New report reveals scale, causes and consequences of South West octopus bloom

Researchers from across Plymouth comprised the new report which draws on data from scientists, fishermen and citizen scientists
The common octopus is native to UK waters but is typically rare, favouring warmer seas further south in Europe and the Mediterranean

New report reveals scale, causes and consequences of South West octopus bloom

Researchers from across Plymouth comprised the new report which draws on data from scientists, fishermen and citizen scientists
Keith Hiscock MBE

A new report has revealed that a dramatic population bloom of the common octopus (Octopus vulgaris) off the South West coast is having significant effects on fisheries and marine ecosystems.
The common octopus is native to UK waters but is typically rare, favouring warmer seas further south in Europe and the Mediterranean. Only four major population blooms have been recorded in the past 125 years – in 1899-1900, 1932-33, 1950-51 – with the current bloom, which really accelerated from January last year, appearing to be at least as extensive as any previously recorded.
A study examining it was conducted by researchers from the University of Plymouth, the Marine Biological Association (MBA), Plymouth Marine Laboratory (PML) and an independent consultant. Funded by Defra, Plymouth City Council and Devon County Council, it draws on data from scientists, fishermen and citizen scientists.

This is an extraordinary event that tells us a lot about how marine life is responding to a warming ocean, and the survey reveals the mixed effect that this has had on fisheries.

Establishing the full effect of the current bloom on other species such as crabs, lobsters and scallops will require further research and monitoring. If these conditions persist, octopus blooms could become a more regular feature of our changing seas. Understanding their causes and consequences is vital to help both ecosystems and coastal communities adapt. This is not just a fisheries story; it’s an ecosystem story. We need to understand how these octopus blooms affect everything from shellfish stocks to top predators, and how to adapt in a rapidly changing ocean.

Bryce StewartDr Bryce Stewart
Associate Professor at the University of Plymouth and Senior Research Fellow at the MBA

Climate link and cross-Channel connections

The research team found that unusually warm sea temperatures during bloom years and the preceding year were a consistent factor in all recorded blooms. Sustained easterly winds may have helped transport young octopus larvae from the Channel Islands and northern France. Ocean current modelling supports this, showing that larvae from Guernsey, which has seen its own octopus bloom since 2024, likely contributed to the UK surge.
A survey of 40 fishers revealed mixed impacts from the octopus surge. While some adapted to catching octopus and benefited economically for a period of time, over half reported negative impacts, particularly those targeting brown crabs, lobsters and scallops, which suffered heavy predation from the octopus. Catch rates for those species dropped by 30% to 50% in 2025. Concerns are therefore growing about long-term damage to crab, lobster and scallop stocks. 

Looking ahead: monitoring, modelling and management

The report calls for continued monitoring through MBA trawl surveys, University of Plymouth BRUV work, and enhanced Cefas stock assessments. It also recommends the proposed OctoPulse model of ocean conditions, which was developed at Plymouth Marine Laboratory; early detection of octopus larvae in plankton, and easier ways for fishermen to report sightings via apps or digital systems.
Multiple reports of octopus breeding and sightings of juveniles in UK waters in 2025, previously almost unheard of, suggest the current bloom may continue or reoccur again soon. The team stresses the need to help fisheries adapt to the changing abundance of different species, and recommends further research into how sudden influxes of previously rare species affect marine ecosystems under climate change.

As a result of our long-term monitoring datasets we have a great opportunity to measure changes in the octopus population to inform sustainable ecosystem scale management. It is essential that we monitor any changes in abundance, distribution and movement, and that we assess octopus relationships with other species such as useful associates, prey or predators.

Emma SheehanProfessor Emma Sheehan
Professor of Marine Ecology

The report concludes that octopus blooms could become a regular feature of UK seas, requiring support for gear adaptation and sustainable fishery development.
  • The full report - Common octopus (Octopus vulgaris) blooms off the Southwest of the UK: History, trends, causes and consequences. Report on Work Package 1: History, causes and consequences of octopus blooms - is available to read at https://www.plymsea.ac.uk/id/eprint/10535/.
 

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