Coastal states claim different widths of sea adjacent to their shores as being subject to their jurisdiction. Claims vary from 3 nautical miles to 200 miles. The purpose of such claims is to reserve for the state in question the right to exploit the economic resources of the area. The different nature of these resources gives rise to related problems of seabed exploitation (usually in relation to the adjacent continental shelf) and fishing rights. This problem is aggravated by the special difficulties of reaching agreement on and determining the exact shore line from which the territorial water limit should be measured (for example, low-tide line or high-tide line), particularly since these change over time. Further difficulties occur in the case of bays, estuaries and inlets, off-shore islands, and straits.
Land-locked countries are placed at a disadvantage if the larger claims are accepted, since this considerably reduces the area falling beyond national jurisdiction and thereby limits access to the resources in the areas encompassed by such claims.
Vessels from the UK, the USA, the USSR, Peru, Japan and many other ocean fishing nations have been charged in recent years with fishing within 200 mile (exclusive economic zones) of other nations. Several of these incidents have included detention or dangerous harassment of vessels and some have been referred to as 'tuna wars'. In 1993 the Chilean navy sought to extend its authority over nearly 8 million square miles of Pacific Ocean extending between its coastline and Easter Island. The Chileans aimed to establish a mar presencial or 'presential sea' for which they would enjoy preferential rights over other nations, with responsibility for fisheries conservation and measures against pollution.
In 1995, hundreds of Chinese fishing boats were reported to be entering Taiwan waters. Such provocations usually draw fire from Taiwan military forces.