A day in the life of the freshwater pearl mussel team

Over the Christmas break our freshwater pearl mussel team took it in turns (between festivities) to look after our freshwater pearl mussel adults and juveniles. The oldest juvenile population is now over 7 years old. We have a number of regular tasks to complete monthly, weekly and even daily; supporting and caring for live animals is a 365 day a year commitment, especially when your target species is as critically endangered as the freshwater pearl mussel.

The Freshwater Pearl Mussel Ark project has been running at the Freshwater Biological Association since 2007, holding adult mussels to protect populations against local extinction, and breeding from these adults to provide juvenile mussels for reintroduction. Because this species is so slow growing (taking around 12 years to become sexually mature) we are only now thinking about releasing some of our oldest captive-reared juveniles.

Due to their complex life cycle, rearing freshwater mussels is an interesting and varied process and our activities change depending on the time of year.


Winter tasks focus on routine care for adult and juvenile mussels and their host fish. We also use this time to carry out essential maintenance on our pipe work and rearing systems to make sure they run as they should. Additional tasks include analysing data collected as part of the project and forward planning.

In contrast, on a typical day in May we are busy collecting the juveniles that have made it through the preceding winter and spring on the fish and have started to drop off. Not an easy task as they are only around 0.4 mm long, despite growing by around five times their original body size!  We need to be vigilant at this time to know when to start collecting juvenile mussels to transfer them to trays and grow them on to support their life journey over the next 12 or so years into adulthood.

In August we take delivery of a new batch of host fish and start checking to see if brand new mussel larvae (known as glochidia) can be seen attached to their gills. At this stage there is an incredibly high loss rate; for every 1 million glochidia released, only 400 will successfully attach to a fish host and of these only 20 will survive this stage of their life cycle.


In 2015 the FBA was awarded funding from Biffa Award to make catchment-wide improvements for pearl mussel rivers working with local partners. As part of the Restoring Freshwater Mussel Rivers in England project, we plan to tag juvenile mussels and relocate them back to the catchment from which their parents came. The tags will help us to monitor these new releases over future years.  We want to determine how successful our releases will  be and also to gather more information on such things as the effects of translocating mussels, or to monitor when these individuals become sexually mature.


The work the FBA is doing on freshwater pearl mussels makes every week fascinating and varied for the project team. Even with over 8 years of experience working with these animals we are finding that there is still much to learn about them before we can re-establish viable populations in their native catchments.

A vital part of our work is to share our knowledge, information and passion for the freshwater pearl mussel with as many people as possible, so, if you’re in Cumbria in March 2016, be sure to visit our new exhibition at the Lakes Aquarium.

Watch our video about our research work, see more on our website and follow us on twitter #musselrivers

Louise Lavictoire, Senior Pearl Mussel Project Officer