What does it mean to restore Atlantic salmon, a keystone species, to the Don catchment?

So now that we’re starting to see signs of salmon returning to the Don catchment after 200 years of being absent, what value will this bring to the area aside from the intrinsic value of restoring species back to their natural home?

Salmon are considered to be a keystone species – much like beavers. A keystone species is one that has a disproportionate effect on the ecosystem relative to its proportion and is considered an essential element to the healthy functioning of their native environment. Without keystone species the ecosystem would be completely different or not exist at all.

Every stage of a salmon’s lifecycle has a significant effect to their surrounding environment which is the reason why they are considered a keystone species. After two years at sea foraging in the Atlantic Ocean, the nutrients which they have gained can have them growing to around 74 cm in length and 4.5kg in weight. Those nutrients are then brought back upstream and then distributed along the river habitat and beyond.

Atlantic Salmon (Salmo Salar) Being released in from a tagging, River Tamar, Cornwall. Photo credit – Jack Perks

Their eggs are food for foraging dippers or other fish looking for a quick meal during the winter months when food is scares. As young, alvein and smolts are food for predatory fish such as trout and pike as well as birds which prey on fish such as goosander and heron whilst not forgetting ospreys as they perform unthinkable displays of mechanics plucking whole fish (up to 300g) out of the water. On their journey to and from our rivers, salmon are preyed upon by marine animals such as whales, dolphins and seals to name a few. If they haven’t been snatched by a hungry otter first, when they finally return to their natal hatching grounds, most Atlantic salmon will die after spawning and their bodies will be broken down and recycled back into the ecosystem by aquatic and terrestrial invertebrates. Furthermore, whilst we may not have bears in the UK anymore to carry carcasses into the forests as they do in North America (providing trees with a boost of the nitrogen they need to grow), we do have scavengers such as foxes who may be lucky enough to have a spent salmon wash up along their local riverbank and drag them to a nearby wood to eat.

Not only do salmon have an enormous effect on the ecosystem, they also have an impact on the culture and economy to the places they are present. Highly prized by fly anglers, those wishing to hook the “king of fish” will often travel to Scotland where the salmon runs are most well-known.

What other things will it mean to have salmon back to the Don catchment after their long absence? We will have to wait to see!