In Extremis update

From Eloy at the Freshwater Biological Association Facility:

The Esk mussels are settling in. They are buried and stable, not moving that much, as if they had found their space in the cage.

Recently translocated mussels from the Esk now at the FBA Facility - copyright FBA


In Extremis

Simon Hirst – River Esk Project Officer

As mentioned before on this Blog, the River Esk in the North York Moors is the only river in Yorkshire with a Freshwater pearl mussel (Margaritifera margaritifera) population. Our population is in drastic decline – currently it is estimated there are approximately 1,000 individuals, all adults.

We’re part of a national project (funded by Biffa Award) to conserve the populations of Freshwater pearl mussel in England. Nine years ago a number of the adult mussels were collected from the Esk and moved to the Freshwater Biological Association’s Facility in the Lake District. A couple of weeks ago, early one morning, Eloy from the Association and I collected another 20 and took them across to join the others at the Facility 130 miles away.

Eloy preparing the FPM transportation unit ie a cool box - copyright Simon Hirst, NYMNPA

River Esk substrate to take to the FBA Facility - home comforts for the Esk mussels - copyright Simon Hirst, NYMNPAThe lid of the cool box had to be left open so oxygen exchange could occur during the 3 hour journey - so the box was thoroughly jammed in - copyright Simon Hirst, NYMNPA

Safely arrived at the FBA Facility - acclimatising the Esk mussels to their new home - copyright Simon Hirst, NYMNPAThe idea is the translocated adults breed and the Facility then rear the captive juvenile mussels with the ultimate idea of reintroducing the young mussels back into their native rivers. In the meantime we’re continuing to tackle the problems that have had and continue to have such a detrimental effect on the mussels. So on the Esk we’re working in partnership to improve the riparian habitat in order to increase water quality and vitally reduce the amount of suffocating sediment so that the river becomes a suitable release site and juvenile mussels have a chance of surviving. Improving the river habitat also benefits the migratory fish which are such a vital part of the mussels’ lifecycle.

We’re trying everything we can to help the Esk population and give it the best chance of survival. Mussels can live to be over 100 but if there are no juveniles, slowly but surely the Freshwater pearl mussel will become locally extinct.


Operation Luzula

Kate Bailey – Conservation Graduate Trainee

Since starting as the Conservation Graduate Trainee last September, I have had lots of opportunities to get out and about with our hardworking National Park Volunteers undertaking practical conservation tasks across the National Park.

Last week, I joined the River Esk Volunteers for a day planting woodrush along the banks of the River Esk. Greater woodrush Luzula sylvatica is a native, perennial member of the rush family which grows in damp shady places. It thrives along river banks in the North York Moors, where it grows in tussocks providing great ground cover which helps stabilise the river bank.

A good example of Luzula sylvatica growing along the River Esk - copyright NYMNPA

However there are sites along the River Esk where the banks are void of any vegetation. When stock have access to the river, any natural regeneration gets nibbled off and the river banks are left bare and susceptible to erosion leading to sediment entering the water and choking the river habitat. Woodrush planting coupled with river side fencing to exclude stock and create a bankside buffer strip is potentially one of the solutions to this problem.

Planting woodrush as a means of stabilising the river bank has not been carried out before in the National Park. Simon, our River Esk Project Officer, identified a trial site which could benefit greatly from some conservation effort. The river was fenced off over winter, excluding stock from the damaged river banks and young trees – Hazel and Oak Luzula sylvatica being grown at Mires Beck Nursery– were planted. Last summer National Park Volunteers had helped collect woodrush seeds from other sites along the River Esk (to maintain the local provenance) which were then sent off to the Mires Beck Nursey near Hull. The Nursery primarily produces wildflowers for conservation projects whilst providing opportunities for people with learning difficulties to get involved with horticulture. Our woodrush seeds spent the last eight months being grown on and cared for by the knowledgeable staff and volunteers at Mires Beck Nursery. The plants were delivered back to the North York Moors last week, ready to be planted.

Woodrush planting task - copyright NYMNPA

It was an extremely well attended planting task for a Monday in March – and it was sunny. The River Esk Volunteers were joined by three members of staff from Mires Beck Nursery who made the journey up from Hull to deliver the 3600 woodrush plants. Hopefully the newly planted woodrush will flourish and the river banks will be covered in vegetation once more, safeguarding the River Esk habitat and all its associated species.

Planted woodrush on the banks of the River Esk - copyright NYMNPA

Woodrush planting is one element of the Esk Pearl Mussel and Salmon Recovery Project which is working to sustain Yorkshire’s last remaining population of Freshwater pearl mussels Margaritifera margaritifera. The River Esk Project has been boosted with a £300,000 grant from Biffa Award. The grant forms part of a larger £1.5 million Biffa Award project led by the Freshwater Biological Association that involves river restoration in a number of Freshwater Pearl Mussel catchments in the country, including in Cumbria and Devon, as well as Yorkshire. “This project is an exciting opportunity to save one of the most long-lived animals from extinction; the freshwater pearl mussel can live for more than 100 years and is internationally protected” – Gillian French, Biffa Award Programme Manager,

Biffa Award logo

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. More information on the award is available at

A to Z – starting, unsurprisingly, with A

We thought we’d try something new, new for us anyway. Now and again we’re going to post bits and pieces on conservation. the National Park and the North York Moors – under each letter of the alphabet. That’s the plan – we’ll see how far we get.



The North York Moors includes large areas of forest owned and/or managed by the Forestry Commission. These forests were planted at the beginning of the 20th century when in a time of uncertainty following World War One it was decided that the nation needed to create and maintain its own timber resource. This afforestation had a dramatic long term effect on the landscape of the North York Moors which continues today. Timber and other wood products from both public and private enterprises in the National Park remain economically important to the North York Moors.

Boltby Forest - Southwoods - NYMNPA

Boltby Forest - Southwoods - NYMNPA

This is using the word afforestation as it is understood nowadays – turning land into forest by planting trees. In medieval times afforestation meant designating land as forest and therefore placing it under forest law, separate from common law. A forest meant an area for hunting belonging to the Crown; so heathland and grassland as well as woodland, wherever deer and boar and other game animals would live.

ALCATHOE BAT Myotis alcathoe

This bat was first identified as being in the United Kingdom in 2010 – in Sussex and in the North York Moors. It could have been here for years it’s just that it’s difficult to distinguish from other bat species. The Alcathoe bat lives in woodland and swarms with other bats to mate before hibernation. One of the records in the North York Moors was from the autumn swarming at one of the Ryedale Windy Pits.

Alcathoe bat. From


Alum was one of England’s earliest chemical industries, operating in the North East Yorkshire region from c.1604 until 1871. Alum (aluminium sulphate) was important in textile production which was our main export in the 17th century, and was used as a compound with potassium (e.g. seaweed) and ammonia (e.g. urine – at first collected locally and later also shipped in from coastal towns) to make vegetable dyes colour-fast. With the exception of one Alum Works in Lancashire, North East Yorkshire produced the entire supply of English alum until the early years of the 19th century. The main Alum Works and Quarries were along the coast, which provided better exposures of the mineral together with the most practical means of transport to markets when travelling by sea was a much better prospect then setting off across country. Although softened by over a century of weathering and coastal erosion, the extracting and processing industry has left huge imprints on the North York Moors landscapes which can still be seen today for example at Ravenscar, Saltwick, and Kettleness.

Saltwick Nab Alum Works - NYMNPA Saltwick Nab Alum Works - NYMNPASaltwick Nab Alum Works - NYMNPA

Saltwick Nab Alum Works - NYMNPASaltwick Nab Alum Works - NYMNPASaltwick Nab Alum Works - NYMNPA

(WILD) ARUM (Arum maculatum)

Also known as Lords and Ladies, Cuckoo Pint etc.

Grows on hedge banks and on woodland edges in the leaf enriched soil. Common throughout Britain and Ireland.

Looks like something from science fiction and has a life cycle to suit.

Has large shiny green leaves sometimes with dark blotches, followed by a thin leaf like cowl growing up through the centre and partially opening to reveal a smelly purple-ish central spike (March/April). This smelly heat emitting spike attracts insects which then slip down into the plant and are temporarily trapped in the base where they pollinate the tiny hidden flowers (female) and collect pollen from the male flowers to carry elsewhere once released. The leaves and initial spike wither away and are replaced by another spike growing upwards topped with the female flowers as small berries which turn from green to red (July/August). Birds eat the berries – but they’re unpalatable and poisonous to humans, as is most of the plant.

Wild Arum. From Arum. From


The Esk is the principal Atlantic salmon river in Yorkshire. The whole of the River Esk catchment is within the North York Moor National Park.

The rod catch on the Esk in 1923 was 950 fish per year, this number has declined to about 170 fish in 2010. The National Park Authority’s Esk Pearl Mussel and Salmon Recovery Project has been running since 2007 and its aims include reversing the decline in the Atlantic salmon population in the river by improving water quality, improving in-river and riparian habitats and removing barriers to vital fish migration.

Atlantic salmon. From - picture by Thomas Kitchin & Victoria Hurst


i.e. the right attitude to work positively with people in the National Park to listen to what others have to say; to try and tackle concerns; and to take forward National Park purposes together.

The latest example of this attitude in action has been the Dales and Moors Farm Innovation Pilot Project where the North York Moors National Park worked with the Yorkshire Dales National Park and neighbouring Areas of Outstanding Beauty across the wider area and used skills funding through the local LEP to provide free business and environmental advice to guide local farmers into producing their own whole farm plans and tailored proposals for sustainable ways forward for their farms.


White-clawed crayfish - Helen Webster, NYMNPAAustropotamobius pallipes are native White-clawed crayfish. The upper tributaries of the
Yorkshire River Derwent in the National Park still support populations of this nationally declining species. What with needing clean aquatic habitats, competing with non-native aggressive signal crayfish, and suffering from deadly crayfish plague, the White-clawed crayfish are in a perilous situation. Just when you thought their luck couldn’t get any worse, one of these Yorkshire Derwent tributaries, the River Rye, tends to dry out in the summer at one particular location because of sink holes, leaving the local population of White-clawed crayfish and other aquatic creatures stranded.

So just like a year ago, last week we had to launch another rescue mission. Alex led a team of Emily, Simon (who has a licence to trap and/or remove crayfish), Helen the Planning Officer, Alex’s partner Toby, and a helpful man called Jim and his dog. They managed to collect and relocate upstream of the sink holes around 500 White-clawed crayfish (including females carrying hatchlings) as well as 20+ lamprey and 40+ small fish that were scooped up with them.

River Rye crayfish rescue 16 7 15 - Alex Cripps, NYMNPARiver Rye crayfish rescue 16 7 15 - Helen Webster, NYMNPA







River Rye crayfish rescue 16 7 15 - Helen Webster, NYMNPARiver Rye crayfish rescue 16 7 15 - Helen Webster, NYMNPA









River Rye crayfish rescue 16 7 15 - Alex Cripps, NYMNPA

River Rye crayfish rescue 16 7 15 - if you look closely you might make out the hatchlings on the abdomen - Alex Cripps, NYMNPAA couple of weeks before the Environment Agency (EA) had carried out a fish rescue at the same location. The EA rescued and re-located 265 Brown Trout, 65 Grayling, 5 Lamprey and 100s of minor fish species including minnows, stone loach and bullheads. They also rescued 50 White-clawed crayfish, some carrying eggs.

At the start of life

Simon Hirst – River Esk Project Officer

Salmon in the Classroom May 2015 - NYMNPAAn important part of our work on the River Esk is engaging with local people who are vital in helping to secure a sustainable future for the salmon and trout, and the freshwater pearl mussel population who live in the river. For the past 7 years we’ve been rolling out the Salmon in the Classroom initiative to a different village school each year in the Esk Catchment. This year it’s been the turn of Goathland Primary School.

We supplied the hatchery tank and the Atlantic Salmon eggs in Salmon in the Classroom May 2015 - NYMNPAMarch and the children have been raising the fish since then through the initial stage of their life cycle (from egg to fry). At the same time Heather and trainee teachers Megan and Francesca from our Education Team have been telling the children the story of the creatures who live together in the river including the illusive pearl mussels whose larvae rely on the fish as hosts, and illustrating the value of the children’s local river environment. The children have had the rare chance to see the start of life for the fish in front of their eyes, and in return have produced inspired artwork.

Salmon in the Classroom May 2015 - NYMNPAA couple of weeks ago the children released the young fish – around 70 of them – into the Murk Esk at Beck Hole. The released fish will remain in the river for around two years – growing and developing until they are big enough to migrate out to sea. Then hopefully they’ll return to the Esk river network in about three years’ time to spawn and produce young of their own.




The fry waiting to be released - Salmon in the Classroom May 2015 - NYMNPAAs mentioned previously, the River Esk is the only river in Yorkshire with a freshwater pearl mussel population but numbers are in drastic decline. With the help of landowners and in partnership with the Yorkshire Esk Rivers Trust (YERT), we’re carrying out restoration work along the river to improve the river habitat for the benefit of the mussels and other river species. Pollution and sediment build up, decline in fish populations and habitat degradation are all recognised reasons for the decline. An improved habitat would allow the re-introduction of juvenile pearl mussels currently being raised through the captive breeding programme at the Freshwater Biological Association facility in Windermere, in order to boost the ageing population hanging on in the Esk.

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!

Electrofishing - May 2015 - NYMNPA

Checking for glochidia - May 2015 - NYMNPAClose up - checking for glochidia - May 2015 - NYMNPASuccesful group shot - May 2015 - NYMNPAAmazingly, 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.

Increasing life chances – Part 2

Emily Collins – Conservation Student Intern

Following on from Increasing life chances – Part 1

Everyone knows that running a 26 mile marathon can be gruelling. Even after months of preparation, the ‘once in a lifetime’ experience is considered to be both mentally and physically challenging. Imagine then, having to travel that same distance year after year, not on land but against a freshwater current, with various obstacles in your way. Impossible?

Well, not if you’re a salmonid.

Salmon and trout literally ‘go the extra mile’ when it comes to ensuring their offspring have a bright start. In the North York Moors, travelling from the mouth of the River Esk at Whitby to as far upstream as Westerdale up in the moors, it seems these aquatic athletes (video) will tackle any challenge in order to spawn at their original birthplaces. They even undergo physiological changes which allow them to swim from saltwater to freshwater habitat.

There are, however, hurdles which fish can’t always surmount. The number of fords and weirs throughout the Esk has meant that many fish find it very difficult to reach their intended destination. When leaping over or squeezing through obstacles, many fish get stuck, damaged or become more vulnerable to predation. As a result, fewer eggs are fertilised upstream and females are forced to spawn where they can often in sub-optimal habitat, leading to an overall decline in the fish population.

Trout jumping from Irish Bridge/Ford - NYMNPADo you remember our old friend the Freshwater Pearl Mussel which we’re especially keen to encourage? Salmon and trout parr remain in the Esk for around a year after hatching and it’s in this time that the baby peal mussels, or glochidia, encyst upon their gills. After nine months the mussels drop into the gravel bed and the fish swim downstream to the mouth of the Esk to smolt. This is a vital part of the mussel’s life cycle so it’s crucial that high salmon and trout numbers are maintained in order to increase the chances of encystment occurring.

We can help salmon and trout to reach their upstream spawning sites by installing fish passes and fish easements through the obstacles. Ramps can be created at weirs and culverts and water levels raised artificially so that fish can swim over the barrier without harming themselves. The tubing underneath fords – in which fish can become trapped – can be replaced by wider, fish-friendly tunnels the fish can swim through.

Fish passes are in place at Ruswarp Weir and Sleights Weir but there are 21 barriers on the Esk and its tributaries and so there is still much work to be done. Gradually we’re hoping to pick up on other sites upstream when opportunities arise. This is all part of the habitat connectivity work underway in the National Park to strengthen landscape corridors for wildlife. Through the upcoming This Exploited Land HLF Landscape Partnership project we’re planning to install fish easements at Glaisdale Beck ford and Butter Beck ford. In the meantime, we are working in partnership with the Yorkshire Esk Rivers Trust (YERT) to reduce sediment and pollution in the Esk and improve the overall river habitat for salmon and trout and in doing so increase their chances, as well as the chances of the Freshwater Pearl Mussel.

Increasing life chances – Part 1

Emily Collins – Conservation Student Intern

Salmon and Trout Lifecycle

When I first arrived at the National Park and learnt about how Freshwater Pearl Mussels in the River Esk depend on salmon and trout (both salmonids) in the early stages of life, I got a little confused. I thought that the mussels remained on the gills when the fish went out to sea and couldn’t understand how the mussels would survive this transition from freshwater to saltwater. It was only when I read about the salmonid life cycle that I realised I was wrong.

Salmon alevins - from

Salmon and trout hatch in the spring as alevins which remain in the gravel and feed off their attached yolk sacs. Once the sac has disappeared they start foraging for food around the hatch-site and are known as fry. Only when they leave that part of the river to defend their own territories are they known as parr – these can be identified by the fingerprint markings on their side.

Parr defend the same area of river for two to five years and it’s at this stage in their lifecycle that they interact with the mussels by hosting them in their gills till the mussels drop off. Once mature, the parr then undergo a process called smolting when they turn a silvery colour, their fins darken and the parr markings disappear. They also undergo changes internally which allow them to adapt to survival in saltwater. Importantly they manage a process called osmoregulation which involves excreting excess salt and guarding against loss of water to maintain a healthy ion balance.

Salmon parr - from

Hormonal changes guide the fish downstream and out to sea where they feed on sand eels, krill, herring and crustaceans. At this point in their lifecycle they grow very rapidly and build up layers of fat in order to store energy for the journey back up the Esk. After one to four years, between April and November, they return to freshwater and take on the challenging counter-current swim to their natal site where they themselves were born.

Salmon - from

This will be the final journey for the majority of the females. All of their energy is invested in producing eggs and reaching the spawning site so that by the time they have dug a hole and released eggs for the male to fertilise, they have very little energy left to make it back to the sea. In fact, just 5-10% of Atlantic Salmon survive their first spawning.

Against all the odds fish do spawn, however we want to shorten the odds and influence the probability.

Team working for the River Esk


This gallery contains 13 photos.

Simon Hirst – River Esk Project Officer The River Esk Volunteer Group was established at the start of the WREN funded “Esk Pearl Mussel Recovery” project and have been going ever since. The aim of the project is to improve … Continue reading

Saving our Pearl Mussels: assisting encystment

Sam Jones – River Esk Project Student

The big day finally arrived. As mentioned previously (at least twice) we have been prepping for our bankside encystment project to assist the endangered Freshwater pearl mussel in the Yorkshire Esk to reproduce. I won’t go into it too much as I think I’ve told you the process in enough detail but suffice it to say all went to plan – without a hitch*. The Environment Agency team were brilliant and we got all the fish we needed in plenty of time, even the weather behaved, and the mussels – well they didn’t really seem to do anything, because they’re mussels – but hopefully they produced their glochidia.

Now we can only wait and see next spring whether we were successful. Hopefully we will be bringing you news of lots of developing young mussels on the fishes’ gills next year.

I’ll leave you a taste of the rather manic day – see the pictures below and there is even an 8 minute feature.

Now unfortunately I must say goodbye. My year of working for the North York Moors National Park Authority has come to an end, and it has been wonderful.



* There was a potential hitch. About a week previously Simon, the Esk Project Officer and lead on the Encystment Project, had dislocated his knee which curtailed his mobility and meant he was unable to be involved on the day. Fortunately Sam stepped up to the task, and Simon is now on the mend.