“Trying to tag large, powerful animals that are continuously moving and diving beneath the surface of the water, which has tides, waves, swells —while sometimes in the wind or rain or with glare from the sun impairing our ability to follow the whales — makes for a really difficult time!” Tennessen says. “It is rarely the case that we get a tag on immediately. More often, the stars don't align for several hours, which can be quite frustrating.”

The tagger stands near the bow of the boat with a carbon fiber pole 20- to 30-feet long, a DTag at the end.

“When the whale is close enough, the tagger in a quick motion [slaps] the pole down and when the tag touches the whale’s back, it pops off of the pole and sticks to the whale. Typically it stays after that, [but] sometimes they do fall off immediately,” Tennessen says. While the tags usually fell off after about eight hours, these days they can stay on for up to 24, she says

Once they fall off, the tags float to the surface and broadcast a signal so that the team can recover them from the ocean.

The team measured every dive that went at least one meter deep. With 13 orcas’ worth of data, they applied a pattern-finding algorithm based on two types of echolocation (buzzing and clicking) and four movement variables to identify different “behavioral states,” or types of dives.

Discovering the ins and outs of orca foraging

Through this noninvasive suction cup technology, researchers discovered new findings about orca feeding behavior.

The algorithm revealed orcas have five diving activities: shallow searching for prey, with echolocation; intermediate dives with some echolocation; deep prey pursuits — “picture being on a roller coaster ride with lots of erratic movement, echolocation and buzzing,” Tennessen says — and the low-movement, low-sound activities of both shallow-water breathing and traveling. Some of these states are decipherable only by detecting the acoustic recordings of echolocation, which only the DTag can provide.

The data also reveal how, for orcas, the hunt starts well before the big chase.

“Foraging behavior isn’t just a dive to grab a salmon,” Tennessen says. It starts out with a prolonged period of searching with echolocation near the surface, followed by a deeper dive or a “beeline” straight down to catch the fish. After that, behavior varies: Orcas come back to the surface to breathe and rest, and they continue foraging or they switch to another activity, like traveling.

These behaviors don't appear to stem from spontaneous decisions: When orcas commit to a hunting behavior, they stick with it.

“Whales aren't just randomly chasing the fish here or there,” Tennessen says, “which would suggest that there's something important driving that behavior.” Possible explanations are that orcas employ groupwide decisions, or make choices based on the availability of salmon. But the “why” of these hunting behaviors being “clumped in time” is still unclear.

“We don't exactly know what's driving this pattern, but it was interesting to see that when it's time to hunt, they hunt and they do it for a while and then they rest and then they rest for a while and then they might travel.” Tennessen says.

That there’s a method to hunting underscores the potential consequences of disturbance, she says. “If there is a right time to do something like hunting … whales may be particularly vulnerable to disturbance during these foraging periods, especially if the whales can’t simply wait until the disturbance ends because they would miss important foraging opportunities,” she says. “Activities that could interfere with hunting could be detrimental” at many points during the hunting process.

The research also showed further insight into sex-based hunting styles. Males spent more time searching for and chasing salmon than females, who spent more time traveling and socializing.

That may come down to males’ greater energy requirements, Tennessen says. “Alternatively, females’ time might be constrained because of other duties, like caring for calves. This means that disturbance could potentially have a greater impact on females if their already-limited foraging opportunities are further impaired. We are currently studying this further.”

More foraging research is on the way

This new work is setting up the team to do critical analysis of whether human activity impacts foraging success.

“[Here], we didn't show that disturbance is affecting foraging. But we pave the way for being able to do that soon,” Tennessen says. “Now that we understand what [foraging] looks like, we can start asking, how does the presence of vessels affect foraging outcomes? Do whales seem to be less likely to catch fish when a lot of vessels are present or when noise is elevated, or other factors like that?”

That’s exciting to Gaydos. “We actually know a lot about these animals, and I feel like we were able to make a lot of recommendations that were based on really good science,” he says. “[But] one of the challenging [things] for us was this question about noise in vessels and vessel interference.”

That was a hard discussion, he says, because everyone at the table recognizes the value of whale watching, both economically and as a way to introduce people to orcas.

“I think this is the sort of data that's going to help us in the long run understand, where can we have boats? How do we have boats there? How many boats do we have there?” Gaydos says.

To better determine whether the plight of the southern residents is unique to themselves, Tennessen says, NOAA is comparing this information to similar data from northern residents..

“The northern residents, while still endangered, have continued to grow over the same period of time that the southern residents have been declining,” Tennessen says. “And so we're trying to understand if differences in foraging behavior could be related to that, or if differences in the disturbances that they experience and the potential impacts of those disturbances on foraging could potentially explain population decline as well.”

This method of tagging will likely inform future research and conservation efforts. For instance, Tennessen and her colleagues have begun a three-year tagging study to collect overnight whale data that can address a gap in our foraging knowledge.

Gaydos reinforces that continued research is as important as action.

“I think what people have to remember,” he says, “is it's still important — even though we're taking actions for recovery — to continue to do science to learn things and to measure if the actions we've taken have made a difference.”

Update: This article was updated at 11:09 a.m. on Oct. 24, 2019, to correct the relationship between the journal Scientific Reports and the journal Nature; and to reflect updated information from the research team about the number of whales' data involved in the study.