Humpback whales' swimming speed, feeding and resting behaviors disrupted by loud tourist boats: Study
Whale watching offers enthusiasts a glimpse into the secret lives of ocean giants but that comes at a cost. According to a new study, humpback whales find the noise emitted from the tourist boats intrusive. It sends them into a frenzy, ultimately affecting their feeding and resting behavior.
The researchers from Aarhus University arrived at these findings after studying how mothers and calves respond to various noise levels. These findings raise questions on what it could mean in the long-term for the population: "Are the calves smaller and are they more likely to die? Are they more likely to not make it through the first journey to the feeding ground?" Dr. David Lusseau, Professor of Behavioural Biology at the University of Aberdeen, told MEA WorldWide (MEAWW).
To minimize the intrusion on humpback whales, Dr. Kate R. Sprogis, the lead author of the study, is now calling for noise-emission regulations for tourist boats. They recommend that it stays below 150 decibels. "If you want to have tourism and you want it to be sustainable, and you want one thing for sure: your boats have to be less loud. And the less loud they are, the better," Dr. Lusseau, who was not involved in the study, said.
Lusseau compares the noise to living next to a loud highway or a busy street. For long, scientists have known that humans activities such as shipping, gas exploration, and even offshore farms have been creating noise pollution in the oceans. But tourist boats have received little attention.
Whale watching took off as a recreational activity in the 1990s as an alternative to commercial whaling, which was banned in 1985. Soon, whale watching grew into a multi-million dollar business. In the meantime, experts have observed that when tourist boats are around, the humpback whales behave abnormally: they dive, change course, swim faster, breathe more often, disperse, and make unusual sounds.
The new study offers insights into the impacts of tourist boats on the humpback population in the Exmouth Gulf on the west coast of Australia. Dr. Sprogis used underwater speakers that mimic three volumes of sounds coming from boat engines. They used a drone equipped with a video camera to understand the whales' behavior to follow the 100-meter distance rule.
Mothers and calves seemed undisturbed at lower volumes. However, that changed when the noise grew. At the highest of 172 decibels (a loud boat), the resting time of the mothers dropped by 30% and their breathing rate doubled, their swimming speed also rose by 37%, according to the study.
Mothers spend less time resting while dealing with the noise. As a result, they may not have the energy to feed their offspring, fend off predators and unwanted males, and to migrate, Sprogis explained.
"For the calves, multiple disturbances can also mean that they don't get enough milk: In a short time, they have to grow big and strong enough to be able to cope with the migration to colder regions and to minimize the risk of being predated upon by sharks and killer whales," she added.
Noise affects other species of whales and dolphins too. The amount of noise it makes is problematic and is applicable across all species that use sound as their main mean after understanding, Dr. Lusseau said.
Commenting on the study, Dr. Lusseau said: "We are calling for emission standards in the same way that we have emission standards over pollutants. Thinking of noise as a pollutant in the oceans is right and proper. It's an appropriate call."
The study is published in eLife.