An archipelago of avian life
Dadohaehaesang National Park, established in 1981, is the largest national park in South Korea, covering 2,321.5 square kilometers. The vast majority of this area is marine territory, encompassing over 1,700 islands and rocky outcrops scattered across the Yellow Sea. This "sea of many islands" provides nesting grounds for at least 147 bird species, making it one of East Asia's most significant avian breeding areas.
Two islands in particular, Gugul-do and Chilbal-do, are designated as Natural Monuments due to their immense biological value. These remote, rocky islands host enormous breeding colonies of several important seabird species. The most numerous resident is the black-tailed gull (Larus crassirostris), a medium-sized gull with a distinctive, cat-like call. Tens of thousands of these gulls arrive each spring, with breeding initiated in early April. The park is also an important breeding site for the near-threatened Swinhoe's storm petrel (Hydrobates monorhis). An estimated 100,000 pairs nest on Gugul-do island, a figure that may represent more than 75% of the entire global population for the species. Other significant breeding species include the streaked shearwater (Calonectris leucomelas) and the ancient murrelet (Synthliboramphus antiquus).
Counting birds to measure the sea
The seabird colonies of Dadohaehaesang are a wildlife spectacle; they are a, living measure of the Yellow Sea's health. The population dynamics of species like the black-tailed gull are closely linked to the availability of their primary food sources—small fish, mollusks, and crustaceans. Overfishing of commercially important species such as the small yellow croaker and hairtail has depleted fish stocks throughout the Yellow Sea. This pressure, combined with pollution from industrial and domestic waste, directly impacts the food web that the seabirds depend on.
Researchers monitor the breeding success and population sizes of the colonies to gauge these changes. A successful breeding season, with high numbers of fledged chicks, generally indicates healthy and abundant fish stocks in the surrounding waters. Conversely, a poor season with high chick mortality can signal a decline in marine resources. For this reason, long-term monitoring of the seabird populations is an important conservation strategy. The data provides an early warning system for the broader marine ecosystem, reflecting the consequences of overfishing and environmental pollution that affect the more than 600 million people living in the Yellow Sea watershed.