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Sunday, 15 March 2015

Freshwater Pearl Mussels

Initial training on the Torridge
 The Freshwater Pearl Mussel (Margaritifera margaritifera ) is in severe decline, under both habitat and exploitation threats despite being heavily protected! There are still large (1000s) numbers in Scotland and Yorkshire but here in the only other area of the UK with any populations the numbers are much less (100s). Those that are know about are literally clinging on in the Torridge and its tributaries.


Last Wednesday (11th March) I undertook a day's training hosted by North Devon Nature Improvement Area/Biosphere staff to learn how to survey for potential breeding sites. We ten volunteers, from a variety of backgrounds, met with five experts representing the Environment Agency, Devon Wildlife Trust and North Devon Biosphere, on a secluded stretch of the River Torridge.


Old, dead Freshwater Pearl Mussel
During the morning we were shown how to record along a stretch river noting various parameters – Habitat type – which describes the state of the river channel; Bankside features and Special feature points. This last covers things like the presence of macrophyte beds, river width, water quality, extraction, exposed bedrock, bars and evidence of key species – Kingfisher, Otter and Dipper, and of course Mussels themselves all of which was done from the bank accompanied by our tutors.

This was followed by us practising what we had learned in groups of 2 or 3. We retraced the same stretch of water making our own observations on the recording sheet. This stretch does have an existing colony of Freshwater Pearl Mussels so we were recording parameters that were relevant to the species' existence. We all met up and compared, and where necessary, amended our surveys.

After lunch, each group was allocated a new stretch of river to survey in earnest. We did hear a Dipper and saw Kingfishers as well as tracks and spraints of Otter. Most excitingly, two keen-eyed surveyors found old, dead Mussels from the strand line on a couple of the river bars. They are surprisingly large.

We now await the call to spread out further along the river and begin using our new survey skills for real.

Individual teams surveying
Freshwater Pearl Mussels live for around 100 years and breed, in suitable habitats at 12-20 years of age. The population in the UK is described as moribund with no proven breeding having taken place in the last 40 years. Time is running out so we are helping to prove that the survey methods can correctly describe and identify the essential features of Mussel beds so that measure to prevent silt accumulation, overshading, flooding or damage which can prevent recruitment or breeding or kill them can be developed. A 3-year project officer post is expected to move this vital work forward before it is too late.

As well as helping in this critical work it was an opportunity to walk along and enjoy a beautiful stretch of one of Devon's enigmatic rivers.


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