A fishy tale
Assistant Landscape Architect Sian Rossiter spent a day at the Salmon Trap on the River Dee, which is a short stroll from our office.
Operated by Natural Resources Wales, the trap was built in 1991 to monitor the movement of salmon and trout along the 70-mile-long River Dee.
The Dee is one of a few ‘index’ monitored rivers for Atlantic Salmon and Sea trout in Europe and is the only index river in Wales. These are characterised by their intensive and long-term monitoring programmes collecting unique information on the key life stages of these important fish.
Sian said: “If you stand on the Old Dee Bridge in Chester and look upstream you can spot an ugly box of a building positioned at the top of the salmon ladder.
“I was fortunate to visit the trap recently to see it in operation and to learn how the work being undertaking here is helping scientists to better understand migratory species.
“Atlantic salmon, along with other migratory species, are critically endangered which means that the work in tagging, tracking, and monitoring such species in the Welsh Dee is vitally important.
“Salmon numbers in the Dee have declined substantially since monitoring commenced in 1991 whereby the estimated salmon run in 1991 was approximately 6,000 fish. In 2022, the number had dropped to under the 3,000 mark which is clearly a massive cause for concern. Sea trout numbers in the appear to have dipped to about 11,000 over the last few years.
“During my visit there were about 50 fish in the trap – ten salmon and 40 sea trout. The largest salmon tagged was 12lbs while the largest sea trout came in at 8lbs. For this time of the year, that’s a typical catch although salmon numbers are expected to increase as the main migration gets under way in September.
“It was good to get a better understanding of the plight of these important migratory species and the key factors which are affecting their long-term survival.”
These include:
River pollution and silting of important gravel beds for spawning.
River obstructions – dams and weirs which prevent migratory passage up the river.
Invasive species – American signal crayfish and Chinese mitten crabs have been found in the Dee and they are currently colonising areas as they move up the dee catchment. Pink salmon is a newcomer which originate as escapees from fish farms in Norway and Russia. Pink salmon are a particular concern as not only do they compete with the native Atlantic salmon for habitat, there is also a danger of hybridisation taking place.
By-Catch – Salmon smolts (young salmon) are sometimes caught by accident by fishing boats targeting other species.
Disease - Salmon are particularly affected by a parasite called Gyrodactylus salaris.
Fish Farming - Causing high concentrations of sea lice, pollution of the environment by uneaten food, fish faeces or medications used to treat salmon in their cages.
Climate change – River temperatures increasing slightly and falling outside the preferred salmon and trout range can be lethal. In addition to this, with the Artic ice cap contracting salmon are needing to travel much further to feed resulting in many spending more time at sea then they would normally have done so.