The killer whale population has declined 20 percent since 1995, and scientists think they’ve found one of the reasons why: whale watchers. The motorized boats that serve whale-watchers disrupt the orcas’ sonar, reducing its efficiency by as much as 99 percent. That means whales have to swim harder and longer to find food; in so doing, their bodies consume more blubber, which is a storehouse of toxic chemicals. Seattle-area researchers found that adult whales burn nearly 20 percent more energy than they did before whale watching became popular; these days, close to 100 boats follow orca pods every day. Large boats are expected to keep a safe distance from the giant whales, but smaller ones frequently creep up to within a few yards. Ironically, whale-watching has helped raise public awareness about and funding for the overall plight of killer whales.