PEARL MUSSELSThe freshwater pearl mussel (Margaritifera margaritifera) 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 and it is now listed as critically endangered as most former populations are 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
- Water quality problems (especially high nutrient levels of Nitrogen and Phosphorus)
- Decline in populations of host fish (salmon and trout)
- 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 mussels in the Esk have not produced young for over 40 years and it is likely that the Esk population will become extinct in the next 25 years unless action is taken to halt this decline.
The Esk Pearl Mussel and Salmon recovery project led by the North York Moors National Park is working to improve the river habitat, restore the pearl mussel population, increase populations of salmon and trout and promote good land management within the catchment.
Vital work to safeguard the freshwater pearl mussel has included taking several adult mussels from the River Esk to a special captive breeding facility in the Lake District. The facility provides an ‘ark’ to conserve dwindling populations of the freshwater pearl mussel and to rear juvenile mussels through captive breeding, ready for reintroduction back to the River Esk in future years.
Further details of the project can be found on the North York Moors National Park website http://www.northyorkmoors.org.uk/looking-after/our-projects/pearl-mussels or by contacting Simon Hirst, River Esk Project Officer, at the North York Moors National Park firstname.lastname@example.org.
SALMONYERT plans to continue the re-stocking programme for salmon, using Esk brood stock and the hatchery facilities at Kielder. We are now some 14 years into the project and the ratio of salmon to sea trout in the river has begun to indicate a degree of success.
Electrofishing on The River Esk
HYDRO POWERFollowing a period of consultation, in November 2012 a low head hydro power scheme was commissioned at Ruswarp. This is run by an organization called Esk Energy. Significantly the hydro is located at the confluence of tidal and fresh waters and is therefore of crucial importance to both upward and downward migration of fish.
Whilst the hydro scheme was being built, the existing fish pass was refurbished and a Larinier fish pass installed.
The Environment Agency have undertaken to carry out 3 years pre installation monitoring and 3 years post installation monitoring so as to determine the effect on fish migration. This programme will be completed by the autumn of 2015.
YERT and a representative from the Esk Riparian Owners/ Anglers Group attend regular monitoring meetings together with representatives of the Environment Agency, Esk Energy and the North York Moors National Park. At these meetings any operational concerns regarding the turbine can be raised and importantly data from the monitoring programme scrutinised.
(Salmon image © Esk Fisheries Association)