Southern Resident killer whales suffered a significant population decline in the late 1990s and are now listed as endangered under the U.S. Endangered Species Act. Killer whales are exposed to disturbances from commercial and private vessels during the summer whale watch season, and whether such vessels change killer whale behavior is still unknown. In July 2006, the crew aboard the National Marine Fisheries Service vessel Noctiluca observed a "spy hopping" Southern Resident killer whale off San Juan Island, Washington. The Northwest Fisheries Science Center's marine mammal program also conducts innovative research to better understand killer whale ecology, taxonomy, physiology, and behavior.