The final episode features the summer plankton bloom along the coast of British Columbia and Alaska. In winter, the coastal fjords and inlets are relatively lifeless, and the resident Steller sea lions must dive deeper and further from the coast to catch the widely-dispersed herring. Humpback whales overwinter in the warm Pacific waters off Hawaii, where new mothers suckle their calves. They begin their 3,000 mile journey north in early spring, when the sea lions also give birth to their young. Spring storms are a hazard for the sea lion colonies and some pups are inevitably lost, but these same storms disturb nutrients in the water which, together with the strengthening power of the sun, act as the catalysts for the plankton bloom. Huge shoals of herring arrive to spawn, turning the shallows milky white. The herring sift plankton from the water. In their wake come larger predators, including Pacific white-sided dolphins and killer whales. The latter are filmed attacking a male sea lion. Common murres dive under the herring shoals and pick off the fish from below, pinning them to the surface. Their defence is to form a bait ball, but gulls gathering on the surface attack them from above. The finale to the programme features unique underwater footage of humpbacks engulfing whole bait balls, and reveals their co-operative hunting behaviour called bubble-netting. The diary segment, "Swallowed by a Whale", looks at the challenges of filming the humpbacks and sea lions underwater.
Nature's Great Events is a wildlife documentary series made for BBC television, first shown in the UK on BBC One and BBC HD in February 2009. The series looks at how seasonal changes powered by the sun cause shifting weather patterns and ocean currents, which in turn create the conditions for some of the planet’s most spectacular wildlife events. Each episode focuses on the challenges and opportunities these changes present to a few key species. Nature's Great Events was produced by the BBC Natural History Unit in association with the Discovery Channel and Wanda Films. The British version of the series was narrated by David Attenborough. In the USA, the series was shown under the alternative title Nature's Most Amazing Events beginning on 29 May 2009 and was narrated by Hasani Issa. The title Nature's Great Events was previously used by Reader's Digest for a unrelated VHS series released in 1996. Source