The wonder of Pembrokeshire’s ocean wildlife will be showcased on BBC One this weekend in the final aired episode of Sir David Attenborough’s Wild Isles.

Filmed over the course of three years, the five-part series aims to shine a light on the challenges affecting the British Isles and celebrate nature that exists on our doorsteps.

Episode Five: Ocean will air on BBC One and iPlayer on Sunday 9th April at 7pm.

It features the mass migration of spider crabs under the waters of the Pembrokeshire coast and the incredible journey of Manx shearwater chicks as they set off on their first migratory journey to South America.

Western Telegraph: Sir David Attenborough filming with Manx shearwaters on Skomer for BBC 1's Wild Isles. Sir David Attenborough filming with Manx shearwaters on Skomer for BBC 1's Wild Isles. (Image: Wild Isles: Silverback Films / BBC)

‘’Here in Britain and Ireland we have some of the richest seas in Europe,” said Sir David.

“Our varied coastline, if you include all the many offshore islands, is over 22,000 miles long and none of us live more than 70 miles away from the sea. Yet few of us have seen the wonders beyond the beach and beneath the waves.

Western Telegraph: The mass migration of spider crabs off the coast of Pembrokeshire features in Sunday's episode of Wild Isles. The mass migration of spider crabs off the coast of Pembrokeshire features in Sunday's episode of Wild Isles. (Image: Wild Isles: Silverback Films/BBC)

“In this episode we will take you from the most southerly point of the United Kingdom to the furthest north to explain why our seas can be so productive and reveal the threats that they face today.’’

The spider crab footage, filmed on the shallow seabed off Pembrokeshire and off Dorset depicts a mass migration of epic scale. For just a few days every year, hordes of crabs march together as one.

On Skomer we see huge numbers of Manx shearwater that rely on our shores to mate and rear their young.

Western Telegraph: A Manx shearwater on Skomer Island in Sunday's episode of Wild Isles. A Manx shearwater on Skomer Island in Sunday's episode of Wild Isles. (Image: Wild Isles: Silverback Films/ BBC)

In a touching piece to camera, Sir David Attenborough bids a fledgling chick farewell as it starts its journey many thousands of miles across the oceans to South America.

A perfect example of how important the abundant seas of Britain and Ireland are to the survival of wildlife worldwide Sir David also signs off from Skomer Island at the end of the Ocean episode.

Producer Gisle Sverdrup said: “I hope that people watching this series will gain a new appreciation of how exciting and surprising the wildlife is on and around the British Isles.

Western Telegraph: A pair of Manx Shearwater on Skomer Island. The birds and their amazing migratory journey will feature in BBC 1's Wild Isles this Sunday. A pair of Manx Shearwater on Skomer Island. The birds and their amazing migratory journey will feature in BBC 1's Wild Isles this Sunday. (Image: Wild Isles: Silverback Films/ BBC)

“The Ocean episode showcases some of the amazingly colourful and charismatic animals living around our islands and I hope that it will change people’s perception of the diversity and importance of our seas.”

Wild Isles is a Silverback Films series for BBC One and iPlayer. Presented by Sir David Attenborough, coproduced by The Open University, the RSPB and WWF.