One of the largest seahorses found to date was discovered off the Dorset coast.

Although 22cm seahorses are often found in Studland Bay, the latest discovery measured 23cm from head to toe.

This makes it the fourth largest seahorse to have been recorded in the British Isles.

The spiny seahorse was discovered by a local crab-fisher, Robin Guy, and was an accidental finding.

The seahorse was swiftly returned to the water after the Seahorse Trust asked for Robin to measure the animal against his hand.

The only larger seahorses discovered by local fishermen were found at Old Harry Rocks.

The largest of these was 34cms tall, making it the largest seahorse discovered anywhere in the world.

The trust has asked that anybody who discovers seahorses in the harbour should take a photograph against something measurable and send it to the trust.

Neil Garrick-Maidment, founder and director of the Seahorse Trust, has been studying marine animals for over five decades but found this one “particularly beautiful”.

He said: “Every sighting gives us a little bit more knowledge and experience for us to help the species further.”

Sightings of seahorses have been reported in the British Isles since 1721 and have no connection to ocean warming. Though sightings of seahorses often happen, the size of this animal made this case particularly unusual.

“More sightings are coming in,” Neil added.

“It is great that people are becoming conscious of how to respond, and really mind-blowing to know these seahorses are here in this harbour.”

Intentionally disturbing seahorses in their habitat without a licence is illegal, since they are a protected species, whereas the discoveries made by Robin and other amateur fishermen were accidental sightings.

Neil applied to make seahorses a protected species in 2002, but the fish only received this classification in 2010.

Though dead seahorses discovered on the harbour over the winter have still been useful to research carried out by the trust, Neil said it was “preferable when they are found alive and well”.

To the knowledge of the trust, the seahorse is still safely at sea after being quickly and carefully returned to the water.