Ocean sunfish sightings are reported around the British Isles from time to time, but if you always reckoned that your best chance of diving with the world’s largest bony fish would require a trip to the Far East, you might just get lucky closer to home.
It turns out that Mola mola can be found in Irish waters year round – and in far higher numbers than was previously thought.
The new insights come from scientists at University College Cork’s School of Biological, Earth & Environmental Science and the MaREI Centre for Marine and Renewable Energy, collaborating with researchers in Spain and the Netherlands.
It’s known that ocean sunfish grow as long as 3m and can weigh up to a tonne, but their migratory patterns have remained relatively mysterious. They were known to visit Irish offshore waters in summer to feed off jellyfish blooms, but it was long presumed that they would move south to warmer waters in autumn.
The team carried out year-long aerial surveys of Irish offshore waters, flying more than 10,500 miles in summer and winter and extending almost 200 miles into the Atlantic. Their ObSERVE Aerial project was said to be the first comprehensive offshore survey effort in good weather during winter.
The researchers’ findings confounded the previous belief that sunfish were relatively rare visitors, as it was estimated that at least 12,700 could be found offshore in summer – with a minimum of 8200 remaining even in winter.
“Because sunfish spend upwards of 80% of their time below the surface where we can’t see them, both summer and winter estimates represent minimum estimates,” said lead author of the study Dr Patricia Breen.
“The data we have collected will be important to determine the numbers and distribution of many protected marine species during the winter period.”
The study identified several key areas of high sunfish density, thought to reflect jellyfish distribution, and estimated that the sunfish consumed around 2600 tonnes of jellyfish a day to maintain their great bulk.
“This makes sunfish an incredibly important part of the marine eco-system,” said marine ecologist and team-member Dr Mark Jessopp. “They are likely to play a largely unrecognised but important role in controlling large jellyfish blooms.”
New Insights into Ocean Sunfish (Mola mola) Abundance and Seasonal Distribution in the Northeast Atlantic is published in Scientific Reports and can be read here
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12-Jul-17
