Essex estuary to be sanctuary for ‘mother oysters’

Conservation coalition begins restoration of UK’s largest protected area for native oysters.

Vital work to save an Essex icon begins this month – as the ZSL-chaired Essex Native Oyster Restoration Initiative (ENORI) begins its 2019 conservation activities in the Thames estuary – creating the region’s first Mother Oyster Sanctuary.

Suffering a 95% decline in population in the last 200 years due to historic overfishing, the oysters’ recovery has been hindered by habitat loss, pollution and the introduction of diseases. Natural replenishment of their native grounds is so limited that human intervention is their only hope. 

Working in the only Marine Conservation Zone (UK marine protected area) in England for native oysters, the ZSL chaired ENORI - a coalition of oystermen, local communities, NGOs, universities and UK Government – will begin by creating the habitat required for the Mother Oyster Sanctuary, replenishing the estuary’s lost oysters.

‘Recycled’ shells from oysters bred in Mersea and sold in Borough Market and West Mersea as well as cockleshells from the Thames cockle fleet have been used to “lay the cultch” – a colloquial term used to describe the process of laying crushed shells and stones onto the estuary floor. This step is needed, as oysters require a hard surface to grow on, which is not naturally found on the muddy estuary beds in Essex. 

Once the “cultch laying” is completed, adult females or ‘mother oysters’ are laid, which when conditions are right, will spawn in the coming weeks; initiating the first stages of the native oyster’s life cycle.

Oyster farming has been recorded in Mersea since Roman times, with the shellfish forming a staple part of many Brit’s diets’ throughout history. However, populations of the European native, or Colchester oyster (Ostrea edulis) have suffered dramatic declines.

ZSL’s Senior Conservation Programme Manager for UK & Europe, Alison Debney, said: “It may not be glamorous work, but laying ‘mother oysters’ at the right time is vital to the success of the restoration programme, and therefore vital for the survival of this native British species. 

“ENORI was founded in 2013 by the conservation coalition in an attempt to restore a nationally important breeding population that once supported hundreds of fishermen. 

“The coalition has since moved more than 25,000 native oysters to Essex estuaries, as well as ensuring that fishing in the area is prohibited until the oyster stocks have sufficiently recovered and are able to withstand sustainable harvesting.” 

Known as ‘ecosystem engineers’ because they create the conditions for other species to thrive – stabilising shorelines, filtering water and providing vital food and habitat for coastal wildlife. One adult oyster, for example, can filter more than 140 litres of water in a single day. 

Dr Rebecca Korda, Senior Marine Advisor at Natural England explained: “We are thrilled to be part of this collaboration which saw an array of stakeholders coming together and showing incredible innovation and drive to work to restore the native oyster and the native oyster beds back to the Essex waters. This is a hugely exiting and important step in taking this work forward and we are delighted to continue to support and contribute to the project”.

Rachel Langley, Living Seas Co-ordinator at Essex Wildlife Trust said: “We are delighted that this exciting project is evolving into its next phase and we have no doubt that the outcome of ENORI’s pioneering restoration work will be extremely positive for the Native oyster population and subsequently the marine ecosystem in Essex.”

ENORI is a joint venture between ZSL, Essex Wildlife Trust, Blackwater Oysterman’s Association, Blue Marine Foundation, The University of Essex, The Nature Conservancy, River Roach Oyster Company, Colchester Oyster Fishery, CEFAS, Natural England, the Environment Agency, and the Kent and Essex Inshore Fisheries Authority (KEIFCA).

Find out more about our Thames conservation work