It’s tough to be a human in the 21st century. Sure, we don’t have to worry about predators or scavenging for our next meal like our ancestors, but we’re inundated by so much buzz that it can be hard to think. Crowded places, social media, blaring news headlines, tabloids at the checkout line, terrible traffic patterns… noise, audible and not, is everywhere. You would think that as humans, we’d sympathize with others feeling the unwelcome burdens of too much stimulation. But as Dr. Robert Schick of the Nicholas School of the Environment and the Marine Geospatial Ecology Lab (MGEL) explained at a talk on November 1st, sometimes we forget about noise that isn’t on land. For years, whales — and specifically, beaked whales — have been feeling the impacts of sound stressors in the ocean.
Human activity generates a lot of buzzing in the ocean. For example, there’s the incredible amount of noise generated by renewable energy such as offshore wind turbines. Then there’s shipping traffic — consider just the United Kingdom, which reports that 90% of products sold in the country have to arrive by boat. But one of the projects at the MGEL focuses on a particular source of noise: military sonar, created by Lockheed Martin, which is the primary weapon that the U.S Navy utilizes to locate enemy submarines.
Navy sonar activity has been associated with mass strandings of beaked whales for a while. In the early 1990s, an unusual amount of whales were seen beached off the coast of the Canary Islands, the Ionian Sea in Greece, and in the Bahamas. But what’s the significance? Well, imagine that you’re at a really loud concert — the loudest rock bands in the world generally top out at 130 decibels. Then, imagine you’re a beaked whale, exposed to slow-rolling sound waves that can reach up to 235 decibels, which is way beyond the sound tolerance for humans and most animals. Sonar causes whales to migrate hundreds of miles away from their homes, bleed out of their eyes and ears, and beach themselves, leading to the mass strandings that scientists have observed.
This leads to the current MGEL project, co-lead by Duke Marine Lab director Dr. Andy Read and Dr. Brandon Southall in Cape Hatteras. Beaked whales dive to extremely low depths. “Imagine climbing the Burj Khalifa three times while holding your breath,” Schick said, to a room full of awestruck reactions. Needless to say, it’s hard to do that in silence — what happens when you factor in 235 decibels worth of sound disturbance?
The team uses satellite tags as well as DTAGs (digital acoustic tags) to tag whales and determine whether or not a whale was exposed to sonar. DTAGs have depth sensors, an accelerometer to see how an animal is moving, a hydrophone to hear what is happening, and a suction cup, ensuring that a whale isn’t physically implanted with a tag. However, this also leads to a limited duration of use. Satellite tags, on the other hand, feature no sound recording abilities, and have coarse dive data, but can be used for much longer. Utilizing these two tagging methods, Schick explained that the lab then embarks on a rather tedious process: “find a whale, hope it’s a beaked whale, wait forever, tag the whale, allow it to return to baseline, expose the whale to sound, then quantify what happens”.
There are lots of moving parts that can result in uncertainty. The team has to factor in and work around variables including simply the presence of whales, the weather, the gulf stream, spatial uncertainty, and the schedule of navy ships. However, through this research, the team has been able to map the locations of whales at given times, with given sound stressors, and further strengthen the link between sonar and strandings.
So what’s next? 2020 will see MGEL engaging in Spring and Fall field sessions, with one of the focuses being the addition of other sources of sound, such as wind and low-frequency data from ships. But research on strandings also raises ethical questions, furthering discussion about the issue.
The US Marine Mammal Protection Act of 1972 (MMPA) makes it “illegal—with certain exceptions—to ‘take’ a whale, dolphin, porpoise, seal, sea lion, manatee, dugong, sea otter, or polar bear in U.S. waters, or elsewhere by a U.S. citizen without a permit”. How does one categorize mass strandings — does sonar disturbance leading to forced migration constitute the “taking” of whales or simply an unfortunate result of the U.S. Navy’s need to track enemy subs? This definition may be still undecided, but one thing is for sure: inhumane strandings over the course of such a long period time have caught the environmental community’s attention, and as research like at MGEL continues to take place, further action to protect species like beaked whales from human disturbance is inevitable.
Information and figures from talk taken from: Schick et al. “Accounting for Positional Uncertainty When Modeling Received Levels for Tagged Cetaceans Exposed to Sonar.” Aquatic Mammals, 2019.