September 2024
“Alright, this is gonna be the one!” The 22-foot inflatable research vessel Balena speeds up and approaches a group of four humpback whales along the edge of Stellwagen Bank National Marine Sanctuary offshore Provincetown, Massachusetts. “A little closer! Closer!” There’s a brief silence in the air—everyone seems to be holding their breath as we wait for Sanctuary Scientist Mike Thompson to extend the pole far enough for the tag to stick to the back of the humpback whale. Just as the whale begins to arch its back to do a deep dive, the four suction cups on the tag adhere to its skin. The whale’s large black and white tail flicks above the water’s surface, then the massive animal disappears beneath the murky water.
This whale’s name is Azrael. We know this from a photo identification database that allows researchers to identify and name individual whales based on unique features on their tails. Patterns develop from natural pigmentation, scarring from predators or other wildlife encounters, and from interactions with humans (e.g., entanglement in fishing gear). Another whale swimming in Azrael’s group was tagged that day too—it’s name is 3.14 because it has what resembles a pi symbol (π) on the left lobe of its tail.
Whale “Caller ID”: Innovative Tags
“In order to study anything, you have to have the right tools to observe it,” Thompson explains. The tags used on Azrael and 3.14 are called DTAGs (digital acoustic recording tag), and they are a non-invasive tool that uses suction cups, which adhere to the whale’s back for up to 40 hours, and then separate from the whale during intense surface activity (such as breaching), when the air tube in the instrument corrodes over time, or when a preprogrammed electronic signal corrodes a link and releases the tag.
“These tags record the animals pitch, roll, and heading, and also record any sounds they make or hear,” says Dave Wiley, the research coordinator at Stellwagen Bank National Marine Sanctuary. The tags are also equipped with GPS units to observe what the animals are doing relative to their environment and location.
There have been four generations of DTAGs since they were first developed in 1998 at Woods Hole Oceanographic Institution, with decreasing size and increasing capabilities each generation. DTAG-4 is the latest version that is being used and tested by the team, and is small enough to hold in the palm of your hand.
All of this detailed information about individual whales collected over many years is being used for conservation biology. “The top 10–15 meters of the ocean is the most dangerous for whales passing through shipping areas,” says Dana Cusano, a bioacoustician and behavioral ecologist at Syracuse University. As shipping traffic increases, whales, which already face issues related to climate change and entanglement in fishing gear, are at an increased risk of being struck by large vessels. “With the data from these newer tags, we can identify areas where whales are at a higher risk and make informed decisions to help protect them from the threat of ship strikes,” Cusano adds.
These newer tags also provide fine-scale information about the sound range and behavior of whale species. When whales pass by stationary passive acoustic monitoring devices in the ocean, an underwater microphone records their song and vocalizations. However, this passive acoustic data is not fine-scale enough to know which individual in a group of whales is making those sounds. In 2022, Cusano, Wiley, and colleagues tagged 12 endangered sei whales in the first ever study using acoustic tags to document the calling behavior of sei whales in feeding grounds. The success of this study shed light on the usefulness of this particular tagging technology to identify which individual animal is calling.
Taking this a step further, the team is now using “group tagging”—a method of tagging multiple individuals from a single group to distinguish which animal is making specific vocalizations.
To date, biologging tags have provided important information for many species of large whales, including humpback (Megaptera novaeangliae), blue (Balaenoptera musculus), sperm (Physeter macrocephalus), sei (B. borealis), North Atlantic right (Eubalaena glacialis), fin (B. physalus), and minke (Balaenoptera acutorostrata) whales.
Advancements in How Whales are Tagged
Traditionally, both DTAGs and CATS (customized animal tracking solutions) have been applied by a person holding a 30-foot pole with the tag attached at the end, and tapping the tag down onto the whale. This requires some highly skilled maneuvering by the small boat operator, good balance, aim, and timing by the tagger, and excellent communication between the team aboard the vessel throughout the process.
“As the vessel operator, you don’t want to hang back too far, because the pole won’t reach and you’ll miss, but if you get too close the situation can become dangerous for the tagger up on the bow if that whale tail hits them,” explains Wiley.
Researchers wanted to devise a way to minimize disturbance of the whales while collecting data, so Ocean Alliance came up with the idea of using an uncrewed aerial system, or drone, to drop the tags down onto their backs.
Watch video: Tagging Humpback Whales
“This is the first major improvement dealing with how the animals are approached, and this way we don’t have to get as close to them,” says Wiley. In addition to maintaining a safe distance from the whales, relying on drones to tag large whales provides major advantages such as speed, maneuverability, and a bird's-eye view. This allows the drone pilot to hover over the focal whale while it swims subsurface, maintaining an optimal target position until the whale surfaces again.
“Our team has been working and sharing data with Ocean Alliance, and when we tag one or two whales in a group, sometimes they’re able to come in and tag another in the group with the drone to get the data we need,” adds Wiley. This helps to minimize repeated disturbances of the same group of whales.
Chris Zadra, the director of drone programs at Ocean Alliance adds that “Ocean Alliance is proud to use our unique skill sets and newly developed methodologies to aid NOAA in the collection of these critically important datasets. It’s exciting to have developed a system that works across multiple species and field environments and that is already proving to have a positive impact on the world of marine mammal research.”
According to Zadra, as the systems and methodologies continue to be further developed, Ocean Alliance’s goal is to eventually make them more widely available for research efforts across the globe. The Stellwagen Bank National Marine Sanctuary research team hopes to eventually get their own drone to use for whale tagging fieldwork.
So how exactly does dropping a tag from a drone work, and why doesn’t the tag land upside-down?
“When the tags are dropped by a drone, there is a 3D printed fin at the top to help guide the tag down gently, similar to how a lawn dart works,” said Ethan McMillan, research engineering specialist at University of Michigan. Gravity from the fall allows enough pressure for the tag to stick, and there is a trigger mechanism that causes the fin to release once the tag is suctioned.
Both approaches (pole and drone tagging) have their virtues and their drawbacks, which is why it’s ideal to have the available equipment and staff training to utilize both techniques. On one hand, drones are less invasive to the whales and offer more speed and maneuverability, while on the other hand, drones have limitations such as not being able to fly in high wind or in “no drone zones” that the whales may enter.
What We’ve Learned This Season
Each year, researchers learn more about whale behaviors. According to Laura Howes, outreach specialist and field researcher at the sanctuary, “This year we have been able to document lunge feeding behavior on a different type of prey fish [mackerel], which is a behavior we have not been able to focus on much previously. We were also able to successfully tag all members of one group and track every behavior the tagged animal does at the surface.”
Howes adds that tagging all the whales in one group also allows acoustic researchers to understand how each individual communicates within the group.
Previous years of tagging data have revealed information about behaviors such as bubble net feeding patterns and bottom feeding techniques (singly, in pairs, and in triads). Bottom feeding has provided proof of "handedness" in humpback whales, showing that more are "righties" than "lefties." Multiple tags have shown cooperative feeding and poaching behaviors. Sound recordings have revealed that male humpbacks sing partial songs in northern feeding grounds and that some whales use unique clicking/buzzing sounds, labeled "megapclicks" or patterned pulses of sound (paired bursts) for nighttime feeding. Tags equipped with video have also shown nursing behavior between a mother and calf and provided insights into the timing of this behavior.
The multi-year project (initiated in 2004) is a collaboration among researchers from Stellwagen Bank National Marine Sanctuary, NOAA Fisheries (Greater Atlantic Regional office and Northeast Fisheries Science Center), Woods Hole Oceanographic Institution, University of New Hampshire, Center for Coastal Studies, International Fund for Animal Welfare, UC Santa Cruz, Syracuse University, Stanford University, University of Michigan, and many more.
Rachel Plunkett is the content manager and senior writer at NOAA’s Office of National Marine Sanctuaries