Ship noises severely impact killer whale populations, disorienting the endangered marine mammals and making it difficult for them to track prey, researchers have recently determined.
The findings were featured in the journal PeerJ on Tuesday, February 2, and were based on an analysis carried out by Scott Veirs, oceanographer and environmental scientist at the Marine Science and Sustainability School.
The purpose was to determine if ship noise negatively influences killer whales also, or if its effects are only limited to humpback whales, blue whales, grey whales and other types of baleen whales (Mysticeti).
Prior studies had shown that, when exposed to noise pollution, baleen whales tend to be experience difficulties when communicating through vocalizations or when navigating through their surroundings.
That’s because the audio frequency to which they are especially responsive tends to be low, just like the one characterizing the sounds that ships make as they move through the ocean.
For example, Curvier’s beaked whales are 50% less likely to effectively hunt for quarry, because their echolocation abilities are greatly reduced by disturbing sounds made by vessels.
Now, it appears that even toothed whales and oceanic dolphins are also under considerable strain after being exposed to ship noises.
By reviewing the sounds made by approximately 1,600 as they crossed the Haro Strait, near Washington state, approximately 3,000 times, study authors discovered that the vessels produce not just low-frequency sounds, but also medium and high frequency ones, reaching around 20,000 Hz.
These are exactly the sounds to which killer whales respond the most, and which they are the most likely to hear and be distracted by.
As a result, the orcas can no longer swim through the ocean as confidently as before, finding it more and more difficult to identify prey or to keep away from the shore.
Such perturbations to the marine mammals’ echolocation abilities are particularly alarming for Washington’s coastline, given the fact that this region is where the severely depleted Southern Resident Killer Whale population tends to be concentrated.
On the other hand, the same risks are encountered by all the killer whales that prefer coastal locations, where the racket caused by passing vessels is especially deafening and strident, boosted by the low water levels.
Study authors believe that a solution may be at hand however, since apparently not all ship noises have the same impact, with some being much more damaging than others.
More precisely, naval ships tend to be much stealthier, producing much less commotion and clamor than the one caused by their commercial counterparts.
This shows that it would be possible to reduce the amplitude of sounds made by container vessels by adopting military technology, in order to limit the disturbances caused to toothed whales and dolphins.
For instance, by lowering speed by around a knot (one nautical mile per hour), ship noises would be diminished by approximately 1 decibel. Therefore, by curbing velocity by about 6 knots, sound waves would become around half as forceful as before.
Like researchers point out, such changes meant to limit the impact of underwater noise pollution would be essential in preserving the killer whale population, especially now when this marine species is already under considerable strain, due to other factors.
For example, whaling remains a common practice in Japan and other parts regions around the world, and food sources that these aquatic creatures relied on (Chinook salmon, squid, sea turtles, seals etc.) are getting sparser and sparser.
Moreover, climate change has caused the emergence of more and more algal blooms, which often reach killer whales through the food chain, poisoning them with dangerous neurotoxins.
Another source of contamination is represented by polychlorinated biphenyls (PCBs), which may have been prohibited in 1986, but can still be found at extremely high concentrations in the adipose tissue of many bottlenose dolphins and orcas.
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