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Marine Science

TORBAY SEAGRASS SURVEYS 2019

TORBAY SEAGRASS SURVEYS 2019

Torbay Seagrass Surveys 2019. Seagrass is a feature of the Torbay Marine Conservation Zone. They are an important habitat for juvenile fish and cuttlefish lay their eggs in them. Species of conservation interest such as the long-snouted seahorse also utilise seagrass habitats. Seagrass beds are thought to have declined by nearly 50% in the last 35 years alone and are a major focus of restoration efforts.

Devon and Severn (D&S) and Inshore Fisheries and Conservation Authority (IFCA) carry out, or assist with seagrass surveys in Torbay biennially to monitor the density and extent of the beds to ensure the current closure to mobile fishing gear (trawls and dredges), via the Mobile Fishing Permit Conditions and Annex 3 and 3a, still protects the beds. This year the Environmental Agency (EA) has carried out seagrass surveys in multiple locations, including Torbay, in collaboration with Natural England. The surveys are part of the development of a Water Framework Directive (WFD) tool to assess the ecological status of subtidal seagrass in estuarine and coastal waterbodies.

It was an excellent opportunity to work in partnership and avoid duplicating survey effort. A day was spent with the EA to assist in the surveying. This is the first seagrass survey to be conducted in the area since 2017. The results from the 2017 survey can be read here.

How was the survey done?

The survey was carried out by the EA on research vessel Three Rivers, which is a 6.2m Cheetah catamaran, using a traditional drop-down camera survey method and a novel echosounder survey.

A survey plan was designed using maps of the seagrass beds provided by D&S IFCA from the 2017 survey. A GoPro Hero 7 camera was mounted onto a 1 m2 drop-down quadrat and at pre-determined points a still image was taken of the seabed and present or absence of seagrass was recorded.

This data can be used to estimate extent and percentage cover and provides ground-truthing for the echosounder work.  The echosounder survey took place using a BioSonics DT-X Extreme Echosounder attached to the side of the vessel. Transects were carried out 20-50m apart covering the full extent of the larger beds. The echosounder survey can be used to measure seagrass extent, maximum depth and density, and is a quick and easily repeatable method.
What were the results of this survey?

The results of the survey will be compiled by the EA and shared with D&S IFCA when complete. D&S IFCA will then use these results to ensure the management currently in place is still appropriate.

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