So did it actually work?

Emily Collins – Conservation Student Intern 

It’s eleven o’clock and the sun is already high in the sky above Lealholm stepping stones. There are two benches overlooking the river; one occupied by a couple of ice-cream savouring villagers, the other piled with buckets, Environment Agency fleeces and a hefty lot of electrofishing equipment. It’s time, at last, to find out whether last year’s bankside encystment really worked…

The plan is simple; the Environment Agency team will use their electrofishing kit to stun the fish, capture them in their net and place them in a bucket for us to examine. Freshwater Pearl Mussel glochidia – if present – will be visible on the gills of the fish as little white specks. Whilst Simon the River Esk Project Officer takes charge of handling the fish, it is my job to record whether it is a salmon or trout, its age, and whether or not it has glochidia on its gills.

In April 2014 we had followed the same routine, only to find that not a single fish showed signs of mussel encystment on their gills. This was more than a little disheartening, especially as this area of the Esk is prime habitat for juvenile survival. If young mussels aren’t growing on the gills of the fish then chances are they’re not growing in the riverbed either. Considering that our mussels are all the equivalent of old-aged pensioners and that it takes 10-15 years for a mussel to mature, this is a huge concern for us. Hence the decision to try out bankside encystment that summer.

Fingers crossed!

Amazingly, it turns out that this time around, 1 in 4 fish (mostly salmon) had glochidia on their gills. Whilst numbers were low – approximately 4 to 6 glochidia on each fish – this is a great improvement since last year and an important indication that our mussel old-aged pensioners have still got it in them to reproduce. With this in mind, we’re already looking to carry out another bankside encystment this August to further their success.

In the meantime, there is the potential for transferring some of our juvenile mussels from the Freshwater Biological Association ARK facility back into the River Esk. Of course, there’s no point in doing this until the river habitat is suitable for mussel survival so, with the help of landowners, contractors and volunteers, we’re continuing to plant riparian trees, control invasive species, carry out bank stabalisation and fence along the river bank in order to reduce the sedimentation in the water and ultimately, improve mussel habitat.