SEATTLE (AP) – Ships moving through a busy channel off Washington’s San Juan Island are slowing down this summer to study whether that can reduce noise to protect endangered Puget Sound orcas.

The orcas spend summer months in Haro Strait, a major shipping channel in the Salish Sea that is also critical habitat for the whales.

The trial, led by the Vancouver Fraser Port Authority, hopes to understand whether reducing commercial vessel speeds can reduce underwater noise. Orcas use clicks, calls and other sounds to forage mainly for salmon, navigate and communicate.

Noise and other impacts from vessels is one of three major threats facing the whales that currently number only 78. Lack of prey and pollution are the others.

The trial asks cruise ships, ferries, bulk containers and other commercial vessels to voluntarily slow to 11 knots through Haro Strait. The project ends Oct. 6.