Seahorses in the Thames

Eighteen months after the discovery by Zoological Society of London it has been announced that a colony of seahorses has been discovered in the Thames estuary. The discovery has been hailed as clear indicator of the increasing purity of the river’s water.

Alison Shaw, the Zoological Society of London’s marine and freshwater conservation manager, said: “These amazing creatures have been found in the Thames over the past 18 months during our wildlife monitoring work. It demonstrates that the Thames is becoming a sustainable habitat for a diversity of aquatic life.”

The short-snouted seahorses (see above for a picture of one bred in captivity in an Angelsey aquarium) in the Thames are commonly found around Africa and the Mediterranean but also sometimes near the southern coasts of Britain. Their usual habitat is shallow coastal waters rich in weeds and plant life, although they can be found as deep as 100ft. “They’re rarely found in Great Britain at all,” said Richard Harrington from the Marine Conservation Society. “If they are, then it is usually in the Channel Islands or near Dorset.”

Last year, however, juvenile seahorses of both the short-snouted and long-snouted species were found in the marina at Brighton, East Sussex. This was the first evidence to suggest the fish were actually breeding in British waters.

The Thames discovery illustrates the partial success of attempts to reduce pollution in a river once considered one of the dirtiest in Europe (Fifty years ago the river was declared biologically dead).

The clean-up has already resulted in the return of salmon, which were extinct in the Thames from 1833 until 1974 but are now breeding in Berkshire. Their regeneration has been aided by releases of juvenile fish. In 2006 a dead otter was found not far from Tower Bridge. Other sightings have confirmed that the mammal species could be staging a comeback.

Conservationists hope wildlife numbers will continue increasing but the Thames still suffers from periodic surges of pollution, especially after rainstorms, which tend to flush sewage from drains into the river. By 2019 the government plans to have built a 20-mile, £2 billion tunnel to collect such sewage and transport it to a treatment plant in east London.

The lower reaches of the river are often visited by porpoises and dolphins; in 2006 a northern bottlenose whale was watched by crowds of people as it swam upriver as far as Chelsea. It died while being rescued.

Some experts suspect that the decrease in pollutants is only one of the factors behind the appearance of se horses in the Thames. “There has also been a small but definite rise in the temperature of the North Sea and English Channel,” Harrington said, “and this may well be the cause of all the new and exciting species we are seeing.”