North York Moors

North York Moors logo
Browse section

Pearl mussels

Pearl MusselPearl Mussel

Pearl Mussel and Salmon Recovery work

The freshwater pearl mussel is one of the longest-lived invertebrates known, and can live for more than 100 years. Formerly widespread and abundant in England and Wales, its numbers have severely declined with most former populations now on the verge of extinction.

The decline in pearl mussel populations is due to a number of factors:

  • Habitat degradation caused by sedimentation of river gravels.
  • Decline in populations of host fish (salmon and trout).
  • Water quality issues.
  • Historic Pearl Fishing

The pearl mussels in the River Esk are the last surviving population in Yorkshire, and only a few mussels are left. The vast majority of the remaining pearl mussels are aged 60 years+, and the mussels in the Esk have not produced young for over 25 years, it is likely that the Esk population will become extinct in the next 40 years unless action is taken to halt this decline.

Pearl mussels are a very important 'indicator species', which show us the health of our river systems. When species like this start to disappear, then we know that all is not well with the river eco-system.


Funding has been obtained from the Environment Agency/Natural England's Water Environment Grant for further work for two years from April 2019. The project has been funded through a number of other sources since 2008 including Biffa Award (Restoring Freshwater Mussel Rivers in England), WREN Biodiversity Action Fund, the Heritage Lottery Fund, Yorventure, Environment Agency, LEADER and the North York Moors National Park Authority.

Useful information to download

River Esk water friendly farming - good practice guide (pdf)


Elizabeth Clements, Head of Natural Environment
01439 772700