Rare fish returns to River Don

A rare and protected sea lamprey.

A rare and protected sea lamprey.

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A rare and protected fish has been caught in the River Don for the first time in recent history as water quality in the region’s rivers continues to improve.

Two sea lamprey were caught during an Environment Agency fish survey on the River Don at Crimpsall, Doncaster.

Lampreys are an ancient group of eel-like jawless fish that have lived on earth largely unchanged for 300 million years – appearing about 70 million years before the first dinosaur.

The young live in rivers before migrating to the sea. At sea, they use their suction-cup like mouths to attach themselves to the skin of fish, rasping away tissue with their sharp probing tongues and teeth. Adult sea lamprey return to rivers to spawn.

These fish are a good indication of the high quality of the river water. Breeding populations occur in North Yorkshire and scientists are currently trying to track down their spawning grounds.

Environment Agency monitoring officers were using an electric fishing technique when they came across the sea lamprey. They pass an electric current through the water to temporarily stun the fish so they can be counted, measured and then released unharmed.

Darren Rollins, Environment Agency monitoring officer, said: “We were catching the usual variety of coarse fish species during our survey when I was amazed to see a sea lamprey rising to the surface. We’ve never caught these fantastic fish in the River Don before. Their sucker-like mouths and sharp teeth make them look very unusual and quite prehistoric. A few minutes later we caught another. There is a chance that they were trying to spawn so we released them back into the water straight away.”

In modern times, sea lamprey numbers have declined across Europe. Weirs and dams have prevented adult fish from swimming upstream to their spawning grounds. The Environment Agency and its partners, including the Don Catchment Rivers Trust, are now working on a ‘fish highway’ for the river, where fish passes and weir removals provide free access for all species of fish between the sea and the upper river.