Return of the lamprey – ancient, ugly and swimming up British rivers

Paul Brown

Sunday 15 May 201621.30 BSTLast modified on Monday 16 May 201600.00 BST

The sea lamprey, Petromyzon marinus, is most likely to be seen in British rivers at this time of year as the adults swim upstream to spawn.

They are remarkable creatures but good looks are not one of their attributes. They resemble an eel and have a permanently open mouth with a great number of teeth. They also have some nasty parasitic habits.

Perhaps the most extraordinary thing about them is that they have been around since well before the dinosaurs, and with 360-million-year-old fossils looking remarkably like modern lampreys, they are said to be the oldest vertebrates.

Having thrived all that time they have suffered greatly in the UK from pollution and human interference with the flow of rivers, which has prevented them reaching their spawning grounds.

However, the cleaning up of the rivers and provision of passes to allow them to get round weirs and other obstructions has allowed them to recolonize rivers that had not seen a lamprey for many years, including the Great Ouse, Trent, Derwent and Wear.

Like salmon they stop eating when they leave the sea and travel to the upper reaches of the river where they lay eggs in troughs in gravel. Until the end of June this normally secretive creature, sometimes more than a metre long, can be seen swimming up river, looking more like a snake than a fish.

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