“Ocean Giants,” the documentary for PBS's “Nature” series (released in a Blu-ray/DVD package) follows the majestic creatures from the Indian Ocean to the Arctic. A pair of underwater photographers accompanies various scientific expeditions, capturing life among the whales as human eyes have never before seen it. Snapping the beasts under the surface isn't easy. Some whales live for centuries and have long memories; one bowhead was discovered with a circa 1890 harpoon head still embedded in its flesh. The series' selling point for some viewers might be the jousting of male humpbacks over femalesa bit like a bar fight with multi-ton belligerentsbravely photographed against the threat of huge swishing tails and maelstroms of swirling foam. Mostly, however, “Ocean Giants” shows the mysterious behemoths as they feed, swim and sing to each other, cutting beautifully graceful figures in the depths.
