An alarming new study has found that killer whales are being harmed by shipping traffic far more than scientists had thought before.

A new study on shipping traffic in the Salish Sea, the body of water between Seattle and Vancouver, has found that the noise caused by ships often dips into the same frequencies that orcas use to hunt and communicate, according to a Vancouver Sun report.

Killer whales need to communicate with other killer whales through a series of clicks, and shipping noise can disrupt that process, preventing them from honing in on a meal.

This was a surprising find for scientists because they had assumed shipping traffic used a frequency below that of killer whales, but that was because scientists had been listening too far away, and the propellers on many ships are turning faster than they were designed to. As a result, the noise can interfere with the killer whales’ communications.

Scott Veirs, the lead author of the report who works at Seattle’s Beam Reach Marine Science and Sustainability School, said that researchers came to their conclusions by installing listening devices in habitats rich with orcas and calibrated those devices to a wide range of frequencies, including those used by killer whales, according to the report. He said that it is obvious from the data collected that the frequency the killer whales use is filled with shipping noise.

“Because these orcas, like other toothed whales, use mid-and high-frequencies to communicate and find their prey, the study measured a wide range of frequencies (10 Hz to 40,000 Hz),” according to a statement with regards to the study. “The results show that ships are responsible for elevated background noise levels not only at low frequencies as expected, but also at medium and higher frequencies (including at 20,000 Hz where killer whales hear best). This means that in coastal environments where marine mammals live within a few kilometers of shipping lanes, ship noise has the potential to interfere with both communication and echolocation.”