"Call of the Killer Whale," a two-hour documentary airing on PBS, begins by focusing on the story of the world's most famous killer whale, Keiko, the star of the film "Free Willy," who was famously set free after being rescued from a Mexican circus. Keiko's story is useful to illustrate the challenges of reintroducing an orca into the wild, having to teach it how to feed off live fish (as opposed to dead ones tossed regularly into its mouth) and how to develop other survival skills basic to wild orcas. The message we take away from the first part of the film is that captive whales rarely live very long and have a tough time of it if they're reintroduced into the wild. Keiko made it to 27, before succumbing in a Norwegian fjord. The second and more powerful part of the film looks at the drastically shrinking orca population around the world and attributes the decrease, inevitably, to pollution and human enterprise that upsets nature's delicate balance. Although PCBs were banned in the '70s, the chemicals, as well as other contaminants in the air and water, can remain in an orca's system for decades, which has resulted in calves born with birth defects. The more challenging issue, and the one that even more tellingly shows the fragility of nature's interconnectedness, has to do with the fate of the salmon population. In the Pacific Northwest, for example, salmon have been the orca's main source of food. We all know that the salmon population is decreasing, but as Cousteau and other scientists contend, part of the reason the fish are decreasing is that man has created salmon farms which have actually hurt wild salmon because the cultivated fish hog all the food in shared waters.