Waste Not Want Not: Deer Legs in the Muick
This month we hear about an unusual trial to boost nutrient levels in one of the Dee’s upland tributaries.
An unconventional experiment that aims to provide a nutrient boost to one of the Dee’s upland tributaries is underway in the River Muick. In a pioneering 3-year trial, deer legs have been secured in the river to provide an additional source of phosphorus, which is hoped to have a positive effect on the river’s ecosystem.
The project is a collaboration between the River Dee Trust, the James Hutton Institute and the Dee District Salmon Fishery Board (DDSFB), with support from the Balmoral and Glen Muick Estates. River Operations Manager for the DDSFB, Edwin Third, had the arduous task of hammering the deer legs into the river. He explains the reasons behind the trial:
“The Muick’s granite geology means that it is naturally low in nutrients. But once a year the whole river system should receive an important boost, in the form of the carcasses of salmon that die after spawning. Over the years, a steep decline in the river’s salmon population, combined with changing land use, have rendered certain stretches of the Muick very poor in nutrients.” he explains. “After spawning, the carcasses once fed the next generation, but with the reduced fish numbers we’re seeing a marked decline in the overall health of the river. Fewer fish is not just bad news for the economy, but detrimental to entire ecosystems.”
A free waste product sourced from the local estate, the idea for the deer legs came about as a result of another salmon carcass substitute being used elsewhere, as Edwin continues: “Salmon feed pellets were being used in the River Conon to great effect - they observed a doubling of the salmon biomass and a trebling of the invertebrate biomass with the addition of the pellets. But one of the sites had to be abandoned because a deer had fallen into the river nearby and the corresponding measurements for salmon and biomass were off the scale! So we’re pretty sure this will work, but to what extent remains to be seen.”
It’s a delicate balancing act however, as Edwin explains: “We don’t want to over-enrich these tributaries, we just want to help resume some sort of natural equilibrium whereby there are enough nutrients to boost life, with the salmon going out to sea fitter and healthier. If they survive better at sea they’ll return to their spawning grounds in higher numbers and will then restart that cycle themselves. We’re simply trying to create a substitute until that natural process kicks in again.”
Scientists from the James Hutton Institute will monitor the 300-square-metre sites throughout the lifetime of the trial, which will run for another two years. The Hutton’s Catchment Scientist and Manager for the Dee Catchment Partnership, Susan Cooksley, explains:
“Of the 16 sites on the Muick, four of them are control sites without any deer legs, a further four have a high density of deer legs, another four have a lower density, and the last four have only salmon feed pellets. From the algal growth and insect populations in the river downstream, we should be able to tell quite quickly whether the phosphorus – the key element that provides the nutrients the salmon need – has an impact. But how many legs are equivalent to one salmon carcass, we don’t yet know - that’s what we hope to find out.”
“We will be studying the effect that the trial has on the insect populations very carefully to ensure that the delicate natural balance isn’t upset.” Susan continues. “Insect larvae are far more than just fish food, they are extremely important in their own right, and we are lucky to have some very special species present in the tributaries of the Dee, so understanding how they are affected is essential.”
The project has attracted significant media interest, having already featured on Countryfile, and in several national newspapers and magazines. But Edwin is keen to emphasise that this unusual nutrient enhancement trial is just one small strand of an overarching strategy to restore a thriving salmon population:
“The main solution will come from planting riparian woodlands on the upper tributaries – trees really can do everything. They increase the nutrient levels, food supply and the overall complexity of the river, but most importantly they provide shade to keep the river cool during periods of high temperature like those we had last year. We’ve already planted 140,000 trees in the uplands and are committed to planting tens of thousands more in the coming years.”
Suggested photo caption:
Edwin Third, the Dee District Salmon Fishery Board’s River Operations Manager, secures deer legs into the River Muick, in an unusual trial to boost the river’s nutrient levels.
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