Isles of Scilly trawling impact study on reef sediment veneer habitats

applied Marine Ecosystems Research and Marine Conservation Research Group
Research boat in the Scillies

Assessing the impact of bottom-towed fishing on sediment habitats

In the past decade, there has been very little mobile fishing in the Isles of Scilly waters due to perceptions of low economic returns and availability of fishing grounds elsewhere. Renewed interest from a small number of fishing vessels has created a unique opportunity to conduct a ‘before, after, control and impact’ (BACI) study of mobile fishing in the Isles of Scilly. Studies rarely have the chance to survey ecosystems prior to disturbance and are therefore often limited to drawing spatial comparisons between impacted and unimpacted areas, which are usually confounded by other environmental variables. However, the low historic fishery exploitation paired with the anticipated return of trawling has created the UK’s first chance to study how trawling activity changes the ecosystem.
The applied Marine Ecosystems Research Unit are measuring the impact of mobile fishing gear to offshore sediment habitats, relative to a baseline. We plan to also assess levels of blue carbon using state-of-the-art technologies as well as collecting long-term data on changes to infaunal, benthic and mobile populations. Data collected will provide the opportunity to understand trends in subsequent recovery of offshore sediment habitats following disturbances.
In the summer of 2023, the University of Plymouth returned to the Isles of Scilly and conducted surveys with Isles of Scilly IFCA and Cornwall IFCA. Baseline data were collected at sites off Scilly that have not been trawled since 2010. The team conducted research using non-invasive technology (baited remote underwater video and towed underwater video) to survey habitats and species at depths of > 90m. These data will provide a current picture of the condition of these habitats prior to the resumption of trawling activity and the biodiversity of species within them. Survey sites will be continually monitored in the coming years to build a long-term picture of fishing impacts in the Isle of Scilly.
This survey will provide the UK’s first evidence base for assessing the impact of bottom towed fishing on sediment habitats with pre-disturbance controls.

Recovery of Baited Remote Underwater Video gear on Research Vessel Tiger Lily VI Researchers from the University of Plymouth conducting the Isles of Scilly survey

Researchers setting ROV in the ocean near the Isles of Scilly Recovery of Baited Remote Underwater Video gear on the Cornwall IFCA’s Research Vessel Tiger Lily VI

Researchers setting ROV in the ocean near the Isles of Scilly Recovery of the Towed Underwater Gear on the Cornwall IFCA’s Research Vessel Tiger Lily VI

Background to the new Byelaw and trawling activity on Scilly

The Isles of Scilly is an archipelago off the coast of Cornwall, host to a rich array of habitats and wildlife which support a small-scale fishery, a thriving marine recreation sector, and significant tourism. Extensive seagrass beds, rocky reefs, sandbanks, and mudflats support ecologically and economically important species at various stages of life. The management of these important habitats has required a dynamic approach, which has changed in response to improved scientific evidence and changing resource use. Conservation designations comprise three Marine Protected Areas: The Isles of Scilly Special Area of Conservation, Marine Conservation Zone and Special Protection Area.
Due to substantial historic and ongoing marine exploitation in the UK and globally, a major roadblock facing marine management is the scarcity of unimpacted marine habitats. Such unexploited habitats are crucial reference sites against which to measure both the impacts of human activities and the success of marine management strategies. Without appropriate low-impact reference sites, shifting baselines lead to lower expectations and ambitions for marine conservation. The Isles of Scilly represent a unique area of relatively low human impact, thanks in part, to the isolation of these islands from mainland UK and their low local populations.
A previous project (Site Classification to Inform Sustainable Lives and Livelihoods for Fisheries and Ecosystems (SCILL-E) project) led by the University of Plymouth, surveyed nearshore and offshore marine habitats in the Isles of Scilly along with their biological communities. Marine sampling techniques such as side-scan sonar, towed underwater video (TUV), baited remote underwater video (BRUV) and grab sampling were used to develop a detailed picture of these marine communities. A range of critical habitats were identified, including sediment veneers, which are defined as reef species emerging through a thin layer of sediment signifying the presence of underlying bedrock.

Timeline of activity

2013 – In response to the ‘Revised Approach’ the Isles of Scilly Inshore Fisheries and Conservation Authority (IFCA) passed a new byelaw to limit mobile gear activity within the Isles of Scilly district and Special Area of Conservation (Map 1).

2018 – The Isles of Scilly IFCA recognise the need for a review of this byelaw to provide greater strength and flexibility and commission the University of Plymouth to undertake surveys and an ecosystem service asset and risk assessment to help guide and inform decision making. The surveys identified some previously unknown deep reef veneer habitats to the east of the islands which were an important driver for increasing the extent of the no-trawl zone.

2023 – A new Byelaw is pending approval within the Isles of Scilly district, defining a large no-trawl zone of 398km2 encompassing all currently designated sites and prohibiting trawling in 43% of the district.

Isles of Scilly Complex Spatial Management Boundaries Map 1 – Isles of Scilly Spatial Management Boundaries

Image captured by the Towed Underwater Video camera Image captured by the Towed Underwater Video camera

Image from the Baited Remote Underwater Video camera, Scillies Image captured by the Baited Remote Underwater Video camera

Investigating crawfish population recovery in the Isles of Scilly

From 2021–2023 University of Plymouth worked closely with the Isles of Scilly IFCA to deploy a network of 16 acoustic telemetry sensors over an area of 2km2 as part of the FISH INTEL project. The work was conducted to assess the efficacy of Marine Conservation Zones in protecting recovering crawfish populations across the islands. Workshops and training were provided to local interest groups on how to tag crawfish with acoustic telemetry transmitters. Across the research period, a total of 82 crawfish were tagged with acoustic tags and released. Following release, the data from tagged crawfish has highlighted they are highly sedentary and do not often move further than 1km from their core territory. University staff will continue to work with Isles of Scilly IFCA to analyse the tracking data to help improve or better inform local management of this charismatic species.

Timeline of activity

2021 – 12 acoustic receivers deployed to the east of St. Martins island and 31 crawfish tagged.

2022 – University of Plymouth researchers return to the Isles of Scilly to maintain receivers and deploy an additional four receivers. A further 51 crawfish were tagged.

2023 – Receivers were retrieved and a two-year dataset on crawfish movements in the Isles of Scilly was recovered for analysis.

A tagged crawfish A tagged crawfish

Gathering data on crawfish Gathering data on crawfish

An acoustic receiver ready for deployment An acoustic receiver ready for deployment

People

The SCILL-E Project (Site Classification to Inform Sustainable Lives and Livelihoods for Fisheries and Ecosystems)

This project represents an opportunity to further trial the natural capital approaches developed in the North Devon Marine Pioneer and support the IFCA to propose management measures that benefit a sustainable and secure fishing industry.
SCILL-E Project

FISH INTEL Interreg France (Channel) England

Our cross-Channel partnership uses innovative underwater acoustic tracking technology to identify the environmental conditions a range of important marine species need in order to thrive.
The €4.1million FISH INTEL project, supported by €2.8million from the European Regional Development Fund via the Interreg France (Channel) England programme, focuses on a series of sites along the coastlines of southern England, northern France and Belgium.
Fish intel