Humpback whale bioenergetics: Reflecting on a productive year of fieldwork in Hawaii and SE Alaska
Written by Martin van Aswegen
Following disrupted fieldwork in 2020, this year was a great opportunity for MMRP PhD student Martin van Aswegen and Director Dr. Lars Bejder to make up for lost time and data. Representing our third consecutive year of data collection on humpback whale (Megaptera novaeangliae) body condition across Hawaii and Alaska, 2021 was shaping up to be an important year for the project. The humpback whale energetics project aims to quantify the energetic costs associated with migration, reproduction, growth and foraging across their Hawaiian breeding and Southeast Alaskan foraging grounds. Multiple data streams are being collected, including morphometric measurements from unoccupied aerial systems (UAS; drones), lipid composition from biopsy sampling and fine-scale behavior recorded on suction-cup customized animal tracking systems (CATS) tags. A multi-faceted project like this spanning across large temporal and spatial scales would not be possible without the support of close collaborators, including Dr. Andy Szabo from the Alaska Whale Foundation (AWF), Jens Currie and Stephanie Stack from Pacific Whale Foundation (PWF), Dr. Adam Pack at the University of Hawaii at Hilo (UHH), Dr. Kristi West at the University of Hawaii Marine Mammal Stranding Lab (MMSL), Goldbogen Lab at Stanford University’s Hopkins Marine Station, and the Friedlaender Lab at University of California, Santa Cruz.
Primary objectives of the project include:
1. Quantifying intra- and inter-annual variation in humpback whale body condition on their Hawaiian breeding grounds;
2. Quantifying intra- and inter-annual variation in humpback whale body condition and mass acquisition rates on their Southeast Alaskan foraging grounds;
3. Model age- and sex-specific growth (body length and volume) and volume fluctuations in North Pacific humpback whales throughout their migratory cycle, and;
4. Using UAS, quantify scarring rates consistent with non-lethal entanglement and vessel collision across both Hawaii and Southeast Alaska.
This year, the aim was to collect morphometric measurements throughout the entire winter breeding season. This represented consistent field effort from the beginning of January to the end of March. In previous years, fieldwork on the breeding grounds of Maui was conducted in close collaboration with PWF and UHH during 10-day blocks in January and March. Such sampling windows represented ‘early’ and ‘late’ season phases, respectively. This year was no different with the team collecting multiple streams of data including photo identification images, unoccupied aerial system (UAS)-derived morphometric measurements, biopsy samples and behavioral observations. Having improved our field protocols over the preceding two years, the team proved to be a well-oiled machine across the two sampling stints, with biopsy-lead Dr. Adam Pack (UHH) collecting over 170 samples. These skin and blubber samples will be shared across multiple analyses exploring fluctuations in steroid hormones and adiposity. Where possible, biopsied whales were also measured using UAS providing important contextual information on the effect of body size and condition on fluctuating hormones and behavioral roles. In total, 250 UAS flights were conducted over the 10-day January and March stints, with 350 and 285 morphometric measurements collected, respectively.
Figure 1: A side-by-side comparison of the change in the body condition of SEAK-0206 aka ‘Zarpe’ between measurements in March 2019 and January 2021. Note the pronounced skull, rib bones, back bone and lice coverage in the right image.
In January, the team received a report from a local operator (thank you PacWhale Eco-Adventures) describing an adult whale in extremely poor condition off Maalaea Bay. It was a sad sight upon arrival – an adult humpback whale travelling very slowly on the surface, emaciated and heavily colonized by cyamids (whale lice). These creepy-looking hitchhikers (Cyamus boopis) are almost exclusively found on humpback whales, with large infestations indicative of unhealthy whales often moving slowly. Over the years we have had few opportunities to measure whales in such poor health, so we immediately launched the UAS and obtained morphometric measurements. With little strength left to fluke-up dive, we managed to obtain GoPro footage of its ventral fluke providing a valuable identification image. The whale was identified as SEAK-0206 aka ‘Zarpe’ – a mature female we last measured on her Southeast Alaskan feeding grounds in March 2019. The difference in her body volume between March 2019 and January 2021 said it all with a relative decrease of 48%, from 33m3 to 17m3 (Figure 1). Despite being 13.2 m in length, Zarpe exhibited a body volume equivalent to that of a yearling calf (<10 m). Given her condition, behavior and location, it is unlikely Zarpe would have made it back to her feeding grounds. Such an encounter demonstrated the value of quantifying differences in body condition using non-invasive UAS photogrammetry.
Figure 2: A map showing our study area off the leeward side of Maui, Hawaii. UAS measurement locations are colored by month (n=1487).
Between field efforts with PWF and UHH, the MMRP team continued boat-based data collection within the leeward waters of the Au’au Channel and Maalaea Bay (Figure 2) with the aim of collecting as many UAS-measurements as possible across all demographic groups. There was a key focus on obtaining repeat measurements of the same individuals over time to assess changes in body size. For example, repeated measurements of adult whales can provide estimates of the rate at which adults (including lactating females) lose body volume (BV) while fasting. The opposite is true for calves dependent on mother’s nutrient-rich milk, where marked changes in BV and total length (TL) should be occurring prior to northbound migration. Over 33 boat days, 528 UAS flights were conducted with 852 morphometric measurements collected, totaling 1487 measurements of approximately 1200 individual whales for the season. In total, 405 unique mother-calf pairs were measured. Within-season repeat measurements were collected on approximately 15 mother-calf pairs and 78 juvenile/adults. The longest period between first and last measurements of a mother-calf pair was 38 days. Over this period, the calf increasing in TL and BV by 20.8% and 138%, respectively, while the mother lost nearly 12% of her initial BV (Figure 3). Preliminary data on calf growth in Hawaii indicate mean daily increases in TL and BV of approximately 2.06cm (SE=0.5cm) and 0.04m3(SE=0.01m3), respectively.
Figure 3: UAS images comparing absolute changes in body condition exhibited by a mother (PWF-NP_5223) and her calf over 38 days on their Maui breeding grounds.
Overall, the 2021 breeding season was a resounding success, with nearly 1500 morphometric measurements, >170 biopsy samples and >630 photo identification images collected. Unfortunately, it was difficult to get fluke identification images for all whales, especially mothers who were fluking approximately 48% of the time (we were able to get fluke images for ~56% of adults).
While on the water, we were able to identify and measure several well-known whales from Southeast Alaska. We were ecstatic every time this happened as it really was a ‘needle in a haystack’ scenario and obtaining measurements of the same individuals on their breeding and foraging grounds is something we have been striving to achieve from day one. To date, over 75 whales have been measured in Hawaii and Alaska with less than a year between measurements. We thank Ted Cheeseman and Happywhale for their support in making this happen. Interestingly, of the 448 measured whales already in the Happy Whale system, only 54 individuals had existing Southeast Alaska identification codes, representing approximately 12% of identified whales. As the breeding season wrapped up, we could not help but wonder how many of those 54 whales we would see again ~2,900 miles north in Southeast Alaska later in the year?
Following a field season in 2020 due to COVID-19, we were eager to commence data collection efforts on one of the principal foraging grounds for North Pacific humpback whales - Southeast Alaska. This year represented the fourth consecutive year of data collection in close collaboration with Dr. Andy Szabo and AWF. In past years, humpback whale body condition data would be collected from the beginning of the foraging season (Spring) through to the end of September (early Fall), representing approximately five months of continuous sampling throughout the feeding season. Such extensive time on the foraging grounds provides valuable opportunities to quantify body condition across multiple demographic groups (i.e., calves, juveniles, adults, lactating females) throughout the foraging season with multiple years of effort allowing for inter-annual comparisons in body condition and mass acquisition rates.
Figure 4. Ahhhhh morning coffees with a view. The beautiful scenery as seen from the Alaska Whale Foundation Field Station on a crisp, Spring morning.
This year, the team mobilized in late April and arrived in Warm Springs Bay where we were greeted with glorious snow-capped mountains and a refreshing chill in the air (Figure 4). There was a late dumping of snow on Baranof Island in the weeks prior to our arrival so this Spring felt different compared to warm and dry Spring arrivals in years past. We were pleasantly surprised to find brown bear paw prints in the snow adjacent to freshly-gnawed skunk cabbage – it was just a matter of time before the rest of the bears would awake from hibernation and migrate to lower elevations with food on their mind.
Speaking of migrating with food in mind, we were expecting humpback whales to start returning from the breeding grounds, slowly filtering back into Southeast Alaska’s Inside Passage between April and June. One of the neat aspects of the Southeast Alaska population is the high site fidelity exhibited by individuals, providing unique opportunities to not only find the same whales throughout the foraging season but also having somewhat-consistent access to the same individuals across years. With this in mind, we were keen to measure whales as early into the foraging season as possible, with the hopes of repeatedly quantifying changes in their body condition and body volume over the subsequent five months.
Figure 5: A map showing Southeast Alaska’s Inside Passage with locations of UAS measurements of humpback whales colored by month (n=731).
This year turned out to be a bumper year for morphometric measurements in Southeast Alaska. Between May and October 315 UAS flights were flown, capturing 731 measurements on 508 individuals. To put this in perspective, our previous best year was 2019 when 415 measurements were collected over a slightly larger number of field days and UAS flights (54 days/335 flights in 2019 vs 49 days/315 flights in 2021). Our study area covered the majority of Southeast Alaska’s Inside Passage, including Chatham Strait, Frederick Sound, Icy Strait, Stephens Passage and Seymour Canal (Figure 5). Of the 508 unique individuals sampled, 392 matched to existing whales in Happywhale, with 130 of those measured in previous years.
An exciting part of this year was the expanded survey effort as part of AWF’s comprehensive monitoring program. This program consisted of monthly systematic surveys throughout the Inside Passage focusing on population abundance, distribution and health questions. Importantly, University of Alaska Fairbanks Masters Student Dana Bloch has commenced an exciting oceanographic program utilizing water sampling and high-resolution conductivity, temperature and depth (CTD) readings. These valuable data will inform multiple existing programs quantifying inter- and intra-annual variation in whale abundance, distribution, health and diet.
Of the 54 Southeast Alaska whales identified in Maui between January and April, 24 (44%) were resighted and re-measured on their foraging grounds. While most of these individuals were mature adults, three mothers were also resighted however one appeared to be without her calf on the foraging grounds. The remaining two mother-calf pairs were re-measured 139 and 171 days after they were measured off Maui, respectively. The latter pair consisted of SEAK-1789 aka ‘ZeroTime’ and her calf measured in mid-February and early August (Figure 6). ZeroTime appeared to be in relatively good body condition, with a BV decrease of at least 4.3m3 or ~12%. This is impressive considering the size of her calf who increased by 47% and 236% in TL and BV, respectively, over the same 171 days.
Figure 6: Images comparing absolute changes in body condition and size of mother SEAK-1789 aka ‘Zerotime’ and her calf in Hawaii (top) and Southeast Alaska (bottom) between February and August 2021 (171 days).
Such a successful year would not have been possible without the support of our project collaborators. We would like to thank the Alaska Whale Foundation, Pacific Whale Foundation, University of Hawaii at Hilo, Dr. Kristi West at MMSL, Goldbogen Lab at Stanford University’s Hopkins Marine Station, and the Friedlaender Lab at University of California, Santa Cruz.
We would also like to thank the many people who assisted along the way, including but not limited to:
Hawaii: Jens Currie, Stephanie Stack, Abigail Machernis, Grace Olsen, Florence Sullivan, Dr. Adam Pack, Dr. Kristi West, Jessie Hoffman, Brijonnay Madrigal, Liah McPherson, Kirby Parnell, Chloe Kotik, Lewis Evans, Joe Giglio, Hannah von Hammerstein, Javier Garcia, Chris Ferrante, Dan Kraver, PacWhale Eco Adventures, Omidyar Ohana, Hallie Walker, Chrissy Lovitt, Emma Nelson, Laule’a Blanco, Lee James and the Hawaiian Islands Humpback Whale National Marine Sanctuary.
Southeast Alaska: Dr. Andy Szabo, Dana Bloch, Ada Harrison, Rhianna Thurber, Alyssa Wile, Makayla Guinn, Alex Jenkins, Sonja Feinberg, Annie Bartlett, Hunter Warick, Will Gough and the Warm Springs Bay community.
Well, that is a wrap for 2021. What an epic year full of laughs, adventures and a diverse range of humpback whale shenanigans. We now have a couple of months to analyze data and prepare before humpback whales begin to arrive again. Some overzealous juveniles have already been sighted off Maui!
Until next time.
If you would like to hear more about the project, we will be presenting our program and findings at the virtual Hawaiian Islands Humpback Whale National Marine Sanctuary Research Symposium on November 4 and 5 (9am – 11am HST; register for free at https://register.gotowebinar.com/register/3737916640499178768).
All research activities were conducted in accordance with NOAA permits 21476, 21321, 14585, 19655 and 19703. UAS activities were conducted in compliance with FAA Part 107 regulations.