Getting close to pearl mussels with my underwater camera …

I made one of my regular sampling trips to the River Ehen in Cumbria earlier in the week and took the opportunity to put my new waterproof camera through its paces.  There are plenty of waterproof cameras on the market but I chose a compact Olympus model for the very simple reason that I had been impressed by a colleague’s photos from a similar model.  Not only is it waterproof, but it also has a “super macro” mode that allows you to get to just a centimetre away from your subject.  There is also an LED light source for close-up illumination.  I’ve already shown some images of mosses taken with this camera; my trip to Cumbria gave me the opportunity to try it out underwater for the first time.

A “self-portrait” of my Olympus TG-2 camera

The River Ehen is a particularly good place to put this camera through its paces as it contains England’s largest population of pearl mussels (Margaritifera margaritifera) which have the added advantage for the rookie photographer as they are sessile.  Incidentally, as pearl mussels are protected under the Wildlife and Countryside Act, you need a licence from Natural England to work in the few rivers where they are still found.   I have a licence as I am involved in a scientific study on the river but unauthorised visits to view or photograph pearl mussels here or elsewhere could be construed as a criminal offence.

Both of these populations were photographed in about 30 centimetres of water.  The right hand population was located in a faster-flowing section of the river – indicated by the absence of silt and algae on the shells.   You can see the two siphons on the mussel at the centre of the left hand image through which the mussel inhales and expels water and particulate matter.  The gills are not only used for respiration; they also capture food particles from the water and pass these to the digestive system.

Pearl mussels (Margaritifera margaritifera) in the River Ehen, Cumbria, photographed in situ using an Olympus TG-2 camera.  The largest mussels are about 4-5 centimetres across.

The situation in the River Ehen has improved since I last wrote about the pearl mussels here (see “Pearl mussels in the River Ehen” from January 2013).   Back then, most of the mussels in the river looked like those in the left hand image; now the cleaner mussels on the right hand side are more typical in many parts of the river.   This is partly due to the higher discharge in the river which, we think, is gradually flushing the fine sediment out from the interstices between the gravels and pebbles, allowing oxygenated water to circulate through and, we hope, allowing the young mussels to thrive.  However, as the earlier post explained, the pearl mussel life cycle is very long and delicately balanced, so there is no reason to be complacent.   Over half of the world’s healthy populations of the pearl mussel are found in the UK so a lot of attention is being paid to the few remaining rivers where it thrives.