Sea Monsters - broadcast on North America as Chased by Sea Monsters - was a documentary trilogy that first aired on BBC One on 9 September 2003. This is the second Walking with... programme to star Nigel Marven and was the last Walking with... special to air. It is also the only programme to be narrated by Karen Hayley.
The show is about Nigel Marven travelling back in time to visit the seven deadliest prehistoric seas. On his journey, he encounters many marine animals, from the predators to the prey. He travels to those time periods on a boat called The Ancient Mariner, a 24 metre long boat with a crew. His means of time travel is never shown but the closest thing to it is his time map, that show the seven deadliest seas and the creatures that live in them. On his dives, he wears a scuba set with a fullface mask so that he can narrate while under water. On some of the most dangerous dives, he uses a strong shark cage, which is spherical so that it is difficult for predators to bite it.
Unlike the other programmes, Sea Monsters has never had a UK DVD release. The programme was however featured on the US release of Chased by Dinosaurs and on a Region 2 Dutch DVD.
Wildlife adventurer Nigel Marven goes back in time to visit the seven most deadly seas until he reaches Hell's Aquarium, the most deadly sea of all time. Each time period he visits is more dangerous than the last.
He starts his voyage in the Ordovician and then later travels to the Triassic, the Devonian, the Eocene, the Pliocene, the Jurassic and finally the Cretaceous (or as he calls it: Hell's Aquarium, since it is the deadliest sea).
|Image||Episode title||Episode number||Original airdate|
|150px||Dangerous Seas||1||9 September, 2003|
|This episode marks the beginning of Nigel's quest as he travels back to the Ordovician to find the giant orthocone. He then ventures to the Triassic to encounter Cymbospondylus but on his journey there, he encounters nothosaurs and the creature that defies physics. His last trek of the episode is to the Devonian where he encounters the Dunkleosteus.|
|150px||Into the Jaws of Death||2||16 September, 2003|
|This episode starts with Nigel still in the Devonian escaping the wrath of Dunkleosteus. The episode then moves on to the Eocene where Nigel encounters a rhino-like elephant and the giant Basilosaurus. The episode then continues to the Pliocene where he encounters the bizarre Odobenocetops and the titanic shark Megalodon.|
|150px||To Hell and Back?||3||23 September, 2003|
|This episode starts with Nigel still in the Pliocene still trying to attach a camera to a Megalodon. The episode then moves on to the Jurassic where Nigel comes face-to-face with the giant fish Leedsichthys, the marine croc Metriorhynchus and the giant monster Liopleurodon. The episode concludes in the Cretaceous, Hell's Aquarium. There, Nigel encounters a plethora of sea monsters and then come face-to-face with the deadliest sea monster of all.|
- Full article: Sea Monsters companion book
A companion book to the trilogy was published by BBC Books on 16 October 2003. Instead of organising the chapters into the order of the most deadly seas, the book is presented in temporal order.