Key Terms
20.There are a number of existing terms which are used throughout the Act to describe the area to which it applies. These are set out below.
Baseline
The marine area is measured from a “baseline”.  This is usually the low water mark around the coast.  However, there may be straight baselines around the mouths of bays, and all rocks and reefs above the sea at low water but submerged at other times extend the baselines if they are within 12 nautical miles of the mainland or an island.  The UK baseline is delineated in the Territorial Waters Order in Council 1964 (as amended by the Territorial Sea (Amendment) Order 1998, SI 1998/2564).
Territorial Sea
The UK territorial sea is defined by the Territorial Sea Act 1987 as the sea extending 12 nautical miles from the baseline.  The UK territorial sea is divided into areas which form parts of Scotland, Wales and Northern Ireland for the purpose of exercising devolved functions.  Northern Ireland is defined in section 98 of the Northern Ireland Act 1998 as including so much of the internal waters (those landward of the baseline) and the territorial sea of the United Kingdom as are adjacent to Northern Ireland.
British Fishery Limits
British fishery limits currently extend 200 nautical miles from the baseline.  As with the territorial sea, Scotland and Northern Ireland have their own areas within British fishery limits.  In the case of Northern Ireland this area (which includes the territorial sea) is defined in the Adjacent Waters Boundaries (Northern Ireland) Order 2002 and is known as the Northern Ireland zone.
The Marine and Coastal Access Act 2009 provided for equivalent arrangements for Wales through the designation of a Welsh zone for fisheries matters by an Order in Council.