Ship noise extends to high sound frequencies, which endangered killer whales use to communicate and find prey. Such finding hinders the species from hearing each other and may cause harm.
Endangered orcas in the Pacific Ocean catch salmon for food. However, the noise of passing ships may interfere with the species' ability to cooperate with its kind and be the dangerous predators that they are.
Underwater Noise Pollution
Underwater noise pollution is one of the most rampant threats that marine animals face. According to records, the rate of low frequency ship noise has grown by 10-fold from the 1960s. Such growth can be attributed to the increasing number of commercial ships sailing the oceans.
Baleen whales use low frequency noise. There have been increasing evidence that it may impair the species' ability to communicate and subsequently survive in the waters.
The big question now is could ship noise extend to higher frequencies and affect animals such as endangered killer whales that use it?
Extending From Low To High Frequency
American researchers measured ship noise of about 1,600 different ships that passed through Haro Strait, in Washington State for about 3,000 times.
The goal of the study is to determine the effects of ship noise, understand its nature and see if it can shift from low to high frequencies.
The scientists measured a wide range of mid to high frequencies from 11 Hz to 40,000 Hz to cover what
the orcas use to communicate.
The findings show that ships are accountable for low, mid and high frequency background noise levels, including 20,000 Hz, which is the optimal level suited for the hearing abilities of killer whales.
The results imply that killer whales that settle near shipping lanes are in danger of impaired communication and echolocation.
The Most Dangerous Ships
The study also looked at the most dangerous ships for the orcas. The researchers found that container vessels have the highest source levels at all frequencies below 10,000 Hz.
Military ships are responsible for some at the lowest levels.
This information suggests that applying silencing technologies to commercial ships may be a good noise mitigation method.
What Can Be Done?
"We recommend that future ship noise studies statistically characterize populations of ships - both their broadband and spectrum source levels," the researchers wrote.
They also suggest slowing down because they found that reducing the speed of ships by one knot decreases the broadband noise by 1 dB.
The study was published in the journal PeerJ on Tuesday.