Work begins on creating a sanctuary for UK “mother oysters”

Published on
June 26, 2019

Scientists have started the first phase of a conservation project to return native oysters (Ostrea edulis) to the Thames estuary in Essex, England.

Having suffered a 95 percent decline in population in the last 200 years due to historic overfishing, the oysters’ recovery has been hindered by habitat loss, pollution, and diseases. With natural replenishment of the native grounds so limited, it was determined that human intervention was their only hope. 

Working in the only marine conservation zone (U.K. marine protected area – MPA) in England for native oysters, the Zoological Society of London (ZSL) chaired Essex Native Oyster Restoration Initiative (ENORI), a coalition of oystermen, local communities, NGOs, universities, and U.K. government, is beginning its project 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 London’s Borough Market and West Mersea, Essex, 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.

“It may not be glamorous work, but laying ‘mother oysters’ at the right time is vital to the success of the restoration program, and therefore vital for the survival of this native British species,” Alison Debney, ZSL’s senior conservation program manager for U.K. and Europe, said.

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.

Oyster farming has been recorded in Mersea since Roman times, with the shellfish forming a staple part of British diets throughout history. However, populations of the European native, or Colchester oyster, have suffered dramatic declines.  

Contributing Editor reporting from London, UK

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