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From the BBC:
Rare seahorses breeding in Thames
Colonies of rare seahorses are living and breeding in the River Thames, conservationists have revealed.
The short-snouted variety are endangered and normally live around the Canary Islands and Italy.
Experts at London Zoo said the species had been found at Dagenham in east London and Tilbury and Southend in Essex, over the last 18 months.
The revelation coincided with new laws which came into force on Sunday to give the creatures protected status.
The seahorses, or Hippocampus hippocampus, are now protected under the Wildlife and Countryside Act 1981.
Short snouted seahorses in the Netherlands here.
Weedy sea dragons: here.
British seahorses: here.
Whales, dolphins and seals returning to the Thames: here.