Undergraduate Researcher – Geospatial Ecology of Marine Megafauna Laboratory

Daily Diel Ins! Calling patterns of New Zealand blue whales

Alana Cary, St. Mary’s College of Maryland Undergraduate in Marine Science, 2026 NSF REU and GEMM Lab SAPPHIRE Project Intern

Hello everyone! My name is Alana Cary, and I was one of the NSF REU interns with the GEMM Lab this summer. I am currently in my senior year at St. Mary’s College of Maryland (SMCM), where I study Marine Science. Growing up along the Chesapeake Bay, I was always captivated by the connection between people and marine ecosystems. That curiosity led me to pursue marine mammal ecology, and this summer I had the amazing opportunity to travel across the country and dive into bioacoustics research with the GEMM Lab at Oregon State University’s Hatfield Marine Science Center.

My project, Daily Diel Ins: Investigating Diel and Seasonal Calling Patterns of New Zealand Blue Whales, explored how the world’s largest animals use sound over the course of the day and throughout the year. Working under the mentorship of Dawn Barlow and Leigh Torres, I spent ten weeks immersed in whale calls, coding, and a lot of matcha (shoutout to RISE cafe!).

Figure 1. Picture of me (Alana C) at Devils Punchbowl my first week in Oregon.

Why study whale voices?

Blue whales (Balaenoptera musculus) are record-breakers: the largest animals to have ever lived, producers of the loudest biological sounds, and yet, surprisingly elusive. They spend most of their lives far beneath the surface, only surfacing briefly to breathe. This lifestyle makes them difficult to study visually. But blue whales leave behind something extremely powerful — their voices.

Baleen whales rely heavily on low-frequency sounds to forage, navigate, and communicate across vast distances (Clark & Ellison 2004). New Zealand blue whales are unique since they produce a distinct regional song (Torres et al. 2013; Barlow et al. 2018), and their calls provide insight into both foraging and reproductive behavior.

Blue whales produce two main call types (Figure 3):

Songs – long, stereotyped sequences produced by males, likely used in reproduction and communication.
D calls – short, frequency-modulated downsweeps produced by both sexes, often linked to foraging or social behavior.

Previous research has described the seasonal calling patterns of New Zealand blue whales (Barlow et al. 2023), but until now, diel (day–night) patterns had not been studied. This is important because blue whales’ primary prey, krill, perform diel vertical migration (DVM) in many parts of the ocean — ascending at night and descending during the day. If whale calls are tied to foraging or social interactions, they might vary depending on these light-driven prey movements.

Listening to giants: methods and workflow

**Figure 2.** Map of Rockhopper hydrophone deployments in the South Taranaki Bight, New Zealand. Stars mark the Rockhopper east (RH-east) and west (RH-west) recording sites. Bathymetric contours are drawn at 100 m intervals.

My study focused on the South Taranaki Bight (STB), a productive upwelling region between New Zealand’s North and South Islands. The STB supports a unique population of blue whales year-round, providing foraging and reproductive opportunities (Torres et al. 2013; Barlow et al. 2018), but it is also an area with heavy human activity, including shipping, oil and gas, and fishing. Understanding when and how whales call here helps identify times of overlap with disturbance.

Here’s how I studied their voices:

Hydrophones in the field – We used Rockhopper autonomous hydrophones, which are compact devices designed to record low-frequency sound for long periods (Klinck et al. 2020). These instruments collected a year of acoustic data in the STB (January 2024–January 2025).
Manual annotation – From this massive dataset, one day was randomly selected from every two weeks (24 days total) and I manually annotated spectrograms of songs and D calls in Raven Pro. I identified songs in the 0–75 Hz band and D calls up to 150 Hz, following published criteria.
Machine learning classification – These manual annotations were used to evaluate a BirdNET machine learning model (Kahl et al. 2021) trained to detect whale calls. The model then predicted calls across the entire year-long dataset.
Validation – Because D calls are harder to classify, I manually reviewed all predicted D calls to remove false positives. Song detections, which had extremely high precision and recall, were kept without this extra step.
Binning into diel phases – I aggregated call detections by hour and used the suncalc R package (Thieurmel et al. 2022) to assign diel phases (day or night). I also grouped calls by month and season to evaluate seasonal trends.
Statistics in RStudio – To test whether month, diel phase, or their interaction influenced call rates, I ran two-way ANOVAs with post hoc Tukey’s HSD tests for pairwise comparisons

**Figure 3.** A spectrogram showing two distinct call types produced by New Zealand blue whales. The green box highlights the repetitive, low-frequency *song*, while the blue box highlights a short, frequency-modulated *D call*. Time is on the x-axis (hh:mm:ss) and frequency (Hz) on the y-axis

Results: different rhythms for different calls

The results revealed that songs and D calls follow very different patterns.

Songs – Seasonal, weakly diel:

Songs showed strong seasonal variation, peaking in late summer and autumn (February–May).

Diel effects were weaker but significant: slightly more daytime calling, consistent across months.

This suggests that songs are driven mainly by reproductive cycles, not daily light cues.

**Figure 4.** Monthly variation in New Zealand blue whale song detections from January 2024 to January 2025, separated by diel phase (day vs. night). Songs peaked in late summer and autumn, consistent with reproductive timing. Diel differences were minimal, with slightly more daytime calling

D calls – Both seasonal and diel:

D calls showed highly significant effects of month, diel phase, and their interaction.

Calling rates peaked in spring and summer, with more D calls during daytime hours.

The diel effect varied by month: some months showed strong differences between day and night, while others showed none.

This suggests that D calls track foraging, responding to increased krill availability during spring and summer months, and krill’s diel vertical migration

**Figure 5.** Monthly variation in New Zealand blue whale D call detections from January 2024 to January 2025, separated by diel phase (day vs. night). Peaks occur during spring and summer, with more daytime calling during these seasons. This pattern suggests D calls are closely tied to foraging opportunities on krill.

Why does this matter?

Understanding when whales call is more than an academic exercise. The South Taranaki Bight is not only an important whale habitat, it’s also a busy human space. By identifying when whales are most acoustically active, we can better understand potential conflicts with anthropogenic noise from shipping or industrial activities. For example, the fact that daytime D calls peak in spring and summer, times of high foraging effort, means that increased vessel noise during these periods could disrupt critical feeding-related communication. This kind of fine-scale temporal knowledge can inform management strategies to reduce human impacts on a vulnerable whale population. These insights also feed into the GEMM Lab’s SAPPHIRE project goal: linking oceanography, prey dynamics, physiology, and acoustics to understand how blue whales respond to a rapidly changing ocean (Barlow & Torres, 2021; Barlow et al., 2023).

Reflections on my REU journey

When I first arrived at Hatfield, I had never worked with passive acoustic data before. At first, spectrograms just looked like fuzzy TV static. But every day I learned to trust the process. Soon, I was able to fly through annotations and recognize calls without even seeing them on the spectrogram— just listening. I remember creating my plots and seeing the clear diel patterns, I couldn’t help but grin.

**Figure 6**. Dawn, Leigh, and I at the Coastal Intern symposium after I finished presenting my final research poster.

There were some moments that were frustrating as well, like when my entire selection table would delete and I’d have to start over, or debugging the same error message with no hope of figuring it out. But these frustrations taught me to be patient, persistent, and to not be afraid to ask for help. Weekly check-ins with Dawn pushed me to put my critical thinking to the test to decipher what my results meant. My co-interns and lab mates provided laughter, support, and encouragement that made the work even more rewarding. Beyond the data, I also learned how science is built on community. Research isn’t just all about running tests and analyzing plots, it’s about sharing ideas, collaboration, and building on each other’s work.

**Figure 7.** Alana and Bennie the Banana Slug at Cape Perpetua after a hike.

As a first-generation college student, this opportunity showed me that I can belong in marine science. I leave this summer with new skills in bioacoustics, statistics, and science communication, but also with a deeper sense of confidence and belonging in research.

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References

Barlow, D. R., Klinck, H., Ponirakis, D., Branch, T. A., & Torres, L. G. (2023). Environmental conditions and marine heatwaves influence blue whale foraging and reproductive effort. Ecology and Evolution, 13(2), e9770. https://doi.org/10.1002/ece3.9770

Barlow, D. R., & Torres, L. G. (2021). Planning ahead: Dynamic models forecast blue whale distribution with applications for spatial management. Journal of Applied Ecology, 58(11), 2493–2504. https://doi.org/10.1111/1365-2664.13992

Barlow, D. R., Torres, L. G., Hodge, K. B., Steel, D., Baker, C. S., Chandler, T. E., Bott, N., Constantine, R., Double, M. C., Gill, P., Glasgow, D., Hamner, R. M., Lilley, C., Ogle, M., Olson, P. A., Peters, C., Stockin, K. A., Tessaglia-Hymes, C. T., & Klinck, H. (2018). Documentation of a New Zealand blue whale population based on multiple lines of evidence. Endangered Species Research, 36, 27–40. https://doi.org/10.3354/esr00891

Clark, C. W., & Ellison, W. T. (2004). Potential use of low-frequency sounds by baleen whales for probing the environment: Evidence from models and empirical measurements. In Echolocation in Bats and Dolphins (Vol. 1–1, pp. 564–589). Univeristy of Chicago Press.

Kahl, S., Wood, C. M., Eibl, M., & Klinck, H. (2021). BirdNET: A deep learning solution for avian diversity monitoring. Ecological Informatics, 61, 101236. https://doi.org/10.1016/j.ecoinf.2021.101236

Klinck, H., Winiarski, D., Mack, R. C., Tessaglia-Hymes, C. T., Ponirakis, D. W., Dugan, P. J., Jones, C., & Matsumoto, H. (2020). The Rockhopper: A compact and extensible marine autonomous passive acoustic recording system. Global Oceans 2020: Singapore – U.S. Gulf Coast, 1–7. https://doi.org/10.1109/IEEECONF38699.2020.9388970

Thieurmel, B., & Elmarhraoui, A. (2022). suncalc: Compute sun position, sunlight phases, moon position and lunar phase (Version 0.5.1) [R package]. Comprehensive R Archive Network (CRAN). https://CRAN.R-project.org/package=suncalc

Torres, L. (2013). Evidence for an unrecognised blue whale foraging ground in New Zealand. New Zealand Journal of Marine and Freshwater Research, 47(2), 235–248. https://doi.org/10.1080/00288330.2013.773919

Exploring the Western Antarctic Peninsula

By Abby Tomita, undergraduate student, OSU College of Earth, Ocean, and Atmospheric Sciences, research intern in the GEMM and Krill Seeker Labs

This February, during the winter term of my third year at Oregon State, I was presented with a once-in-a-lifetime opportunity. After spending the last year studying the zooplankton krill as part of Project OPAL, I was invited to spend the austral winter season doing research on Antarctic krill (Euphausia superba) under supervision of experts Dr. Kim Bernard and PhD student Rachel Kaplan. Additionally, we were lucky enough to participate in two research cruises along the Western Antarctic Peninsula (WAP).

Figure 1. Sailing into the sunset on the RV *Laurence M. Gould*.

Unsurprisingly, it is no easy feat getting to the bottom of the world. After an incredibly thorough physical qualification process and two days of air travel from Portland, Oregon, we reached the lovely city of Punta Arenas, Chile. It was such a relief to arrive – but we were only halfway there. The next portion of our trip was the one that I was most anxious about, especially as someone who is prone to seasickness: crossing the Drake Passage. This stretch of the ocean, from the southernmost tip of South America to the Antarctic Peninsula, is notoriously treacherous as water in this area circulates the globe completely unobstructed by land masses. I soon learned the value of scopolamine patches and nausea bracelets, which helped me immensely through this five day journey. From Punta Arenas, we boarded the RV Laurence M. Gould, along with a seal research team from the University of North Carolina Wilmington. They were headed down south to look for crabeater seals to better understand not only their physiology, but also their role in the trophic ecology of the WAP.

The Passage was rough, but not as terrible as I expected. The hype around it made me think I’d be faced with something as menacing as the giant wave from The Perfect Storm, and while the rocking and rolling of the ship was far from pleasant, my nausea aids, as well as the amazing people and vast selection of movies on board made it manageable. Despite being extremely nervous for the Passage, I was also very excited to celebrate my twenty-first birthday during it. It was a memorable, although untraditional birthday experience that was made all the more special by my friends on the ship who took the time to celebrate the day as best as we could.

Figure 2. Taking in the sights of the Neumayer Channel with Kim!

The morning that we reached the Bransfield Strait was something truly unforgettable. Up until that point, I knew our destination was Antarctica, but I couldn’t really wrap my head around it because it was such a distant place and concept to me. I remember walking out onto the starboard side of the second level deck and seeing huge mountains out in the distance. For some reason, I had never considered how massively tall the mountains of the peninsula are, and just the fact that there were mountains down here at all. I joined the others at the bow, where we stood for hours in awe at the first land we had seen in days. Though many of the other scientists and crew members on board had been to this icy continent before, this was my first time, and I was in a state of disbelief. We’d finally made it and it sunk into me that I was in Antarctica, and that I would be here for the next five and half months.

After a day of hiding from strong winds in the Neumayer Channel, we were able to dock at Palmer Station (the smallest of the three US research bases in Antarctica) for our first port call, and seeing Palmer for the first time was just as exciting as seeing the continent. It looked so small at first, especially with the glacier and mountains looming behind it. Once the ship was tied up, orientation began. The station manager came onto the ship to give us an overview of what we could expect on station and the general Palmer etiquette. Next, we were given a tour of the facilities, from the lab spaces and aquarium room, up through the galley/dining area, past the hot tub and sauna, and into the lounge and bar in the GWR (Garage, Warehouse, and Recreation) building. I was surprised at how cozy the station was on the inside. In pictures, the buildings’ exteriors looked similar to the outside of a metal shipping container, but the inside was welcoming and warm. Those of us staying on station then sat through several hours of a more detailed orientation that somehow wore us out despite sitting in comfy recliner sofas the whole time. After sleeping on the rocking ship for about a week, I had some of the best sleep of my life that first night at Palmer Station.

Figure 3. Arriving at the Palmer Station pier in the first morning light.

Our first research cruise started a few days after arriving at Palmer, and just like that, we were off to explore the Southern Ocean. This leg of the trip took us south, down to Marguerite Bay and the region of Alexander Island, for ten days. The views were just spectacular everywhere we went, and it was so humbling to step out onto the deck to see gigantic mountains all around the ship. By day, us “krillers”, as our team is known, camped out on the bridge of the ship with the seal team, where we looked for sea ice floes with lounging crabeater seals. By night we conducted CTD casts, filtered water for chlorophyll, and deployed nets to catch our favorite tiny crustacean critters, along with any other zooplankton in our track. Unfortunately for both our group and the seal team, many areas that we visited were not frequented by krill or crabeater seals, though the seal team did successfully study and tag one seal over the course of the first cruise.

Figure 4. Rachel (right) and I (left) filtering water for chlorophyll on the LMG.

One of the highlights of this leg of the cruise was our Crossing Ceremony, as we’d crossed the Antarctic Circle (approximately 66.5ºS) shortly after leaving Palmer station. Myself and six others were crossing for the first time, so to earn our “Red Noses”, we had to pay tribute to King Neptune and his court. It would not be a Crossing Ceremony without at least some light pranking, so when they brought us out individually to the main deck, I knew something was coming our way.

Figure 5. Taking a celebratory picture with King Neptune’s court…with a surprise after.

The ten days flew by, and when we arrived back on station, we had less than a week to prepare for our next excursion on the LMG, which would be fifteen days. The time back at Palmer went quickly as we organized our lab space and entered data from the first cruise. The ship came back once more and we were off, this time heading north along the Peninsula to the Gerlache Strait. The sights were as breathtaking as ever, and I was excited to be back with my friends from the ship.

Figure 6. Kim (left) and I (right) pour krill we caught into an XACTIC tank.

Our first day of transit was through the Lemaire Channel, one of the most stunning areas that we passed through (check out the photo gallery at the end of this post!). We spent the majority of the day on the bow and the deck of the bridge taking in the beautiful towering mountains on either side of the narrow channel and watching for penguins and humpbacks, of which there were many. This voyage segued into an extremely productive night of science for us where we caught thousands of krill that we were able to keep live in tanks on the ship, in preparation for later use for our experiments on station. Our first productive night of science was auspicious for the rest of the cruise as we caught and processed thousands more krill, and the seal team had a much more fruitful experience finding crabeater seals (they found/worked on 8 seals and named them all after fruits!). The highlight of this second cruise for me was getting to accompany the seal team onto an ice floe in the Lemaire Channel to assist them in their work on the crabeater, a female juvenile who they named Mango!

Figure 7. Watching Mango’s nose to calculate and record her breaths per minute (US NMSF Permit #25770).

Returning to Palmer for the final time on the LMG was just as exciting as arriving the first time, especially with the knowledge that we’d have one last night of celebration with our friends from the ship at the Cross Town Dinner – a night to celebrate the solstice with both the Palmer crew and LMG crew. Although the dinner and subsequent party were a blast, I felt a lingering sadness knowing that the majority of the people I spent almost two months with would be heading north, back to their respective homes while Kim, Rachel, and I stayed at Palmer for the next few months. The next day, after saying our goodbyes, the three of us stood on the Palmer pier with tears streaming down our faces, waving frantically at the ship to our friends on the deck. In spite of my sadness, I knew that the coming months would be a thrilling series of new experiences in one of the most magical and special places that I have ever had the pleasure of being in.