Ageing Mussels

Simon Hirst – River Esk Project Officer

As mentioned previously, the River Esk in the North York Moors is the only river in Yorkshire with a Freshwater pearl mussel population Margaritifera margaritifera. The population is estimated to be comprised of approximately 1,000 individuals and is in drastic decline, so much so that it is on the verge of extinction. The decline is due to a number of linked causes such as water pollution, choking of the river bed by sediment build-up, deterioration in fish numbers and habitat degradation.

A dense bed of healthy adult mussels in Scotland. Copyright Sue Scott - SNH,

We’re working to improve the riparian habitat and so help secure the local population of Freshwater pearl mussel in the River Esk. We recently sent a sample of mussel shells from the Esk* over to the Swedish Natural History Museum in Stockholm, in order to determine the age of the mussels in the River Esk. The maximum age of Freshwater pearl mussels in the wild has been shown to vary considerably, from a low of 35 years in Spain (warmer, lower latitude rivers) to over 200 years in arctic areas (colder and high latitude rivers). Information from the ageing study would tell us how long we have left to save the Esk population from extinction and help identify the approximate time when the River Esk mussel population went into decline.

Dr Elena Dunca from the Swedish Natural History Museum sectioned (cut though) the shells supplied and then counted the growth lines on the mussel shell using a high powered microscope.

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Growth lines visible on the freshwater pearl mussel shell.

Esk FWPM - Age and length graph - Swedish Natural History Museum

This age/length graph will allow us to age fairly accurately any mussels we find in the wild in the future just by measuring them.

A total of 10 shells were aged by Dr Dunca, and the graph below shows that the mussels sent to Sweden ranged in age from 45 to 88 years of age.  The mussels in the River Esk also showed normal growth rates.

Esk FWPM - Length frequency graph - Swedish Natural History Museum

Length frequency graph of mussels in the River Esk

The smallest live mussel we have found in the Esk up to now was 75mm (approximately 28 years of age). This means the last time the Esk mussels reproduced successfully in the wild was in the late 1980s. The largest mussel we have found in the Esk was 156mm (approximately 100 years of age), which means it was born around the time of the First World War. The vast majority of the mussels are around the 130mm-140mm size range (approximately 80 years of age). We now know for scientific certainty that the Esk has an ageing population in need of help!

The best hope for our mussels is for them to start to successfully reproduce again. We’re working with the Freshwater Biological Association (FBA) who are carrying out captive breeding work in the Lake District. We hope to re-introduce the captive bred young Esk mussels from the FBA Facility back into the Esk once the riparian habitat is restored enough to sustain them, and so ultimately stop this species from becoming extinct in the wild (of Yorkshire).

* Please note – No mussels were harmed in the making of this study! We used empty shells that were found on the banks of the Esk.

Thanks to our funders at Biffa Award, for their support to carry out this vital research work.

Biffa

Biffa Award is a multi-million pound fund that helps to build communities and transform lives through awarding grants to community and environmental projects across the UK, as part of the Landfill Communities Fund.

End of an era

Our Senior Archaeologist is taking phased retirement, so before he goes he has been asked to reflect on his time with the North York Moors National Park.

Graham Lee – Senior Archaeological Conservation Officer

graham-leeHow do I sum up a career lasting over a quarter of a century in a few paragraphs? It is a strange feeling to have 26 years seemingly flash by so fast.

I started work for the North York Moors National Park in April 1990, having previously worked in the archaeology section of North Yorkshire County Council since the summer of 1983. I had decided many years before that I loved the north of England and had no desire to return to my southern ‘roots’.

Graham had decided many years before that he loved the north of England, whatever the weather ... Copyright - NYMNPA.One of my first tasks with the National Park was the completion of a management survey of one of our large estates, encompassing moorland and large blocks of forestry. This quickly whetted my appetite for the excitement of making new archaeological discoveries – often very subtle earthworks, no more than a handful of centimetres in depth or relief – despite an exceptional tradition of previous high quality archaeological fieldwork in the region. Working solo in large blocks of conifers was a good test of dedication – crawling under the branches of dense stands of conifers searching for vague earthworks mapped in the 1890s – and the steadiness of nerve, when yet another wretched pheasant exploded out of the leafy vegetation where I was just about to step! In recent years the delights of discovery have been broadening thanks to new technology and techniques, especially LiDAR which provides an aerial view through tree and ground-cover vegetation of archaeological remains that were previously hidden or obscured.

If you have a passion for the past, the North York Moors have something for pretty much everyone – enigmatic Neolithic rock art; surviving prehistoric pitted boundaries and avenues; upstanding Bronze Age funerary monuments and field systems; Roman encampments; medieval castles and monasteries…

Human industry is also well represented – from the earliest iron industry through the search for alum into the full-blown “iron rush” of the mid 19th century, the exploitation of coal and jet, and the plentiful local rivers managed to provide motive power for a range of watermills. Research and conservation priorities relating to these local industries finally led to our new HLF Landscape Partnership Scheme, This Exploited Land of Iron. Some 15 or so years in gestation, it is very rewarding to see new generations captured by the excitement of the important remains of our 19th century ironstone industry and the associated development of early railways – although the original scheme for a canal link between Whitby and Pickering would have been a sight to behold and a major tourist attraction if it had ever been built.

Into the 20th century, remains survive here from both world wars – in the form of coastal defences, army camps as well as troop training and target practice areas. Finds are still occasionally made of 2nd World War unexploded ordnance in former training areas across the North York Moors, in particular after the wildfire on Fylingdales Moor in 2003 which affected two square kilometres of heather moorland.

Fylingdales Moor after teh wildfire in 2003. Copyright - NYMNPA.

Although an environmental disaster – the severity of the fire in reducing the shallow peat cover to ash, this event was an archaeological revelation. Virtually everywhere you looked, subtle archaeological remains became visible, including the drip gulleys around former prehistoric round houses, low stony prehistoric boundaries and cairns, large numbers of previously unrecorded examples of Neolithic rock art and occasional shallow trenches which resembled grave cuts with a subsiding infill. As numbers of the latter quickly increased their interpretation became clear – slit trenches from 2nd World War troop training. I remember my first visit to the site after the fire when the ground was reddened and blackened, covered in ash and still smouldering; few trees had survived and many had toppled after the peat holding their roots in place had been burnt away. Flashes of colour were very noticeable, such as an adder emerging from its underground refuge having survived the conflagration. A major project ensued, both to protect and restore the moorland habitat and to record and investigate the breath-taking remains of surviving archaeology.

Rosedale Calcining Kilns in a perilous state. Copyright - NYMNPA.There have always been new specialisms to get to grips with. A visit to the Scheduled Rosedale iron calcining kilns with the Park’s Conservation Director at the time revealed that a portion of one of the kilns’ firebrick linings had collapsed the previous winter. This led to a major conservation project to stabilise these huge monuments which ran for three years in the mid 1990s, a forerunner of This Exploited Land which will continue the efforts to conserve these monumental sites 20 years on.

Conservation project to stabalise the Calcining Kilns in the 1990s. Copyright - NYMNPA.

It has been such a pleasure working with like-minded and dedicated professionals, both in my own National Park, but also with colleagues throughout the family of British National Parks, and Historic England and Natural England. We’ve shared experiences and ideas to the betterment of our discipline from research to management, and also shared the excitement of attempting to bring our subject, which we love, to life for anyone who cares to see and to get involved.

Graham at work - examining finds at an archaeological excavation - Coxwold Creative Minds Project, March 2006. Copyright - NYMNPA.

The National Park Authority is currently looking for a new Senior Archaeologist to lead on archaeology in the North York Moors. The closing date for applications is 26 January 2017.

Discovered by Disaster

Aside

Prehistoric ‘cup and ring’ rock on Fylingdales Moor - photo by Jen Heathcote.

Fylingdales Moor on the eastern edge of the North York Moors features in an Historic England blog post from July on archaeological discoveries that came to light due to environmental change. In the case of Fylingdales Moor it was a severe wild fire which was devastating to the natural environment at the time – but from an archaeological point of view every cloud has a silver lining …

via Discovered by Disaster: 6 Astounding Archaeological Finds from Environmental Change — Heritage Calling

Carry on saving the mussels

Simon Hirst – River Esk Project Officer

Our work to safeguard Yorkshire’s last remaining population of Freshwater pearl mussels has received a £300,000 grant from Biffa Award. The River Esk in the north of the National Park is the only river in Yorkshire which still has a Freshwater pearl mussel Margaritifera margaritifera population. The population is estimated to be approximately 1,000 individuals and is in drastic decline. Pollution and sediment build up, decline in fish populations and habitat degradation are all reasons for this.

River Esk Freshwater Pearl Mussel ~40 year old - NYMNPA

The grant received is part of a larger £1.5 million Biffa Award project (2015 – 2018) led by the Freshwater Biological Association that will also see river restoration carried out in river catchments in Cumbria and Devon where freshwater pearl mussels also survive.

One of the key elements of the project will be sharing knowledge and best practice with landowners, the local community and other conservation groups to help give the mussels a more sustainable future. The project will work with farmers to reduce sediment and nutrient input into the Esk, and volunteer groups and angling clubs will be involved in monitoring work such as sampling invertebrate life throughout the river and also restoration work such as planting trees along the river bank and tackling non-native invasive species. The funding will also help sponsor a Master of Research degree at Durham University, which will look at water quality throughout the catchment.

On top of this local effort, the national project will focus on improving the reproductive success of the Freshwater pearl mussel through the Freshwater Biological Association’s captive breeding programme. In 2007, mussels from the Esk were taken to an ‘ark’ facility in the Lake District which houses and breeds populations from threatened Freshwater pearl mussel rivers in England. We’re aiming for sections of the Esk to have been restored enough by 2018 to provide suitable habitat to accommodate the return of the juvenile mussels.

This is a brilliant opportunity for people from different backgrounds to get involved in the conservation of a rare and valuable species. They may not be cute and cuddly but freshwater pearl mussels are an important indicator species; if we get conditions right for them, it will have positive knock on benefits for a range of other wildlife such as otters, Atlantic salmon, dippers and kingfishers.

BiffaBiffa Award is a multi-million pound fund that helps to build communities and transform lives through awarding grants to community and environmental projects across the UK, as part of the Landfill Communities Fund. More information on the award is available at www.biffa-award.org.

Juvenile mussel at captive breeding facility - copyight Louise Lavictoire FBA

River Esk research work - NYMNPA

Encystement project - NYMNPA

This new project which started in March builds on the WREN funded three year Freshwater Pearl Mussel project which finished in February.  This project had similar aims to the new project – to educate and involve people, and to carry out restoration work to limit nutrient and silt input into watercourses which damages spawning gravels and juvenile mussel habitats.

WREN Project Outputs

WREN FWPM Project - river bank fencing - NYMNPAWREN FWPM Project - river bank fencing - NYMNPA WREN FWPM Project - river bank fencing - NYMNPA

 

 

WREN FWPM Project - bank stabilisation - NYMNPAWREN FWPM Project - crossing point - NYMNPAWREN FWPM Project - buffer strip - NYMNPA

 

 

 

 

WREN FWPM Project - tree planting - NYMNPAWREN FWPM Project - trough installation - NYMNPA WREN FWPM Project - tree planting - NYMNPA

 

WREN FWPM Project - river bank fencing - NYMNPAWREN FWPM Project - new cattle watering point - NYMNPA
WREN FWPM Project - gateway improvement - NYMNPA

 

 

WREN FWPM Project - Himalayn balsam control - River Esk Volunteers Task - NYMNPA

As well as nutrient and sediment free water the best habitat for Freshwater pearl mussels is a boulder stabilised substrate with pockets of coarse sand and gravel for burrowing. Water quality monitoring equipment was installed at the key potential re-introduction site on the Esk to measure a variety of water quality parameters such as dissolved oxygen, nitrogen and pH. Redox surveys were carried out to assess juvenile pearl mussel habitat quality – redox surveys measure the water quality within the river gravels (where the young mussels live). One of the Esk sites which was surveyed had redox readings which were potentially suitable for young mussels (which is really positive news), and a few other sites are very close to being suitable.

logoWREN is a not-for-profit business that helps benefit the lives of people who live close to landfill sites by awarding grants for community, biodiversity and heritage projects.

 

Potential FWPM re-introduction site on River Esk - NYMNPAThis is a long term effort. By 2018 all the work and funding over the last 10 years will hopefully come to fruition and the Freshwater pearl mussel will have a sustainable future in the River Esk.