I am advised by the Department of Foreign Affairs and Trade that the position is as follows.
The exclusive economic zone (EEZ) is the body of water that stretches from 12 nautical miles offshore out to a distance of 200 miles. The seabed beneath the EEZ is the continental shelf.
Largely due to efforts made by Ireland throughout the 1970s, international law is now clear that uninhabitable rocks such as Rockall have no entitlement to a continental shelf or an EEZ and so, sovereignty over such a rock is irrelevant for the purposes of establishing boundaries between continental shelves and EEZs of neighbouring States. Sovereignty, and whether such a rock has a 12-mile territorial sea, are separate issues that do not arise in establishing boundaries between continental shelves and EEZs.
The 2013 Agreement built on the 1988 Agreement between Ireland and the UK that had already established continental shelf boundaries and provides that those boundaries, slightly adjusted to ensure that no waters were lost to the high seas, shall also be the EEZ boundaries. This created a single maritime boundary between 12 and 200 miles in the water and on the seabed beneath.
As you are aware, Ireland has never made any claims to Rockall nor have we recognised British claims to sovereignty over it. Nothing in either Agreement altered that position or represented a departure from our long held view, nor does either Agreement have any implications for the present difficulties between Ireland and Scotland over fishing rights around Rockall.
As regards the situation following Brexit, the Irish and EU position, as set out in the March 2018 European Council Guidelines for negotiations on the future relationship, is that existing reciprocal access to fishing waters and resources should be maintained.
The main purpose of the 2013 Agreement was to resolve jurisdictional uncertainty. It addressed the situation of fishing vessels seeking to avoid inspection in Irish EEZ areas that overlapped with the UK-claimed areas. The issue of Rockall did not arise in the 2013 Agreement as it was not relevant. Importantly, however, it also provides the legal certainty necessary for raising finance to develop renewable energy projects in the areas concerned and it resolved confusion over responsibility for dealing with marine pollution incidents in those areas.