Written by Gussie Hollers
Warm Springs bay in June
This summer, I was very lucky to be able to spend two months with the Alaska Whale Foundation (AWF) to deploy Customized Animal Tracking Solutions (CATS) suction-cup tags on humpback whales. This tag data, paired with data from Unoccupied Aerial Systems (UAS, drones), will help us better understand the energy budgets of whales using different foraging strategies. The goal of the third chapter of my dissertation is to quantify the energetic costs and benefits of various foraging strategies, to understand how changes in behavior could affect the health of individuals and the population. This data is also part of our lab’s larger project quantifying humpback whale bioenergetic demands in the face of climate change and shifting prey availability.
A large portion of the whales we see in Hawaiʻi spend the summers in Southeast Alaska eating enough herring, krill, and other small fish to survive two migrations and a winter spent fasting. Southeast Alaska is an important feeding ground for the North Pacific humpback whale population, and has been heavily impacted in recent years by marine heatwaves. The humpback whale population and birth rate declined sharply during the 2014-2018 heatwave, underlining the importance of studying their individual and population health.
This whale breached for over 30 minutes close to our boat, which made it not a good candidate for tagging! Video taken by Liah McPherson
Humpback whale foraging strategies
Southeast Alaska is a dynamic ecosystem, with prey type, location, and abundance changing throughout the summer. In the early summer, humpback whales take advantage of the herring and juvenile fish congregating close to shore. In the mid to late summer, most humpback whales shift to eating krill.
Humpback whales are unique among baleen whales because they have developed a range of bubble net tools to help them exploit different species and densities of prey. The most common type of foraging strategy for rorquals (humpbacks, blue whales, minkes, etc.) is lunging through patches of prey deep underwater, but humpback whales are creative and their bodies are uniquely shaped, allowing them to feed on various types of prey in different ways.
One of the most famous Southeast Alaska foraging strategies is the cooperative bubble net feeding on herring. Groups of 5-20 whales will feed together, with one whale blowing a bubble curtain to corral the herring, and another whale making a siren call to scare the herring into denser schools. The whales will all swim up together, pushing the herring toward the surface, and lunge in a tight group. Seeing the bubble netting close to the surface was definitely one of my favorite parts of fieldwork this summer!
A group of whales lunging at the surface while cooperatively feeding on herring. Video taken by Jess McCoppin
Video from a CATS tag of a whale blowing a bubble net in a cooperative feeding group. At the end, two whales lunge in view of the camera
Solitary humpback whales also use bubble net tools to feed on sparse patches of krill. The bubble nets condense the krill, making each lunge more efficient. To learn more about this strategy, Andy, Will, and Lars (and co-authors) recently published a paper on these krill bubble nets – check it out here!
Figure 1 from the Szabo et al. 2024 paper showing the variables and data collected from drones and CATS tags to analyze the bubble nets.
From figure caption: (a) UAS-derived bubble-net metrics for a two-ring bubble-net, including the area and diameter for the inner ring, and the horizontal inter-bubble distance (i.e. mesh size) for the outer ring. (b) Whale-producing bubble pulses, showing (i) left flipper, (ii) previous bubble pulse and (iii) new bubble pulse. (c) Whale with mouth open immediately prior to a lunge, with (iv) top jaw, (v) baleen rack, (vi) bottom jaw and (vii) right flipper visible. (d) Whale approaching the surface after a lunge, with the (viii) mouth closed prior to breaking the water’s surface and (ix) full bubble-net visible.
Another interesting bubble net strategy is used by whales on juvenile fish or krill right up against the rocky shore. The whales blow a small ring of bubbles also to condense the prey. This strategy has become more common with the release of commercial salmon smolt in the late spring. We were lucky enough to see a whale doing this right next to our boat in the cove where we were anchored one night.
Drone video of a whale using a bubble net to feed close to shore on small fish or krill. Video taken by Lewis Evans
These strategies all have different costs and benefits, for example, cooperative bubble net feeding on herring might be more energetically costly than lunging on krill because of the time and extra movement needed to create a bubble net. But herring has more energy than krill, so that strategy might be more advantageous at certain locations and times of the year. By measuring the amount of energy each strategy uses, and approximating how much energy each strategy gains, we can better understand how a whale might choose one or the other to optimize net energy gain.
Our study area
The main research program at AWF is the Ocean Health Program: systematically monitoring the whale population and oceanography of Southeast Alaska. AWF conducts surveys of most of the inside waters of Southeast Alaska, doing distance sampling, photo-ID, drone body condition, and taking oceanographic measurements. The field team goes out for up to 4 days at a time to reach the farther points of the survey area.
Map from August 2023 of the AWF study area blog showing all the systematic survey points (black triangles) and whale density (red dots). Map made by Dana Bloch
This was a summer of “first times” for me: visiting Southeast Alaska, spending a night on a boat, seeing brown bears and salmon, tasting an iceberg, and watching humpback whales cooperatively bubble net feed. The Alaska Whale Foundation field station is in a remote bay on the western coast of Baranof Island, accessible by boat 4 hours away from the nearest (tiny) airport. I loved being able to swim in Baranof lake, pick blueberries, and bathe in the natural warm springs. Alaska was even more beautiful than I expected, and I am grateful for the time I had to get to know the land and ocean.
Pictures from around Warm Springs Bay: the boardwalk down to the dock in June, blueberry picking in August, the view from the hot springs baths, and a calm early morning leaving the bay
Our goals, challenges, and highlights
Our goal this summer was to tag whales using different foraging techniques. We focused on tagging whales in cooperative bubble net groups feeding on herring in June in Tebenkof Bay, and solitary whales feeding on krill in August in Frederick Sound and Chatham Strait.
We tagged a total of 17 whales, 9 cooperative bubble net hunters in June, and 8 solitary krill foragers in August.
June stats:
2 tagged whales were bubble blowers
80 hours of data total, average deployment duration of 9 hours
August stats:
2 tagged whales were strategy switching between krill bubble netting and deeper lunging
2 whales tagged off Point Gardiner, 6 tagged in Chatham Strait by Angoon
45 hours of data total, average deployment duration of 5.5 hours
In June, we worked with nature filmmakers Florian Schulz and Shane Moore to get tag and drone videos of humpback whales for an upcoming nature documentary. We anchored for four nights in Tebenkof Bay, and Lewis and I enjoyed kayaking around the coves at sunset looking at seals and jellyfish. The pulpit on the front of our zodiac Barbara Belle unfortunately broke earlier in the month, and it was a challenge for me to figure out how to tag without the pulpit. After a morning of trial and error, we figured it out and were able to tag more easily!
Tagging a whale in a cooperative bubble net feeding group without the usual bow pulpit. Video taken by Lauren Eckert.
In August, we focused on solitary whales foraging on krill, and it was often a challenge to find the whales. Cooperative bubble netting whales often stay in the same area for multiple days at a time, but solitary whales are often far away from each other and travel more frequently. It was also a different experience approaching a solitary whale versus a whale in a dense group, but luckily we found enough calm whales close enough to the field station to tag. Our best day of tagging was late in the month when we found many whales just 30 minutes north of the field station, and I was able to tag five of them. Looking at the photos and videos later, we realized that we tagged one of the same whales in June in a cooperative bubble netting group that we did in August feeding on krill! This whale, Fish Bones, was in the same August deployment switching between lunging on krill at 60 meters depth, and blowing a bubble net at 20 meters depth. These tag deployments on Fish Bones give us more evidence that whales can adapt their feeding behavior based on the prey species, density, depth, and time of year.
Video from a GoPro of a tag deployment on a solitary krill foraging whale
Acknowledgements
I am so grateful for the field team I got to work with this summer! Dana Bloch led our whale survey trips and kept everyone fed, organized, and laughing. Jess and Sarah were photographers extraordinaire, and Lewis, Liah, and Madi were drone professionals. I am also grateful for Andy’s patience, and Lauren’s enthusiasm.
Photo of the June field team on a hike looking over Warm Springs Bay (left to right: Jess McCoppin, Lewis Evans, Gussie Hollers, Dana Bloch, and Sarah Perryman)
We want to acknowledge the Tlingit land that we work on, and the significance of the humpback whale (sʼéetʼ) to the Tlingit people. We use minimally invasive techniques and undergo a rigorous permitting process in order to interact with whales. We are very grateful to be able to study them and contribute to their conservation and protection.
We also want to thank our partners, collaborators, and funders who make it possible for us to study these animals safely and responsibly. I am thankful for the guidance of Andy, Will, and Lars who started the tagging program at AWF and MMRP and who tagged 50+ whales in Alaska between 2019 and 2022! Their experience and data collection have been invaluable to me.
All research was conducted under NOAA/NMFS permit 19703 and IACUC approvals.
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