Latest research looking at the role of sediment in the decline of Selsey fishing catches is completed

The CHASM project (Crustaceans, Habitat and Sediment Movement) which is led by Chichester District Council, was established in 2020 in direct response to concerns raised by the Selsey fishing community. The aims are to find out the causes behind the decline in crab and lobster catch as well as changes in sea water and habitat quality, and the increased quantity of marine sediment seen locally and elsewhere on the UK south coast.

The report seeks to understand environmental change from a sediments perspective, and sets out to answer a series of questions using various data sources and analysis.

The recent report, carried out by the University of Southampton and led by Dr Charlie Thompson, examines sediment mapping and the data gathered from a series of probes called sonde units. These were located in Medmerry, Pagham and Chichester harbours, and in four locations in the sea round the peninsula.

The data gathered helped show how various environmental parameters have changed over time.

These sensors measured water clarity; oxygen; levels of chlorophyll; water temperature; and fluorescent dissolved organic matter (fDOM) - a technique often used to monitor wastewater discharge.

Key findings outlined in the report are:

• Fine sediment deposited locally from dredging is thought to reach the CHASM project area, which includes Bracklesham Bay and Selsey Bill.
• It is not known whether the fine sediment contains contaminants - this will be another tranche of future work.
• Coarse sediment is not thought to be an issue.
• A better understanding of the organic/biotic component of the environment and water quality should be sought.
• An understanding of the limiting factors should be sought, by understanding changes in nutrient sources (for example. from agricultural run-off and sewage).
• Algal blooms can lower oxygen levels, as seen during one particularly hot summer, and may potentially damage aquatic life.

"This important scientific research is another key step forward in understanding why changes have been taking place," explains Councillor Jonathan Brown, Cabinet Member for Environmental Strategy at Chichester District Council. 

 "Before solutions can be found we first need look at exactly what the changes are and the reasons behind them. The CHASM project is looking at all the possible environmental reasons behind these changes, and very fine sediment is likely to be one of the contributing factors. The report sets out to answer a series of questions relating to this.

"A lot more scientific research needs to be carried out and further research is currently being undertaken by the University of Brighton, as part of their Sussex Estuaries Project. Further work on the role of sediment is being planned by the Blue Marine Foundation.

Councillor John Cross, Cabinet Member for Culture, Sport and Place at Chichester District Council. says: "The CHASM report is a prime example of how partnership working can bring different groups of people together to answer questions posed by a community, in this case the Selsey fishing community which has a rich history going back to the Bronze age and which has played an important part in the area's local economy.

"The CHASM project is largely unfunded, but small pockets of funding from local sources and huge contributions in time and resources from other groups has enabled CHASM to complete this first key step in understanding what has been happening to the crab and lobster beds and I'd like to thank the University of Southampton for their time and work on this.

"I'd also like to say thank you to other partners including the Channel Coastal Observatory, the University of Brighton, in addition to over 20 national, regional, and local environmental organisations with interests in marine conservation."

Funding and equipment for this stage of research was gratefully received from:

• The FG Woodger Trust: written report and data analysis
• East Wittering & Bracklesham Parish Council and West Wittering Parish Council: sonde units placed outside Pagham Harbour and Medmerry.
• FG Woodger Trust and Sussex Wildlife Trust: sonde units in Chichester Harbour.
• Environment Agency: contributed sonde and telemetry units as part of a pilot project investigating equipment use in the marine environment.

Specialist advice and input was delivered by Chichester District Council; Chichester Harbour Conservancy; Environment Agency National Water Quality Instrumentation Service (NWQIS); the Manhood Peninsula Partnership; Mulberry ME; Selsey fishing community; Southsea Sub Aqua Club; University of Brighton.

People can read the report and more about the CHASM project on Peninsula Partnership's web page (opens new window).

Date of release: 12 February 2025

Reference: 4435