As warming seas push native species to cooler waters farther north, once-rare visitors have become more common<\/p>\n
\u2018It sounds silly but I thought it was a person in the water waving,\u201d says Kurt Lander, skipper of the Yellowfin charter boat, based out of Brighton. But when he grabbed his binoculars, he realised the fluttering movement he had noticed in the middle of the Channel shipping lane was a pair of sunfish.<\/p>\n
The huge fish were lying on their sides and flapping their fins. \u201cApparently, they do it as a visual attraction to birds,\u201d he says. \u201cThey\u2019re trying to get the birds to eat the parasites off them.\u201d<\/p>\n
Lander has seen the huge fish with their unusual round bodies before. But the difference is that those that he spotted this year are part of a surge in sightings of the species off British shores this summer, probably as a result of a marine heatwave.<\/p>\n
Marine heatwaves usually follow long hot spells on land as seas also warm. Last year was labelled \u201cexceptional\u201d by the Met Office, with some parts of British waters seeing heatwave conditions for three-quarters of the year, and 2026 is already showing more of the same.<\/p>\n
The extraordinary temperatures are causing shifts in marine life far beyond an increase in sunfish. Some species are moving away from warmer waters, other \u201cinvaders\u201d are appearing for the first time around Britain\u2019s coastline, while some marine life is dying off under the rays of the sun.<\/p>\n
Lander notices the change in the species of fish he now lands. \u201cI used to catch at least a couple of hundred cod a year,\u201d he says. Now, bringing in cod is rare. If he catches any, he adds, \u201cit\u2019s probably about one or two a year in the summer.\u201d<\/p>\n
Colder water species are just nowhere to be seen off the southern coastline, says Dr Zoe Jacobs, a senior researcher at the National Oceanography Centre in Southampton. Shifting their range to cooler seas farther north, they are now thriving in Scotland. \u201cTemporarily or permanently, we don\u2019t know,\u201d she says.<\/p>\n
Meanwhile, Lander is catching more warm-water fish, such as bass, comber and triggerfish. According to last year\u2019s State of the South-West Seas report, other species found in warmer waters \u2013 such as sardines and anchovies \u2013 are also doing well.<\/p>\n
Gio Reale, a diver based in the Cornish port of Falmouth, says: \u201cSmall water temperature changes have such big effects on marine life.\u201d It has been weeks since he last saw his favourite shark species: the small spotted catshark (also called the lesser-spotted dogfish). These small sharks \u2013 which grow no bigger than a metre and are spattered with delicate freckles \u2013 prefer water temperatures of about 16-17C (61-63F).<\/p>\n
\u201cThis summer, like every day, the water has been about 20C,\u201d he says, adding that he thinks the sharks may have moved into deeper, cooler waters, replicating the way they behave in the Mediterranean.<\/p>\n
These sharks may be missing but common octopuses have arrived in force since January last year, when warmer waters in Devon and Cornwall created perfect conditions for them. This species is native to the UK but not usually seen.<\/p>\n
The bloom caused issues for some crab and lobster fishers. \u201cEveryone\u2019s complaining, \u2018oh, they\u2019re taking all our crabs\u2019,\u201d says Reale. \u201cBut obviously, for the octopus, that\u2019s just a really easy meal. You can just get into a trap where the crabs can\u2019t go anywhere and eat them.\u201d<\/p>\n
Some boats have switched to targeting the now-abundant octopuses, with catches soaring in 2026. The octopuses also provide food for predators, which could explain an increase in sightings of summer visitors such as Risso\u2019s dolphins.<\/p>\n
As sea swimmers know, warmer waters also bring jellyfish \u2013 another food source. But these blooms \u201chave high and low years\u201d, says Jacobs, and interpreting sightings can be tricky: reports may increase simply because more people are at the beach.<\/p>\n