What davejb said. Fisheries, pollution and such other coastal patrol functions are the responsibility of other agencies.
The Nimrod was an ASW and ASUW (old speak) military platform, which also carried out a multitude of other essential military tasks. The SAR and fisheries stuff was very much ancillary tasking which was performed, when requested, if the aircraft were not busy doing their actual job, which was defending the country or training to do so.
Pretty picture though.
