September 11, 2024, 10:54 am | Read time: 4 minutes
Whale experts, marine biologists, and animal rights activists have been sounding the alarm for some time. Man-made ocean noise is said to have devastating consequences for marine life. A study has now shown that ship noise in the oceans causes enormous disruption to orca hunting. PETBOOK explains the implications of this.
If you picture the world’s oceans as serene havens of tranquility, where the only sounds are the waves and the occasional song of whales, you’re sorely mistaken. Underwater noise has now reached deafening levels. This fact is confirmed by marine biologist Fabian Ritter of the Whale and Dolphin Conservation (WDC). In an interview with PETBOOK, the expert explains: “Many whales live along very busy shipping lanes, such as the Strait of Gibraltar. There is underwater noise, like living right next to a highway.”
Underwater noise puts whales under stress
This results in stress for whales and dolphins. This triggers reactions akin to those in humans, such as elevated stress hormones and a heightened vulnerability to diseases. A study by researchers from the University of Washington and the National Oceanic and Atmospheric Administration has now taken a closer look at the effects of underwater noise on marine life. It concluded that ship noise disturbs orca whales enormously when hunting.
The researchers focused their attention on the Salish Sea – the inland coastal waters of Washington and British Columbia. Here, two distinct populations of fish-eating killer whales reside. These are the northern and southern resident orcas. Yet, even in their aquatic realm, these marine mammals are not safe from human impact.
Orcas are threatened with extinction
Orcas are grappling with ocean pollution, the initial signs of climate change, and the depletion of salmon stocks, their primary food source. Although the population of northern orcas in the Salish Sea has grown to more than 300 animals, the population of southern orcas is stagnating at around 75 individuals. These whales are, therefore, still threatened with extinction.
In a paper published on September 10 in the journal “Global Change Biology,” the research team reports on underwater noise pollution – from both large and small ships. According to the researchers, this noise compels the orcas to spend more time and energy hunting fish. Accordingly, the noise reduces the overall success of their hunting efforts. The group of southern orcas is probably particularly affected, as they are more likely to be in parts of the Salish Sea where there is a lot of ship traffic1
“Ship noise has a negative impact on every step of hunting behavior
Lead author Jennifer Tennessen from the UW Center for Ecosystem Sentinels elucidates: “Ship noise detrimentally impacts every phase of the northern and southern orcas’ hunting behavior, from foraging and stalking to the actual capture of prey.” This could possibly be the reason why the population of southern orcas has not recovered.
“One factor hindering their recovery is the availability and accessibility of their preferred prey: salmon. “The presence of noise further complicates the challenge of locating and capturing prey that is already elusive,” the study asserts.
It’s important to note that orcas rely on echolocation to search for food. These marine mammals emit short clicking sounds through the water, which bounce off other objects. These signals then return to the orcas as echoes, containing information about the type of prey, its size, and location. This enables orcas to initiate a complex tracking and capture procedure when they spot salmon. The hunters rely on increased echolocation and deep dives to try and catch the fish.
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Noise affects females more than males
As you can imagine, constant noise makes it more difficult for whales to echolocate and is not particularly attractive to prey. To prove this thesis, the researchers analyzed the movements of the northern and southern orcas. They did this using digital tags roughly the size of a cell phone. These were attached with suction cups under the dorsal fin of the orcas. Thus, they could record important data such as body movements, position, depth, and sound level at the whales’ location.
Specifically, the researchers analyzed data from 25 Dtags that were attached to orcas for several hours on several days between 2009 and 2014. The scientists were able to see that ship noise – especially from propellers – increases the noise level in the water. The noise impaired the whales’ ability to transmit, hear, and interpret information about their prey.
The research team also observed that females were disproportionately affected by the noise. They were less likely to pursue prey that they had discovered during the noise. The exact reason for this could not be determined from the D-tag recordings.