Shaped by their environment: variation in blue whale morphology across three productive coastal ecosystems

Shaped by their environment: variation in blue whale morphology across three productive coastal ecosystems

Dawn R. Barlow¹*, K.C. Bierlich¹, William K. Oestreich², Gustavo Chiang³, John W. Durban⁴, Jeremy A. Goldbogen⁵, David W. Johnston⁶, Matthew S. Leslie⁷, Michael Moore⁸, John P. Ryan², Leigh G. Torres¹

¹Geospatial Ecology of Marine Megafauna Lab, Marine Mammal Institute, Department of Fisheries, Wildlife, and Conservation Sciences, Oregon State University, Newport, Oregon USA

²Monterey Bay Aquarium Research Institute, Moss Landing, California, USA

³Centro de Investigación para la Sustentabilidad (CIS) & Departamento de Ecología y Biodiversidad, Universidad Andrés Bello, Santiago, Chile

⁴Marine Mammal Institute, Oregon State University, Newport, Oregon, USA

⁵Hopkins Marine Station, Department of Biology, Stanford University, Pacific Grove, California, USA

⁶Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University Marine Laboratory, Beaufort, North Carolina, USA

⁷ National Climate Adaptation Science Center, United States Geological Survey, Reston, Virginia, USA

⁸Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA

*dawn.barlow@oregonstate.edu

Abstract: Species ecology and life history patterns are often reflected in animal morphology. Blue whales are globally distributed, with distinct populations that feed in different productive coastal regions worldwide. Thus, they provide an opportunity to investigate how regional ecosystem characteristics may drive morphological differences within a species. Here, we compare physical and biological oceanography of three different blue whale foraging grounds: (1) Monterey Bay, California, USA, (2) the South Taranaki Bight (STB), New Zealand, and (3) the Corcovado Gulf, Chile. Additionally, we compare the morphology of blue whales from these regions using unoccupied aircraft imagery. Monterey Bay and the Corcovado Gulf are seasonally productive and support the migratory life history strategy of the Eastern North Pacific (ENP) and Chilean blue whale populations, respectively. In contrast, the New Zealand blue whale population remains in the less productive STB year-round. All three populations were indistinguishable in total body length. However, New Zealand blue whales were in significantly higher body condition despite lower regional productivity, potentially attributable to their non-migratory strategy that facilitates lower risk of spatiotemporal misalignment with more consistently available foraging opportunities. Alternatively, the migratory strategy of the ENP and Chilean populations may be successful when their presence on the foraging grounds temporally aligns with abundant prey availability. We document differences in skull and fluke morphology between populations, which may relate to different feeding behaviors adapted to region-specific prey and habitat characteristics. These morphological features may represent a trade-off between maneuverability for prey capture and efficient long-distance migration. As oceanographic patterns shift relative to long-term means under climate change, these blue whale populations may show different vulnerabilities due to differences in migratory phenology and feeding behavior between regions.