The series took almost five years to make, involving nearly 200 filming locations. The fact that most of the
ocean environment remains a mystery presented the production team with many challenges. Besides witnessing some animal behaviours for the first time, the crew also observed some that were new to science. The producers were helped by marine scientists all over the world with state-of-the-art equipment.
Blue whales – whose migration routes were previously unknown – were located by air, after some of the animals had been given temporary radio tags. The camera team spent three years on standby, using a
microlight to land on the water nearby when they finally caught up with the creatures in the
Gulf of California. The open ocean proved more difficult and over 400 days were spent in often unsuccessful filming trips. After six weeks, the crew chanced upon a
school of
spinner dolphins, which in turn led them to a shoal of
tuna. Off
Mexico, the behaviour of a flock of
frigatebirds guided the cameramen to a group of
sailfish and
marlin: the fastest inhabitants of the sea. Near the coast of
Natal in
South Africa, the team spent two seasons attempting to film the annual
sardine run, a huge congregation of predators such as
sharks and
dolphins, that assembles to feast on the
migrating fish by corralling them into "bait balls". Meanwhile, in
Monterey Bay,
orca were documented attacking
gray whales and killing a calf. Filming in the deep ocean required the use of special
submersibles. One of them enabled the crew to dive over a mile into the San Diego trench, where the carcass of a 40-ton gray whale had been placed to attract a large variety of scavengers. When first transmitted on
BBC One, over 12 million people watched the series and it regularly achieved an audience share of over 30%. In 2018 a newly-discovered species of
phytoplankton (
Syracosphaera azureaplaneta) was named by scientists in honour of the programme, and in recognition of David Attenborough's contribution to promoting wider understanding and awareness of the oceanic environment. == Episodes ==