The sea lamprey (Petromyzon marinus) is the largest of the three lamprey species in the UK. Lamprey fossils have been found in the late Silurian and Devonian periods, approximately 450 million years ago.
Sea lamprey are a migratory fish laying their eggs in clean, sandy gravels in rivers. The young larvae then move to the soft marginal silt of the river to grow, feeding on the algae, bacteria and detritus in the mud. When they are ready they will migrate to sea and start to feed parasitically on other fish by attaching themselves with their sucker-like mouths. They then migrate back into freshwater to spawn, after which they die. During this migration they don’t feed and focus their energy on getting to suitable spawning grounds.
Appearance: adults are eel-like in size and shape, but they have no gill plates, paired fins or a jawed mouth. They have a mottled brownish grey colouration, which becomes an orange mottling when spawning. The mouth is a disc with numerous teeth, which it uses to attach and then rasp onto its host fish.
Typical size: 50-100cm
Lifespan: 5 to 8 years
When to see them: Juvenile sea lamprey spend their time in the mud, so you won’t see them, and the adults are out at sea. However, the adults migrate back into rivers in May/June when they can be seen. After they have bred they die and people often report seeing their carcasses.
Last date edited: 24 December 2020