Size

Size matters, especially for whales because they are a “capital breeder”, as opposed to the other group of mammals that are “income breeders”.

Being a capital breeder means that the whale feasts during one part of the year to gain and store all the energy it needs to support (“finance”) its energetic requirements for the whole year. For a gray whale, this means eating a lot during its foraging season (~May through November), storing the fat it gained as blubber, and then using up that blubber energy store throughout the whole year as it forages, migrates thousands of miles, breeds and socializes, avoids predation, grows (if it is a sub-adult), and supports pregnancy and lactation (if it is a reproductive female). That’s a lot of energy to store, and the bigger the whale is, the more energy it can store – so size matters!
Turns out Oregon gray whales are smaller and skinnier than gray whales that feed in the Arctic. The drone data we collected during hundreds of flights over gray whales in Oregon during the past nine years allowed us to determine that these PCFG gray whales in Oregon waters have shorter total lengths, smaller head sizes, and smaller fluke spans than the larger Eastern North Pacific gray whale population (~15,000 individuals) that feed in the Arctic.
comparison chart of pacific and eastern groups of gray whales

What’s even more dramatic is that these gray whales foraging in the northeast Pacific have gotten 13% shorter in the last few decades! We flew drones over the same individual gray whales for eight years, which allowed us to measure their length and determine their growth rates, finding that a whale born in 2020 would end up being about 1.65 meters (5 feet, 5 inches) shorter than a gray whale born prior to 2000. That’s a huge difference!

gray whale as seen from drone
Our work also found that this decline in gray whale length is correlated with changes in ocean conditions (specifically, the ratio of upwelling and relaxation each year), which indicates that the body size of gray whales responds to changing environmental conditions that controls their food availability. But we have also learned that the unique feeding tactics used by these gray whales in the shallow waters of coastal Oregon are related to their size. So, maybe their changing lengths are a positive adaptation to help them feed better. We still have so much to learn!

Want to read more? Check out these resources:

Bierlich KC, Kane A, Hildebrand L, Bird CN, Fernandez Ajo A, Stewart JD, Hewitt J, Hildebrand I, Sumich J, Torres LG (2023) Downsized: gray whales using an alternative foraging ground have smaller morphology. Biol Letters 19:20230043 doi:10.1098/rsbl.2023.0043. https://royalsocietypublishing.org/doi/abs/10.1098/rsbl.2023.0043

Pirotta E, Bierlich K, New L, Hildebrand L, Bird CN, Fernandez Ajó A, Torres LG (2024) Modeling individual growth reveals decreasing gray whale body length and correlations with ocean climate indices at multiple scales. Global Change Biology 30:e17366 https://onlinelibrary.wiley.com/doi/10.1111/gcb.17366

Torres, L.G., C.N. Bird, F. Rodríguez-González, F. Christiansen, L. Bejder, L. Lemos, J. Urban R, S. Swartz, A. Willoughby, J. Hewitt, and K. Bierlich, Range-Wide Comparison of Gray Whale Body Condition Reveals Contrasting Sub-Population Health Characteristics and Vulnerability to Environmental Change. Frontiers in Marine Science, 2022. 9. https://www.frontiersin.org/article/10.3389/fmars.2022.867258

Press releases:

https://news.oregonstate.edu/news/gray-whales-feeding-along-pacific-northwest-coast-are-smaller-their-counterparts-who-travel

https://news.oregonstate.edu/news/pacific-coast-gray-whales-have-gotten-13-shorter-past-20-30-years-oregon-state-study-finds

Blog: A smaller sized gray whale: recent publication finds PCFG whales are smaller than ENP whales https://blogs.oregonstate.edu/gemmlab/2023/11/06/a-smaller-sized-gray-whale-recent-publication-finds-pcfg-whales-are-smaller-than-enp-whales/