By Rachel Kaplan
Fall/Winter 2022
Editor’s note: Rachel Kaplan is a Ph.D. student in the College of Earth, Ocean, and Atmospheric Sciences and the Department of Fisheries, Wildlife, and Conservation Sciences. She is co-advised by Kim Bernard and Leigh Torres, studying the relationship between krill and whales, and occasionally blogging about her experiences.
I always have a small crisis before heading into the field, whether for a day trip or a several-month stint. At first, I’m dying to go — up until the moment when it is time to leave. Then I decide I’d rather stay home, keep working on whatever has my current focus and not break my comfortable little routine.
Preparing to leave on the May 2022 northern California Current cruise was no different. And, as usual, a few days into the cruise, I forgot about the rest of my life and normal routines, becoming totally immersed in the world of the ship and the places we went. I learned an exponential amount while away. Being physically in the ecosystem that I’m studying immediately had me asking more, and better, questions to explore while at sea and bring back to land.
Many of these questions and realizations centered on predator-prey relationships between krill and whales at fine spatial scales. We know that distributions of prey species are a big factor in determining where whales are found in the ocean, and one of our goals on this cruise was to observe these relationships more closely. The cruise offered an incredible opportunity to experience these relationships in real time: While my labmates, Dawn and Clara, were up on the flying bridge looking for whales, I was down in the acoustics lab, watching incoming echosounder data to identify clusters of krill.
We used radios to stay in touch and report what we were each seeing, learning quickly that we tended to spot whales and krill almost simultaneously. Experiencing this coherence between predator and prey distributions felt like a physical manifestation of my Ph.D. It also affirmed my faith in one of our most basic modeling assumptions: that the backscatter signals captured in our acoustic data reflect the preyscape experienced by nearby whales.
Being at sea with my labmates also catalyzed a synthesis of our different types of knowledge. I usually focus on whether a certain type of whale is present or not while surveying. But Clara, with her research focus on whale behavior, thinks in a completely different way. She timed the length of dives and commented on the specific behaviors she noticed, bringing a new level of context to our observations. Dawn, who has been joining these cruises for five years now, shared her depth of knowledge built through repeat journeys, helping us understand how the system varies through time.
One of the best experiences of the cruise was when we conducted a targeted net tow in an area of foraging humpbacks off the central Oregon coast near Heceta Head. The combination of the krill signature I was seeing on the acoustics display, and the radio reports from Dawn and Clara of foraging dives, convinced me that this was an opportunity to see exactly what zooplankton was in the water near the whales. Our chief scientist, Jennifer Fisher, and the ship’s officers worked together to quickly turn the ship around and get a net in the water.
The opportunity enabled me to test my interpretation of the acoustics data and compare what we captured in the net with what I expected from the backscatter signal. Just as I had hoped, we caught the two krill species I am studying, Euphausia pacifica and Thysanoessa spinifera, and I was able to collect samples for caloric analysis.
Ecosystem modeling gives us the opportunity to untangle incredible complexity and put dynamic relationships in mathematical terms, but being out on the ocean provides the chance to develop an intuitive feel for these relationships. I’m so glad to bring this new perspective to my next round of models, and excited to continue trying to tease apart fine-scale dynamics between whales and krill.
