Boost for River Exe Salmon Stocks

Salmon stocks have received a boost thanks to the efforts of the River Exe Project (with funding from the Exmoor Sustainable Development Fund), Dulverton Middle School and Blundell’s Preparatory School. The project and schools have been rearing their own River Exe Salmon in their classrooms assisted by John Hickey, the River Exe Project Officer from the Westcountry Rivers Trust, who has been running the scheme with the schools since October 2008.

The schools have been learning about the River Exe through visits, 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 which require clean oxygenated water and were found in abundance.

The children saw the gravels where salmon should be spawning successfully. Unfortunately the fish have been struggling in recent years due to siltation of the spawning gravels, partly 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. John Hickey said: “Once they understood the problems, the youngsters were keen to take part in the project to help boost the salmon stocks.”

The salmon on the Exe spawned last December, with the Exebridge hatchery stripping the adults up until Christmas. The hatchery then held the eggs until they reached the ‘eyed’ stage in early February this year. Once the eggs have reached the eyed stage they are far less sensitive to shock and may be moved so each school received one hundred eggs for rearing on.

The fairly cold winter meant that the holding tanks had to be kept at the same level as the temperature of the water in the river as salmon eggs need to be kept in cool, well oxygenated water at a temperature below 12 degrees otherwise they will die. These perfect conditions are found high up on Exmoor for the early development of the eggs.

The eggs hatched out at the end of February and at this stage the young fry, or alevins, had a clearly visible yolk sac attached on the underside of their body, which provides them with all the nourishment that they require to develop. They 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 suddenly emerge as swim up fry ready to eagerly start feeding. John Hickey continued: “The salmon fry were released in areas of excellent habitat which will offer them the best chance of survival. Although they are only about 3 centimetres long, each fish is independent and will begin the fight for life to find enough space in the stream to allow it to strongly grow and develop.

“Hopefully after two years in the nursery streams the juvenile salmon 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.

“I’d like to say thank-you to all project funders particularly the River Exe and Tributaries Association and the Exmoor National Park Sustainable Development Fund for making the project a reality.”