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Marine heatwaves reshape British seas

scienceAug 17, 202614214

Skipper Kurt Lander of the Yellowfin charter boat off Brighton reported an unusual surge of sunfish this summer, part of a broader rise in warm-water visitors linked to marine heatwaves. The Met Office called last year’s conditions exceptional, with some British waters experiencing heatwave conditions for three-quarters of the year, and 2026 showing similarly high temperatures. Fishers such as Lander say formerly common cod have become rare, with one or two caught in summer now instead of hundreds, while warm-water species including bass, comber, triggerfish, sardines and anchovies are doing well, according to the State of the South-West Seas report. Dr Zoe Jacobs of the National Oceanography Centre in Southampton says colder-water species have shifted north and are thriving in Scotland, though it is unclear whether those range shifts are temporary or permanent. Diver Gio Reale in Falmouth reported the small spotted catshark has largely disappeared from shallow waters this summer as sea temperatures hover around 20C rather than the species’ preferred 16, 17C. Warmer conditions since January last year produced a boom in common octopuses in Devon and Cornwall, prompting some boats to switch to targeting octopus and producing soaring catches in 2026, while crab and lobster fishers report increased predation. These changes are already reshaping local fisheries and marine food webs and are producing uncertain, possibly long-term redistributions of species around British coasts.

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