European Eel

The European eel population was thriving until the 1980s and, although slowly recovering, numbers arriving in Europe have fallen by around 95%. This is due to loss of habitat and access, overfishing, climate change and disease. It is now on the critically endangered list.

European eels are catadromous fish, meaning they live their whole adult lives in freshwater rivers and streams, but migrate back to the sea to spawn. They have been known to live up to 20 years in the wild and have reached 50-80 years old in captivity.

The life cycle of a European eel

• They travel over 4,000 miles from the River Stour to lay their eggs in the depths of the Sargasso Sea near Bermuda
• The adult eels die after spawning, but the eggs hatch into larvae called ‘leptocephalus’ which the Gulf Stream then carries back across the Atlantic. This process can take 300 days
• When they arrive near the coast, the larvae metamorphose into a transparent larval stage called ‘glass eels’
• They swim into the river estuaries, before making their way up to the rivers themselves. At this stage, they become much darker and are known as ‘elvers’ which are miniature versions of the adult eels
• As they continue to journey up-river, they feed voraciously on invertebrates and even other fish. They grow as they begin to take on the adult form and are known as ‘yellow eels’
• After five to twenty years spent in fresh or brackish water, they become sexually mature. Their eyes grow larger and they change colour. Their flanks turn silver and their bellies become white. At this stage they are known as ‘silver eels’ and they begin their migration back to the sea to repeat the journey that their parents had made before them.

Atlantic Salmon

Salmon are anadromous fish, meaning they live most of their adult lives in the sea but migrate back to freshwater rivers and streams to spawn. You can find salmon that have migrated from the Atlantic Ocean, as well as juvenile salmon known as ‘parr’, in the lower reaches of the Stour around the South Staffordshire/ Worcestershire area.

Salmon always return to the very same river to breed and lay their eggs in the exact spot that they themselves were spawned. This is a miraculous undertaking and how they find their way back remains a mystery.

Some studies suggest that they use the earth’s magnetic field to find their natal river, others indicate that the salmon use their strong sense of smell to locate the river of their birth.

The life cycle of an Atlantic salmon

• The Atlantic salmon starts life as a fertilised egg laid in suitable gravels in late autumn within well oxygenated water, free of silt
• In early spring, the eggs hatch into tiny larvae known as ‘alevins’ which still have their yolk attached to them
• They emerge from the gravel after three to four weeks ready to feed as fully developed ‘fry’
• By the end of the summer as they feed and grow, they become known as ‘parr’. They remain in the river for between one and three years feeding on invertebrates
• ‘Parr’ salmon then become ‘smolts’ in the spring of their second, third or fourth year of life
• They migrate to the sea in April, May or June where they spend one or two years in the North Atlantic, often in areas off Greenland and Iceland feeding on fish such as sand eels, herring and plankton
• Their journey back to their natal rivers then begins, and they typically start returning up-river in spring where they are known as ‘grilse’

Artificial barriers such as weirs make their migration far more difficult. Returning salmon do not feed whilst in freshwater and use all their built-up energy reserves from one or two years spent feeding at sea to migrate back upriver to their spawning gravels.

Although they can leap vertically up to 12ft high if the water is deep enough for them to propel themselves out of, having to jump over countless obstacles uses up valuable energy needed for spawning. This means that salmon can sometimes be spent, or very weak, even before they have had time to breed successfully. This reduces the numbers of eggs that are laid and fertilised, and results in fewer fry and juveniles needed for sustaining the species into the future.

After spawning around 90% of the adult salmon die. A small number survive to make their way back to sea for another year or two, before returning to their original rivers again to spawn.

Within the river

Species including brown trout and coarse fish spend their whole lives in freshwater, but they still need adequate conditions and a suitable breeding habitat to spawn. They can undertake localised migrations within the River Stour or even between rivers. Sea trout migrate back to the rivers to breed, just like Atlantic salmon.

Brown trout prefer fast-flowing rivers. Females lay their eggs in suitable gravels and the young newly hatched trout are known are as ‘fry’.  

Within the River Stour there are numerous, very common fish called bullheads which also have very interesting life cycles. It is the only freshwater fish in Britain which is a member of the sculpin family, which is comprised mostly of marine species. They breed between February and June and the males excavate a nest under a suitably large stone where the female can lay up to 400 eggs.

The male then guards the developing brood and fans oxygenated water over the eggs with his pectoral fins until they hatch after 20 or 30 days, depending on water temperature. The male bullhead thus carries out most of the parenting duties.

Although they don’t make the long journeys that European eels and Atlantic salmon do, conditions such as water quality still need to be adequate for the species to thrive.

Threats to fish in the River Stour

The River Stour played a vital role in the region’s industrial heritage, but the heavy modifications made to the river have resulted in long-term habitat damage. Manmade barriers such as weirs and dams remain in place, preventing fish species from accessing suitable places to spawn. Whole stretches of river can be devoid of certain fish species, who cannot access them due to the barriers which still remain in place.

More recently, poor water quality, litter and invasive species have made parts of the Stour unsuitable.  Our Love Your River Stour project is another step towards improving the river for the wildlife that lives in, on, and alongside it, whilst also making the surrounding green spaces become  more accessible for everyone to enjoy.