New South West Marine Ecosystems Report highlights the unusual marine events of 2023

12 August 2024

This comprehensive, 138-page report provides a timely update on the status and recent trends observed in the seas around the Southwest UK in 2023, and this year celebrates its 10th year. It is also a unique report in that it is the only marine communitiy initiative in the UK bringing together intelligence from a wide range of stakeholders, including scientists, conservationists, industry, environmental regulators and local citizens.

The report features chapters on oceanography and plankton headed by PML scientists Prof. Tim Smyth and Prof. Angus Atkinson MBE.

These chapters describe the exceptional marine heatwaves during early summer 2023 and the unprecedented blooms of salps (gelatinous filter-feeding zooplankton) later in the summer. This information provides vital context for the later chapters that cover: seashore and seabed; fish and turtles; seabirds; seals; cetaceans; fisheries; Marine Protected Areas; water quality; marine planning, and marine plastic pollution.

Prof. Angus Atkinson MBE, Senior Marine Ecologist at Plymouth Marine Laboratory, said:

“The great thing about the South West Marine Ecosystems Reports is that they are so up to date. Most reporting of marine ecosystems covers trends that have happened several years previously, but these annual reports are from just the previous year, framed in the context of longer-term trends”.

Summary of each chapter

Oceanography. The year started with relatively warm conditions throughout the water column with temperatures around 9.5 °C off Plymouth.  This cooled to the minimum recorded temperature (for 2023) in mid-March of 9.3 °C.  June 2023 was noteworthy in that sea surface temperatures were 2 – 3 °C above the long-term (1991-2020) mean in the Celtic Sea and 1 – 2 °C above the long-term mean in the western English Channel. By late June off Plymouth, surface waters were around 17.8°C and, at depths below 30 m, around 13.9 °C; both associated with a sustained meteorological (and marine) heat wave. Contact: Tim Smyth, tjsm@pml.ac.uk.

Storms.  The patterns of storms in the spring of 2023 were unremarkable but were more normal in the autumn of 2023 and in the winter of 2023 to 2024. There were very few named storms in the January – April period of 2023. The impact on natural systems, species and habitats was on the unremarkable side of normal, but seal pups and juveniles were seriously affected by the autumn storms in 2023. Contact: Bob Earll,  bob@bobearll.co.uk.

Plankton. There were unusual reports in terms of numbers and geographic extent of both salps (colonial cousins of seasquirts) and hydrozoan ‘Crystal Jellyfish’ Aequorea sp(p) in late summer in the English Channel.  Whilst blooms of both have previously been recorded, they have not been concurrently reported at so many different locations. Sightings of true jellyfish in 2023 revealed similar patterns to those seen in previous years with barrel jellyfish making a return, having been only rarely reported in 2022. Contact: Angus Atkinson (for general plankton), aat@pml.ac.uk. Jeanette Sanders (f­or observations of jellyfish), sea@seadreameducation.com.

Seashore and seabed marine life.  There were no increases in extent or abundance of warm water species that might suggest significant climate change effects although a record of eggs of a Common ('Mediterranean') Octopus suggests that they are breeding in our waters. There were declines in the occurrence and abundance of some species including, conspicuously for divers, of cold-water Plumose Anemones in inshore areas. Contact: Keith Hiscock, khis@mba.ac.uk.

Fish. Sharks: On 1st May, a c. 293 cm subadult female Smalltooth Sand Tiger Shark was found floating dead off Lyme Regis. The observation followed one found stranded in Hampshire and about 320 km north of any previous record. Boney fish: The recent pattern of changes continues with several less familiar species becoming more established around south-west England: these include variable blennies, combers and axillary sea breams. Contacts: Douglas Herdson, Douglas.Herdson@btinternet.com and Simon Thomas (sharks and rays), patsmithdatabase@gmail.com.

Reptiles. 2023 saw the most turtles recorded in the south-west area for nine years. The majority of the reports were of juvenile Loggerhead or Kemp’s Ridley turtles, most of which were ‘cold shocked’. Contact: Douglas Herdson, Douglas.Herdson@btinternet.com.

Marine and coastal birds. 2023 saw continued increases in burrow-nesting seabirds and auks: both continuing to benefit from rat eradication on Scilly and Lundy. ‘Bird flu’ badly affected terns and black-headed gulls in Dorset, but there was good news for sea-watchers with thousands of southern-breeding shearwaters flooding into the south-west in late summer. This included an estimated 16,000 Cory's shearwaters in one day off Scilly. Contact: Alex Banks, alexnbanks@gmail.com.

Seals. More seals were recorded dead across Cornwall in 2023 than born (half the dead seals were less than a year old). The largest seal disturbance on record and caused directly by people, saw 250 seals stampede off two adjacent Site of Special Scientific Interest (SSSI) beaches, resulting in an enforcement letter from Natural England. Contact: Sue Sayer, sue@cornwallsealgroup.co.uk

Whales, dolphins & porpoises. There continued to be high numbers of cetaceans inshore in 2023. Since 2015 there have been marked increases in many cetacean species in inshore waters. There is limited ongoing research investigating this shift and cetacean research in the UK continues to be poorly funded. Contact: Duncan Jones, duncoliver@yahoo.co.uk (toothed whales and dolphins) and Dan Jarvis (Baleen Whales), dan@bdmlr.org.uk.   

Fisheries. In 2023, the landings of many traditional fisheries such as brown crab and mackerel continued to decline, whilst landings for other species such as crawfish and spurdog increased as a result of stock recovery. Analysis undertaken by the Marine Management Organisation (MMO) showed an overall reduction in the quantities of fish and shellfish landed in the south-west since 2016. It is likely that climate change will continue to benefit some species, such as black seabream, red mullet and anchovy and to result in declines of some other species, such as lemon sole, Atlantic cod, haddock and megrim. Contact: Libby West,  Libby.West@naturalengland.org.uk.

Marine protected areas. Currently 81% of Marine Protected Areas (MPAs) within the Inshore Fisheries and Conservation Authorities (IFCA) Devon and Severn area are closed to bottom-towed gear, compared to 75% in the Isles of Scilly and 40% in Cornwall. The Marine Management Organisation (MMO) is responsible for introducing fisheries management measures to all offshore MPAs by the end of 2024. There is an increasing recognition of the need to adopt a whole site approach to MPA management for effective marine nature recovery. Contact: Carli Cocciardi, cocciardi@devonwildlifetrust.org.

Water quality. The year 2023 was the sixth wettest on record contributing to a higher percentage of sewage overflow spills. One hundred percent of storm overflows have now, however, been fitted with event duration monitoring devices which will allow complete coverage, real-time data and targeted improvements. Contact: Eleanor Ward, Eleanor.Ward@devon.gov.uk.

Marine planning. ‘The Marine Planning Monitoring Surveys 2023’ two-page Summary Report revealed that, overall, the Marine Management Organisation’s (MMO) South West Marine Plan remains widely utilized by a diverse array of stakeholders for decision-making and supporting development proposals. Policies related to biodiversity and heritage are among the most frequently applied. The development of floating offshore wind turbines represents a significant technological advancement and demonstration projects are anticipated to be operational within the next few years, with further commercial deployments in the pipeline. Contact: Mae van Loef, mae.vanloef@marinemanagement.org.uk and Ellie Hoad, ellie.hoad@marinemanagement.org.uk.

Marine plastics. Excellent volunteer work continues in the southwest to remove plastics from the marine environment. Analysis of debris from coastal cleans in 2023 by the Clean Ocean Sailing (COS) organisation also highlighted high density polyethylene (HDPE), plastic bottles and nets and ropes to be the most commonly removed debris. Contact: Dan Wilson, d.wilson@exeter.ac.uk and Delia Webb, deliawebb@btinternet.com.
 
The annual South West Marine Ecosystems (SWME) Conference brings together the marine and coastal community, to discuss the changes that are taking place in our local seas.
 
Webinars on the key topics for 2023 can be viewed on the SWME YouTube channel >>
 
Since the SWME Conference, new research has also shown that while high-pressure weather conditions were the main driver behind the elevated sea temperatures of the coastal waters of northwest Europe in June 2023, warming due to climate change made it reach category II (strong) instead of I (moderate). Read more here.  
 
 

Related information

State of South West Seas 2023 Report
 

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