Scientists warn rare octopus blooms could become common in UK waters

Octopuses are becoming an increasingly familiar presence in British waters after a dramatic population surge recorded in 2025, according to marine scientists.

Research by the Marine Biological Association (MBA) found that rising sea temperatures have encouraged the common octopus to expand its range northwards from southern Europe, with large numbers now appearing along the south-west coast of England.

The study links the influx to unusually warm conditions in the English Channel, with sea temperatures last year reaching up to 4C above average — levels described by researchers as highly favourable for octopus breeding and survival.

While scientists say the shift offers new insight into how marine species are responding to climate change, parts of the fishing industry have raised concerns about the impact on shellfish stocks. Octopuses are known to prey heavily on crabs, lobsters and scallops, all of which are key species for coastal fishing communities.

The MBA report describes 2025 as a year of “major population bloom”, comparable to rare historical events recorded at the turn of the 20th century and in the mid-1900s. Commercial landings of common octopus in south-west England were almost 65 times higher than recent annual averages.

Researchers analysed catch data from fisheries alongside scientific surveys, with funding from the Department for Environment, Food and Rural Affairs (Defra), Plymouth City Council and Devon County Council.

The common octopus can grow up to a metre in length and is a highly adaptable predator. Scientists say its populations fluctuate sharply depending on environmental conditions, including temperature, salinity and ocean currents.

Lower salinity levels and persistent easterly winds during 2025 are thought to have helped newly hatched octopuses drift from northern France and the Channel Islands into UK waters. Modelling also suggests larvae from Guernsey — which experienced its own octopus surge in 2024 — may have contributed to the increase.

Dr Bryce Stewart of the MBA said the species may now be establishing itself more permanently in British seas. “It was always present, but in very low numbers,” he said. “What we’re seeing now suggests it could become genuinely common.”

For many fishers, the change has been disruptive. A survey of 40 fishermen found that around two-thirds reported negative effects, particularly those dependent on crab, lobster and scallop fisheries. Data from the Marine Management Organisation show catch rates for these species have fallen by between 30% and 50%.

Some operators have adapted by investing in octopus fishing gear, with the species fetching prices of around £7 per kilo.

However, others fear long-term damage to shellfish stocks and uncertainty over whether the octopus boom will persist.

Alan Steer, a third-generation crab fisherman from South Devon, said last year’s surge allowed some short-term gains but created wider problems. “We rely on strong crab catches through the winter to get us to spring, and those numbers just haven’t been there,” he said.

He added that switching to octopus fishing would require costly investment and carried risks if populations fall again in future years.

Defra said the research provided an important foundation for understanding the changing dynamics of UK seas. A spokesperson said the department was working with the fishing industry through fisheries management plans to promote sustainability, alongside a £360m Fishing and Coastal Growth Fund aimed at supporting coastal communities.

Scientists warn that further octopus blooms are possible if warm conditions in the Channel continue, highlighting how climate-driven changes are reshaping marine ecosystems around the UK.