Atlantic salmon (Salmo salar).
Clean, well oxygenated rivers with an unobstructed route from the sea to the higher parts of the river catchment. Salmon also need areas of gravel on the river bed in which to lay their eggs.
Adult salmon in the sea look sleek and silver and can reach over one metre in length. Salmon returning to rivers to breed have survived a long and hard journey, and they are thinner with pink and red blotches. Young salmon in rivers are up to about 20cm long, and are silver with small black spots.
The Atlantic salmon has a truly amazing life cycle. Adult salmon breed in clean rivers, usually in November or December. The female uses her tail to scoop out a hollow (called a ‘redd’) in the gravel on the river bed. She lays eggs in the hollow, the male fertilizes them and then the female uses her tail to bury the eggs.
When the baby fish hatch in the spring, they feed on worms and insect larvae. By the time the fish are 2 or 3 years old, they are nearly 20cm long and ready to migrate to the sea. These young salmon – known as smolts – swim down the river, out into the sea, and then make their way hundreds of miles north to the Atlantic Ocean. At sea, salmon feed on a variety of food including skrill (small shrimp-like animals), small herrings and sand eels.
When the salmon is 3 or 4 years old it is ready to breed, and so finds its way from the Atlantic Ocean right back to the same spot in the river where it hatched – often a journey of hundreds or even thousands of miles. It’s possible that salmon use the earth’s magnetic field or even the stars to help them find their way. When they reach the coastline, they detect chemicals in the water to ‘smell’ their own river.
The journey upstream is very hard work, as they may have to leap rapids, weirs and waterfalls. In November or December, stand on a bridge over the River Esk and, if you are lucky, you might be able to see salmon making their way upstream.
When they reach the place where they hatched, they lay eggs and fertilize them. Many salmon are exhausted after the long journey and die after spawning, but some survive to return to the sea again. After another couple of years at sea they will be bigger and stronger and ready to spawn again. Salmon that have spent two years feeding in the sea can weigh over 10kg and fish of this size can be caught in the River Esk.
The River Esk is one of only a few rivers in Yorkshire that supports salmon. The National Park Authority works with farmers, fishing clubs and local people in order to help improve the river for salmon and other wildlife.
For example, in some places extra gravel has been added to the river to provide better places for salmon to spawn. Elsewhere, obstructions have been removed or fish passes have been built beside weirs to help salmon swimming upstream reach their spawning sites.