Blue Planet - Open Ocean
Focuses on life in the "marine deserts": seas that are furthest from land. Such waters contain the swiftest and most powerful of ocean hunters. A feeding frenzy is shown, as striped marlin, tuna and a Sei whale pick off a shoal of sardines until all within it have been consumed. Manta rays also gather to eat the eggs of spawning surgeonfish. Accumulations of plankton correspond to ocean 'boundaries' and consequently, schools of fish seek them out. This in turn attracts predators, and a sailfish is filmed on the attack. The only escape for smaller fish is to put as much distance between them and their pursuers as possible. Bluefin tuna are able to heat their bodies and so can hunt in colder conditions than the others of their species. Off the coast of New Zealand, an undersea volcano has formed an island and the nearby currents sweep many kinds of creatures to it, again creating huge feeding grounds. Another Pacific seamount is surrounded by hammerhead sharks, but not to seek food: they are there to allow other fish to clean them of parasites. However, others that are on the lookout for prey arrive in vast numbers. A large pod of common dolphins is too big to feed all at once and so splits up into smaller expeditions. One of these ends up near the Azores with a shoal of mackerel in its sights, but they have to compete for their quarry with an attendant flock of shearwaters and a group of adult yellowfin tuna.
