First seals, now a sea horse - but is this a sign of cleaner water in the Thames, or global warming?

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The discovery of a sea horse in the Thames estuary has been hailed as a sign that what was once the outlet for the dirtiest river in Britain is returning to ecological health.

The discovery of a sea horse in the Thames estuary has been hailed as a sign that what was once the outlet for the dirtiest river in Britain is returning to ecological health.

The short-snouted sea horse, Hippocampus hippocampus, last seen in the estuary nearly 30 years ago, was spotted among the seaweed by a fisherman, Brian Baker, as he hauled in his nets to return to Leigh-on-Sea, Essex.

Measuring no more than 15cm in length, it has now been placed on display at the Southend Sealife Adventure centre, where it is seen as proof of the Thames' new ability to support aquatic life. Some also see it as an indication that the waters are steadily warming.

There are other indications of that trend. Red mullet, once almost unheard of, is becoming increasingly common in the estuary. Anchovies, a stalwart of the Mediterranean, have also been caught, and the river is said to be "alive" with mackerel this summer.

The common European sea bass, once at the northern limit of its range, is so at home that the estuary has become a designated nursery for the breed. Fisherman are also seeing increasing numbers of little egrets off the Essex marshes, once considered an extremely rare visitor.

These new arrivals are finding an hospitable environment. Water quality has been greatly improved by the overhaul of two sewage outlets at Crossends and Beckton. Factories and power stations dotted along the Kent and Essex banks have also cleaned up their act.

David Knapp, of the sealife centre, believes the discovery of the sea horse is dramatic proof of the improving lot of the Thames. The last recorded find was in the gates of a power station in 1976. "The sea horse is extremely sensitive to dirty water and would simply not be here if there was significant pollution," Mr Knapp said.

Mr Baker, 56, has been fishing out of Leigh-on-Sea for 30 years. He works alone on board his trawler, the 22ft (7m) Nyella, specialising in harvesting the estuary's muddy floor for Dover sole. "The water is getting a lot cleaner, but its also getting a lot warmer, despite what the politicians might say," he said yesterday.

Sea horses are typically found in southern waters, such as the Bay of Biscay. They are unique in the animal kingdom in that the female passes the eggs to the male, where they are fertilised in a "marsupial-style" pouch. It is the male that gives birth to live young and couples normally stay faithful for life.

Although it is a fish, it has no scales. Its ringed appearance comes from bony plates and the pattern on the head of each is as individual as a human fingerprint.

While the sea horse has been around for more than 40 million years, it is coming under increasing pressure in its main habitat, coastal tropical and temperate waters. One of the biggest threats comes from its reputation for possessing magical and healing powers, which have made it a popular "cure" in traditional Chinese medicine. Their beauty and behaviour have also made them vulnerable to collectors, with millions living out their lives as aquarium curiosities.

"This is an exciting sighting," said Kelvin Boot, director of the National Marine Aquarium at Plymouth. "These are wonderful, charismatic fish. They are instantly recognisable, may have given rise to the dragon legend and even breathe 'smoke', a soupy exhalation of its food. We still don't really understand their distribution but here they would be on the northern limits of their range."

There are two species of sea horse in Britain, the other being the long-snouted ( Hippocampus guttulatus), normally seen around the Channel Islands and the South-west coast. The Great British Sea Horse Survey, established in 1996, reports increasing numbers.

Yet the cleaner waters that attracted this sea horse are presenting new challenges for fishermen. While a generation ago there were more than 50 boats operating from the Thames estuary ports, now there are fewer than a dozen.

The fishing quota for sole is 110 tonnes a year for the entire North Sea fleet below 10 metres, and Mr Baker says it is not unusual to see more than 20 seals bobbing around in the estuary channels. "Each eats four to
five tonnes of fish a year. It doesn't take many for the entire British quota to be going down their throats. I like to see them about, but there are more and more every year."

NEW ARRIVALS

Red mullet

Growing up to 30cm long, the red mullet is fished for around the Canary Islands, in the Mediterranean and in the Black Sea. The fish are commonly found on the gravel, sand and mud bottoms of the sea.

Common seal

The most common of the pinnipeds (fin-footed mammals), there are about 500,000 worldwide.
Growing to nearly 6ft in length, it tends to stay within 12 miles of shore.

Little egret

Formally listed as a rare breeding species, this small white heron migrated to Britain for the first time in 1989.
A distinctive bird with a long black bill, the little egret is now breeding on south coast sites, where it huntsfish in shallow waters.

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