Giant sunfish numbers increase in Irish waters as temperatures rise

17 Jan 2022

New research from UCC has found that warming seas have caused the giant sunfish to venture north into Irish waters. The discovery comes after almost 50 years of observations off the Cork coast.

A study by a team of researchers from Ireland and the UK including Dr Tom Doyle, School of Biological, Earth and Environmental Sciences, UCC, has found that ocean sunfish, the largest bony fish in the world, have expanded their range in the 1990s and 2000s by more than 200km north.

The study was published in the international peer-reviewed journal Marine Biology, and analysed sightings of sunfish made from the Cape Clear coastal bird observatory by thousands of experienced bird watchers over 4,600 days of sea watching.

Senior study author, Dr Tom Doyle commented:

“For a long time now we have suspected that sunfish have increased in Irish waters, but it is only now, after retrospectively analysing 47 years of coastal sightings from the Cape Clear bird observatory, that we can say for sure that sunfish increased in the 1990s and 2000s”. 

The sunfish is very recognisable because of its unusual flattened shape and size. Measuring up to 3.2m long and weighing as much as 2.3 tonnes, they are found in all temperate and tropical waters and seasonally migrate to warmer waters. As adults, they feed almost exclusively on jellyfish.

They are excellent swimmers, capable of long-distance migrations and deep dives, and they are easily spotted when they swim on their side at the ocean’s surface, known as "basking".

Steve Wing, the head warden at Birdwatch Ireland’s Cape Clear bird observatory, said the study has demonstrated how sustained citizen science projects can provide unique insights on the historical abundance of enigmatic species.

Source: Irish Examiner. Read the full article here