A juvenile Short-snouted Seahorse, Hippocampus hippocampus has been found in the River Thames at Greenwich, London raising hopes that the species may well be breeding in the area.
Its discovery continues the remarkable recovery of the Thames river and estuary system which has been devastated by centuries of pollution.
The discovery of possible breeding colonies further down the river in Dagenham were kept secret until 2008 so that legislation could be put in place to protect them, but this new capture is the furthest upstream they have ever been found.
Due to a combination of the size of the fish and their poor swimming ability it is hoped that it may be from an as yet undiscovered colony living around the centre of the city.
Environment Agency fisheries officer Emma Barton said: "This is a really good sign that seahorse populations are not only increasing, but spreading to locations where they haven't been seen before. We routinely survey the Thames at this time of year and this is a really exciting discovery".
The 5cm/2" long seahorse was released unharmed back into the river after its capture.
Hippocampus hippocampus grow to around 15cm/6" and are more commonly found in the Eastern Atlantic and Mediterranean, but are known to be distributed along the south coast of England and Ireland, typically in the shallow muddy waters of estuaries or inshore amongst sea grass or seaweed beds.
They are one of only two species of seahorse found in UK waters, the other being the Long-snouted seahorse, Hippocampus guttulatus which is easily distinguished from the fish found in London not only by its longer nose, but by fleshy protuberances along its head and back which give the fish a 'mane' like their equine namesakes.
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