The River Exe Project - Salmon in the Classroom

Schools Help Provide Boost to River Exe Salmon Stocks

As part of the River Exe Project, supported by the Exmoor National Park Sustainable Development Fund, Dulverton Middle School, Exford Primary, Uplowman Primary and Blundell’s Preparatory School have been rearing their own River Exe Salmon in their classrooms.

John Hickey, River Exe Project Officer from the Westcountry Rivers Trust, has been running the scheme with schools and undertook the first education visits to the schools last autumn. Through the visits the schools have been learning about the River Exe, its water cycle and its wildlife. As ‘river detectives’ the children investigated the water quality of their local rivers the Haddeo and Lowman. Everyone identified the macro-invertebrates otherwise known as river bugs and beasties, from which they can tell if the rivers have been suffering from pollution. The river detectives were pleased to report that the water quality was good, as attested by the presence of pollution sensitive taxa; the stoneflies, mayflies and freshwater shrimp require clean well oxygenated water and were found in abundance.

On the visit the children saw the gravels where salmon should be spawning successfully. Unfortunately they have been struggling in recent years due to siltation of the spawning gravels in part due to climate change and the heavy downpours of rain which washes soil from farmers’ fields and erodes the riverbanks, leading to the smothering and choking of the eggs. Whilst the project works with the landowners to tackle the problems facing the rivers, in the short term stocking is being used to help enhance the salmon population and the schools have been keen to take part in the project to help boost the salmon stocks.

The salmon in the River Exe spawned mainly in December this year, with the Exebridge hatchery stripping the eggs from the adults up until Christmas. The hatchery held the eggs until early February when the tanks were set up and each school received one hundred eggs for rearing on.

Salmon eggs take roughly an accumulated 450 degrees of temperature days to hatch out. Therefore at a water temperature of 10 degrees Celsius they would take 45 days to hatch. Salmon eggs need to be kept in cool well oxygenated water at a temperature below 12 degrees otherwise they will die. These are the perfect conditions found high up on Exmoor for the early development of the eggs. In schools tanks are set up in the classrooms with coolers so that the water temperature could be kept at a similar temperature to the river. This winter the water temperature was again very cold. The arrival of snow in the New Year kept the water temperature below 4 degrees for several weeks. The eggs hatched out at the end of February and at this stage the alevins have a clearly visible yolk sac attached on the underside of their body, which provides them with all the nourishment that they require to develop. Therefore the alevins do not need to feed at this stage and dive down into the gravels. They will remain hidden away in the gravels for up to a month to avoid predators and the strong currents whilst they gather their strength, when they will suddenly emerge as swim up fry ready to eagerly start feeding. This stage was reached in the schools tanks at Easter, with the water temperature at 10 degrees it is the ideal temperature for salmonids to feed and quickly grow. However, as the river temperature was still low, (everything seemed to be developing about three weeks late this spring) the fry were held at the hatchery until late May when the rivers were suitable for their release.

The salmon fry were released recently by the children from Dulverton and Exford into the Haddeo in an area of excellent habitat, which will offer them the best chance of survival. The fry are only about 3-4 centimetres long but each fish is independent now and will begin the fight for life to find enough space in the stream to provide shelter between the stones and provide it with a good food supply to allow it to strongly grow and develop into parr. Hopefully after two years in the nursery streams the juvenile salmon parr will have reached about 12-15 centimetres in length and they will smolt and then emigrate to sea in the spring, to begin the migration to the rich feeding grounds off Greenland. This marine phase may last for two years before they then return to complete the breeding cycle in the very areas where they were released four years previously.

Commenting on the successful project, John Hickey said: “We would like to thank all the project funders, particularly Exmoor National Park Sustainable Development Fund and the River Exe and Tributaries Association for making the project a reality.”