We know that plastics littering the oceans are a major problem to the marine environment, but if you were to dip your head under the waves near a busy port, you’d be able to hear another considerable problem. The background hum and din of commercial ships passing up and down the coast could be harming the survival of whales and dolphins, which rely on the clicking and listening of biosonar to do everything from talk to each other to hunt. A recent paper published in PeerJ has looked into how the noise is affecting orcas off the Washington state coast.
While a growing body of evidence shows that ships produce low-frequency noises that can disrupt the communication, and thus survival, of baleen whales, little has been done to investigate whether or not ships also produce noise that affects toothed whales, which tend to use higher frequency calls. If so, then the massive increase in the passage of commercial ships, estimated to have gone up by a factor of 10 in the past 50 years, could be having a major impact on the ability of toothed whales to hunt, as well as talk to each other.
The whales off Washington state's coast may find it difficult to hunt with all the background noise from cargo ships. beamreach.org
To try and answer this question, U.S. researchers recorded the hum produced by ships as they passed up and down the Washington state coast. This coastal area is of particular importance, as it contains the core range of the endangered Southern Resident killer whales, which display distinct social, behavioral, and linguistic characteristics compared to other orcas. As of 2015, there were only 84 individual Southern Resident killer whales recorded, making the understanding of what negatively impacts these creatures vitally important.
By measuring the noise of nearly 1,600 ships as they passed through Haro Strait, Washington, they found that the ships were producing significant amounts of background noise. They discovered that this elevated din coming from the ships covered not only the lower frequencies as expected, but also the medium to higher frequencies of around 20,000 Hz, at which orcas hear the best. This, suspect the researchers, means that the extra traffic from the commercial ships is almost certainly interfering with their ability to communicate with each other, as well as hunt the fish they feed on.
Interestingly, while the researchers found that container ships were the biggest problem, military vessels had some of the lowest levels of noise pollution. If the commercial sector used the military's quieter technology on their own ships, the researchers suggest, it could be a way of limiting the damage that the underwater hum causes to the whales, and could lead to a more hushed marine environment.