Since early 2025, common octopus, Octopus vulgaris, has turned up off the coasts of Devon and Cornwall in numbers nobody currently fishing those waters has seen before. By the end of the summer, UK fishermen had landed more than 1,200 tonnes of the animal in a single season, according to reporting on the bloom’s scale. A report published in January 2026 by the Marine Biological Association, Plymouth Marine Laboratory, and the University of Plymouth found that this is only the fourth event of its kind recorded in the past 125 years, and the largest of the four.
The report, funded by Defra along with Plymouth City Council and Devon County Council, identified three earlier blooms in the historical record: 1899 to 1900, 1932 to 1933, and 1950 to 1951. Each was followed by a long gap with no comparable event. The current bloom, which began accelerating through 2025 and was still being monitored into 2026, is described in the report as at least as extensive as any of the three that preceded it, and by some measures the largest seen in the region for at least 75 years.
What the report’s authors actually measured
The research team, which included Dr Bryce Stewart of the Marine Biological Association and the University of Plymouth, Professor Tim Smyth of Plymouth Marine Laboratory, and Professor Emma Sheehan of the University of Plymouth, combined landings data, sea temperature records, and surveys of working fishermen to build a picture of both scale and cause. Warmer than average sea temperatures, both during the bloom years and in the year preceding each one, showed up as the one consistent factor across all four historical events. Sustained easterly winds were identified as the likely mechanism carrying octopus larvae from spawning grounds around the Channel Islands and northern France into UK waters, and current modelling in the report supports the idea that larvae from a bloom already under way off Guernsey since 2024 contributed to what followed in the South West.
None of this establishes a single cause with certainty. The report describes warm water and wind driven larval transport as the two strongest correlates in the data available, not as a settled mechanism. Blooms this rare, occurring four times in over a century, do not offer enough repeat events for that kind of confidence.
What it has done to other fisheries
Octopus is a voracious, opportunistic predator, and its sudden abundance has had a measurable effect on the animals that share its habitat. The report found that catch rates for brown crab, lobster, and scallops fell by between 30 and 50 per cent in 2025 compared with recent years, and more than half of the 40 working fishermen surveyed for the report reported negative impacts, mainly attributed to octopus predation on pots and gear as well as on the target species themselves.
Brian Tapper, a Plymouth crab fisherman with 39 years on the water, described the shift to ITV News West Country in stark terms: “We used to have a tonne of crab a day but have not had a tonne all year… The octopus eat everything in sight, they are like locusts.” Cllr Tudor Evans of Plymouth City Council called the bloom “a sustained threat” rather than a short term disruption, a framing the report’s continuation into 2026 appears to support.
Do not read this as good news for the fishing industry overall
Octopus itself has been valuable to catch. Between January and August 2025 alone, common octopus landed on the south coast of the UK was worth an estimated £6.7 million to £9.4 million, and individual vessels have taken in large sums quickly: one Newlyn trawler reportedly landed more than 20 tonnes of octopus over three days, worth an estimated £142,000, a figure that circulated widely in coverage of the report’s release. But that value has gone overwhelmingly to fishermen equipped and licensed to target octopus specifically, while crab, lobster, and scallop fishers, who make up the bulk of the region’s shellfish sector, have absorbed the losses from reduced catches and damaged gear without a comparable upside. The Marine Management Organisation has since been examining what a formal octopus fishery for the region might look like, and Cornwall’s fisheries regulator voted through emergency limits on octopus potting in June, which took effect on 1 July and will run for a year, to manage the pressure the bloom has placed on the wider shellfish stock.
The wider ripple through the food web
The bloom has not stayed contained to fishing boats and pots. Divers and conservationists working the coast have reported Risso’s dolphins moving into inshore waters in larger numbers than usual, apparently drawn by the abundance of octopus as prey, and grey seals have been observed at octopus hotspots, with decapitated octopus remains offering a fairly direct sign of what the seals have been eating. Dan Barrios O’Neill, head of marine conservation at Cornwall Wildlife Trust, has pointed to sea temperature as the likely driver behind the juvenile survival rate underlying the bloom, noting that “the availability of food in the early stages of these animals’ lives is incredibly important as this species grows very fast.” The Wildlife Trusts have described the scale of the increase, relative to a smaller bloom recorded in 2023, as more than a fifteenfold rise in reported sightings.
What happens next is, by the report’s own account, uncertain. The three earlier blooms in the historical record each subsided within a year or two, and there is no established reason to expect this one to behave differently. But the report’s authors were careful to frame their conclusion as a possibility rather than a prediction. Dr Stewart put it this way: “If these conditions persist, octopus blooms could become a more regular feature of our changing seas.” Whether that turns out to be the case will depend on data the region does not yet have, since a phenomenon this rare has, until now, never been studied while it was actually happening.