The Coast Guard Administration aims to protect the rights of Taiwanese fishermen in the East China Sea.
To achieve this, a temporary enforcement line between Taiwanese and Japanese waters was established in July 2003.
Although some Taiwanese fishing boats have been apprehended within the enforcement line by the Japanese maritime police, the incidence of such cases is decreasing.
The line has thus proven effective.
Japanese and Taiwanese experts, however, still do not agree on how the line should be determined and what legal status it should have.
Japan is a country made up of islands. But because Article 47 of the UN Convention on the Law of the Sea is not beneficial to its territorial sea claims, Japan has chosen in this case not to consider itself as an archipelagic state.
The first clause of Article 47 states: "An archipelagic State may draw straight archipelagic baselines joining the outermost points of the outermost islands and drying reefs of the archipelago provided that within such baselines are included the main islands and an area in which the ratio of the area of the water to the area of the land, including atolls, is between 1 to 1 and 9 to 1."
It is clear that the islands and reefs south of the island of Greater Ryukyu do not meet these proportional requirements and therefore do not justify drawing a baseline as desired.
The UN Convention on the Law of the Sea does not force archipelagic states to claim their rights as stated in the document.
However, allowing such states to define their territorial waters by drawing straight archipelagic baselines that do not follow Article 47 is against the convention's guiding spirit.
Archipelagic states that base their territorial claims on straight archipelagic baselines should be subjected to certain restrictions. This has been overlooked in the convention.
If Japan -- in addition to its 200 nautical mile (370.4km) exclusive economic zone and continental shelf rights -- is allowed to use straight archipelagic baselines, using the Miyako and the Yaeyama Islands -- including Ishigaki, Iriomote and the Yonaguni islands, which are closer to Taiwan than Japan -- Japan will clearly be infringing on Taiwan's territorial waters.
Japan's territorial water claims violate four articles in the UN convention.
Article 15 deals with delimitation of the territorial sea between states with opposite or adjacent coasts. Article 74 deals with the delimitation of the exclusive economic zone between states with opposite or adjacent coasts. Article 83 deals with the delimitation of the continental shelf between states with opposite or adjacent coasts.
Japan is also violating Clause 6 of Article 7, which states: "The system of straight baselines may not be applied by a State in such a manner as to cut off the territorial sea of another State from the high seas or an exclusive economic zone."
In other words, Japan cannot draw a straight archipelagic baseline between the Yaeyama and Miyako Islands since that would cut off Taiwan's territorial waters and exclusive economic zone.
In June 1996, Japan announced straight line base points as well as baselines.
The southernmost base point, point 66, is located on the southern tip of Greater Ryukyu Island at 26 degrees 4 minutes and 30 seconds north and 127 degrees, 39 minutes and 25 seconds south.
Japan has not announced any base points or baselines on the Miyako and Yaeyama islands, but is probably considering doing so.
Japan cannot use these islands to back a claim for an exclusive economic zone or continental shelf rights.
There are a number of reasons for this.
The islands are located further than 185.2km away from the Greater Ryukyu Islands, and even further away from the island of Kyushu. The regulated length of a baseline is 185.2km. These islands are in fact located closer to Taiwan.
The surface area of the islands is also too small.
The area of the Yaeyama Islands is 591.8km2 and the area of the Miyako Islands is 225.86 km2. These islands do not entitle Japan to a 370.4km exclusive economic zone because if a middle line is drawn between the islands and Taiwan it infringes upon the equity principle.
Yonaguni Island in particular only has a surface area of 28.88km2.
In addition, the waters between the Yaeyama and Miyako islands and Greater Ryukyu Island fall within the scope of Taiwan's 370.4km exclusive economic zone.
An exclusive economic zone can therefore not be given based on the Yaeyama and Miyako island groups without disrupting the continuity of Taiwan's territorial waters and exclusive economic zone.
The island groups should, however, be entitled to the 22.2km territorial waters.
In addition, the waters surrounding the Yaeyama, Miyako and Greater Ryukyu islands are the traditional fishing waters of Taiwanese fishermen.
Based on article 51 in the UN convention, which deals with existing agreements, traditional fishing rights and existing submarine cables, Japan should take into account the traditional fishing waters of Taiwanese fishermen.
The greater issue surrounding the temporary enforcement line is the northern line drawn from the Diaoyutai, or Senkaku, islands. If Japan doubts the legitimacy of this line, negotiations could be held to define a jointly managed fishing area.
Chen Hurng-yu is a professor at the Graduate Institute of Southeast Asian Studies at Tamkang University.
Translated by Perry Svensson
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