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.

3 thoughts on “Increasing life chances – Part 2

  1. There seems to be a ‘fashion’ amongst conservationists for sediment control, using such methods as tree planting, stabilising banks, fencing the river from stock, buffer strips, etc., yet in every single victorian or edwardian photograph I’ve ever seen of the esk valley there were far less trees, and very few in or on river banks, because stock had access to all the river and streams. Thirty years ago or more there were far more crops grown in the Esk catchment area, ploughed fields were generally left fallow all winter before planting spring crops and all this of course produced much, more sediment run off. And yet salmon and we must presume, the pearl mussel, thrived. They also thrived in the face of run off from ironstone, jet mines, quarries, alum extraction, some of which must have produced vast amounts of sediment and certainly more than is the case now.

    Have you any evidence that sedimentation has increased or is a genuine problem in modern times?

  2. We have carried out monitoring of the Esk river bed and gravels using a redox probe. This redox monitoring allows us to understand how well oxygenated the river gravels are (as sediment smothers the river bed, the spaces between the river gravels become blocked and clean water cannot pass through). Clean river gravels are critical habitats for the juvenile mussels, as they live buried in the river gravels (up to 10 cm deep). Our redox monitoring has shown the gravels have too much sediment currently for survival of the juvenile pearl mussels. This is why we are trying to address sources of sediment in the catchment (along with other works to improve water quality, remove barriers to fish migration and restore river habitats).

    Simon Hirst
    River Esk Project Officer

  3. Pingback: A to Z – starting, unsurprisingly, with A | The official blog for the North York Moors National Park

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