Ship noise may be making it harder for endangered orcas (Orcinus orca) that live in the coastal waters off Seattle, Washington, to catch salmon. Known to scientists as Southern Resident Killer Whales, this population comprises the only known resident orcas in the United States. In the late 1800s, they numbered about 200. But their numbers crashed in the 1960s, after some 47 were captured for display. Today, there are about 80, and they are protected by the Endangered Species Act. The whales already suffer from depleted stocks of Chinook salmon. Now, scientists report online today in PeerJ that commercial ships entering Haro Strait where the orcas live (as shown in the photo above), are likely interfering with the calls the whales make to communicate and locate prey. For 28 months, from March 2011 to October 2013, the researchers used a hydrophone placed 50 meters offshore in the center of the orcas’ summertime habitat to measure the noise from 1582 individual ships, including ore carriers, tugs, oil tankers, cargo, military, yachts, and fishing vessels. They found that ships are radiating underwater noise at high frequencies, 10,000 to 40,000 hertz—the same range that orcas and other toothed whales use. Although the scientists do not yet know specifically how the ships’ sounds are affecting the orcas, they note that other researchers have shown that the whales increase the amplitude of their most common calls when loud boats pass nearby. The study adds to global concerns about commercial ships’ noise and whales’ (including baleen whales, like blue whales) hearing. For instance, scientists have found that North Atlantic right whales have lower stress levels in areas without the sound of ships. Quieting technology to limit ships’ noise already exists, and is used by the military vessels, which are surprisingly silent, the scientists say. And, they note, there’s potentially an even easier fix: Slow down.