It is thought it may have been lured by plankton which had bloomed early in the lough because of the warm weather.
 

The species is the second biggest fish in the world - growing up to 43ft (13m) in length.
 

Monday's sighting came just a day after the first basking shark of the year was spotted in Irish waters between Lambay Island and Rockabill off the north Dublin coast by a member of the Irish Whale and Dolphin Group.
 

Extremely unusual
 

Dr Graham Savidge, reader in marine biology at Queen's University, said: "We were taking students out on their annual field trip to sample water in the Coyle estuary when the research technician spotted the shark's fins.
 

"We were about 100m (328ft) away but by judging the distance between the dorsal and caudal fins gliding through the water we were able to roughly calculate its length.
 

"We didn't approach too closely because we didn't want to disturb the shark."
 

According to Dr Savidge, the sighting of the shark is extremely unusual for this time of year as there are only a few sightings in the lough each year and these are usually in the high summer months of July and August.
 

However, in recent years there has been a rise in the number of sightings of the coast off the British Isles which is believed to be partially due to climate change as the sharks follow plankton from warmer seas.
 

But, despite the increasing number of sightings which could, in fact, just be a rise in the number of people spotting the same creature, the sharks are regarded as an endangered species.
 

In the Far East their huge fins - which grow up to 2m (6ft 5ins) in length - are regarded as a delicacy.