River Lamprey (Lampetra fluviatilis) and Sea Lamprey (Petromyzon marinus)
The river and sea lamprey are a primitive type of fish having a distinctive
suckered mouth but no jaws. Although numbers of lamprey have declined over
the last 100 years, the UK is still one of their strongholds. Sea and river
lampreys spend their adult life in the sea or estuaries but spawn and spend
the juvenile phase
in rivers. They use the Severn Estuary as a migratory passage to and from
their spawning and
nursery grounds in the rivers.