The growth of commercial fishing is potentially interfering with orcas abilities to catch their dinner, scientists say.
The endangered killer whales send out a click and listen to the echoes to determine where there next meal is.
Increased commercial shipping has raised the intensity of low-frequency noise almost 10-fold since the 1960s. There is growing evidence these noises impact baleen whales' ability to communicate, as they too use low-frequency noise.
In a new study, scientists wanted to find out whether ships emit mid- and high-frequency noise, which orcas and other toothed whales use, and which potentially interferes with their ability to communicate and catch their dinner.
Male orca 'Ruffles' uses echolocation to find his food as a tanker approaches him in Haro Strait (Supplied)
Scientists measured the noise of approximately 1600 unique ships at a range of frequencies from 10 Hz to 40,000 Hz as they passed through Haro Strait in Washington State.
This area is the core critical habitat for the endangered Southern Resident killer whales -- salmon-eating orcas which are iconic in the Pacific Northwest and which support a multimillion dollar ecotourism industry in the U.S. and Canada.
The results show that ships are responsible for elevated background noise levels not only at low frequencies but also at medium and higher frequencies. This included at 20,000 Hz where killer whales hear best.
This means that in coastal environments where marine mammals live within a few kilometres of shipping lanes, ship noise has the potential to interfere with both communication and echolocation -- the biological sonar used by several kinds of animals.
The scientists found container ships had the highest median source levels (at all frequencies below 20,000 Hz). Military vessels had some of the lowest levels, which means using quieting technology the military ships use for the commercial sector could be a successful noise mitigation strategy.
Another potential way to reduce noise pollution is to simply slow down, the study found. On average, each reduction in a ship's speed by 1 knot could reduce broadband noise levels by 1 dB.