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.
Do 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.