosystems of the Yellow River mouth, through reduced nutrient inflows, increased concentration on pollutants, salt water ingress and erosion, leading to reduced biological productivity (ADB 2000b). Modifications to sedimentation processes can also cause detrimental changes in the benthic fauna community (Paton 2000).
The commissioning of the Three Gorges Dam in the middle reaches of the Chang Jiang (partly by late 2003, completely by 2009) is predicted to reduce sediment discharge to the sea by 11% (Zhu 1987 in Yang 1999b). Yang (1999b) predicts that about 200 km2, or about 22%, of the Chang Jiang's intertidal flats will be lost due to erosion within the next 100 years. This loss will be exacerbated by the plan to overcome increasing water shortages in northern China by transferring 48 x 109 m3 of water annually from the Chang Jiang northward, via three channels, to the Huai He and Huang He.
Numerous smaller rivers flowing into the Yellow Sea are also being affected in similar ways leading to reduced sediment input to coastal areas, which often results in erosion of estuaries and intertidal areas (Yuan et al. 2001).
The rate at which new intertidal areas will be created in the future is likely to decline significantly as a consequence of the greatly reduced sediment input to the Yellow Sea. Therefore, whereas in the past ongoing accretion was able to partly replace reclaimed intertidal areas its ability to do so in the future will be greatly diminished. Thus, it can be predicted that the rate of decrease in intertidal area will accelerate.
The major pollutants in the Yellow Sea are oil, inorganic phosphorous, inorganic nitrogen and heavy metals (Yuan et al. 2001; Moores et al. 2001). Long-term monitoring in China shows that seawater quality is steadily deteriorating (Yuan et al. 2001).
In the Bo Hai, 2 990 million tonnes of industrial effluent and domestic sewage are discharged annually, representing 34% of the total national marine discharge (ADB 2000b) despite the Bo Hai being only 1.6% of the total Chinese sea area. Additionally, more than 100 million tonnes of domestic sewage and about 530 million tonnes of industrial waste water are discharged annually into near shore areas of the central western Yellow Sea (UNDP 2000a) and approximately 600 million tonnes per year of waste water into the west and south coastal areas of South Korea (Moores et al. 2001).
It is considered that Jinzhou Bay, an internationally important area for shorebirds in northern Liaodong Wan, has the highest heavy metal pollution levels in the world (ADB 2000b). In 1999, 25% of the sampling stations in the Bo Hai had average oil pollution levels above the Chinese national standard of 0.05 mg L-1 maximum (ADB 2000b). Monitoring at more than 80 sites on the Chinese coast showed that 50% of shellfish had unacceptably high levels of harmful pollutants, with the main ones being oil, chromium, arsenic and DDT (Yuan et al. 2001). The incidence of algal red tides is increasing with 14 having been recorded in 1998 along the west coast of the Yellow Sea (Yuan et al. 2001) and 19 on the eastern side (Moores et al. 2001).
It is estimated that 100% of fish spawning and nursery sites (i.e. intertidal areas) in the Bo Hai and 70% in the central west Yellow Sea are suffering from serious pollution and lack of river runoff and this is resulting in a sharp decrease in finfish and shellfish biomass (Yuan et al. 2001). The reduction in intertidal shellfish numbers is also well documented for South Korea (Koh 1997).
The traditional dependence of coastal communities around the Yellow Sea on wetland food resources has meant that people have always been using the intertidal areas, either directly for food or to gain access to fishing boats moored at the water's edge. In recent years greatly increased human population numbers have led to unsustainable harvesting of shellfish and potentially serious human disturbance of shorebirds (pers. obs.), even in Protected Areas. The move to mechanical shellfishing (pers. obs.) can be expected to exacerbate the problem by increasing shellfish removal rates and reducing shellfish productivity over the long term through severe disturbance of sediments (Piersma et al. 2001).
Human disturbance not only occurs on the feeding areas but also in the shrimp and fish ponds, and saltpans, which are often the only available roosting areas for shorebirds at high tide when the natural roosting areas on the intertidal flats have been destroyed by reclamation.
Disturbance from oil exploration, drilling and extraction activities can be serious. There are four large oil fields in the Bo Hai, which accounted for 24% of national production in 1996 (ADB 2000b). Internationally important shorebird areas that contain oil fields are Huang He NNR, Tianjin Municipality, Linghekou and Shuangtaizihekou NNR.
There have been a number of investigations into hunting activity in the Chang Jiang Estuary (Tang & Wang 1991, 1992, 1995; Barter et al. 1997c; Ma et al. 1998). Tang and Wang (1992) estimated that approximately 30 000 and 9 000 shorebirds were captured with clap nets in the 1991 and 1992 northward migrations, respectively. They suggested that the decrease between the two years could be due to declining hunter numbers, increasing incomes from alternative activities and/or reduction in shorebird habitat due to reclamation. However, a study during the 1996 northward migration showed that hunter numbers had not declined since 1991 and that the number of shorebirds caught was similar (Barter et al. 1997c). More recent studies (during the 2000-2001 period) indicate that hunting activity has now declined at Chongming Dao (Ma et al. 2002; T.H. Wang in litt.).
Wang et al. (1991, 1992) reported hunting activity in the Huang He Delta in the 1991 southward and 1992 northward migrations and it was estimated that 18 000-20 000 shorebirds were caught with clap nets during northward migration and probably a higher number during southward migration. However, no hunting was observed in the Delta during surveys in the 1997, 1998 and 1999 northward migrations.
With the exception of the Chang Jiang Estuary, no hunting activity has been detected in China during recent shorebird surveys that covered about one-third of the Chinese intertidal areas between 1996 and 2001 (pers. obs.).
The situation appears to be similar in South Korea (N. Moores in litt.), with the only reported instance being minor hunting activity in Mangyeung Gang Hagu (J.H. Kim pers. comm.).
Thus, hunting appears to be a minor threat to shorebirds using the Yellow Sea, with the exception of in the Chang Jiang Estuary where the activity is reportedly declining.
In order to survive and migrate successfully, shorebirds must have access to suitable feeding areas and roosting sites.
Healthy intertidal flats are essential for the spawning, growth and survival of the benthic fauna on which shorebirds feed, e.g. shellfish, crustaceans, crabs and worms. The amount and quality of these areas are being very seriously threatened by reclamation, reduced river flows, pollution, human disturbance and unsustainable harvesting of benthic fauna.
The significant amount of reclamation that has occurred to date in the Yellow Sea has directly affected shorebirds by greatly reducing their feeding habitat and, in many cases, the availability of roosting areas. It is predicted that the situation will get worse in the future as intertidal areas are lost at an increasing rate due to the combined effects of reclamation and reduced accretion. These effects will be exacerbated by the predicted rise in sea level.
Declining river flows are leading to decreased benthic productivity and, probably, changes in the benthic fauna community, which is also being affected by massive pollution from many sources. Changes in sedimentation processes may detrimentally affect the nature of the benthic community. Reduced availability of food will adversely affect the ability of the Yellow Sea intertidal areas to support the very large numbers of shorebirds that are dependent on them to successfully complete their annual migrations.
Human disturbance can also affect feeding and roosting birds by reducing feeding time and causing them to fly and use energy resources unnecessarily.
Serious depletion of benthic fauna due to unsustainable harvesting can be expected to negatively affect shorebirds through removal of an important shorebird food source. Mechanical harvesting will make the situation worse through serious disturbance of sediments, which adversely affects long term benthic productivity.
Shorebirds have to meet a very tight schedule on the breeding grounds, needing to complete the breeding process during the short summer so that they and the young birds can leave before the weather deteriorates. The schedule requires that birds arrive on time and in good breeding condition. Therefore, the adverse effects of the various threats being encountered in the Yellow Sea are most significant during northward migration when shorebirds are not only putting on fuel stores (mostly fat) for their long flight into the breeding grounds, but also additional reserves to sustain them during the period immediately after arrival when feeding conditions may be poor.