Modeling individual growth reveals decreasing gray whale body length and correlations with ocean climate indices at multiple scales

Funding: This work was supported by the Office of Naval Research Marine Mammals and Biology Program (grant number: N00014-20-1-2760); the NOAA National Marine Fisheries Service Office of Science and Technology Ocean Acoustics Program (2016 and 2017) (grant number: 50-27); the Oregon State University...

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Bibliographic Details
Published in:Global Change Biology
Main Authors: Pirotta, Enrico, Bierlich, KC, New, Leslie, Hildebrand, Lisa, Bird, Clara, Fernandez Ajó, Alejandro, Torres, Leigh
Other Authors: University of St Andrews.School of Biology, University of St Andrews.Centre for Research into Ecological & Environmental Modelling
Format: Article in Journal/Newspaper
Language:English
Published: 2024
Subjects:
Baleen whales
Bayesian modeling
Drones
Morphology
Pacific Decadal Oscillation
Photogrammetry
Shrinking size
Upwelling and relaxation
DAS
Pacific
baleen whales
Online Access:https://hdl.handle.net/10023/30285
https://doi.org/10.1111/gcb.17366
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Summary:Funding: This work was supported by the Office of Naval Research Marine Mammals and Biology Program (grant number: N00014-20-1-2760); the NOAA National Marine Fisheries Service Office of Science and Technology Ocean Acoustics Program (2016 and 2017) (grant number: 50-27); the Oregon State University Marine Mammal Institute; and Oregon Sea Grant Program Development funds (2018) (grant number: RECO- 40-PD). Changes in body size have been documented across taxa in response to human activities and climate change. Body size influences many aspects of an individual's physiology, behavior, and ecology, ultimately affecting life history performance and resilience to stressors. In this study, we developed an analytical approach to model individual growth patterns using aerial imagery collected via drones, which can be used to investigate shifts in body size in a population and the associated drivers. We applied the method to a large morphological dataset of gray whales (Eschrichtius robustus) using a distinct foraging ground along the NE Pacific coast, and found that the asymptotic length of these whales has declined since around the year 2000 at an average rate of 0.05–0.12 m/y. The decline has been stronger in females, which are estimated to be now comparable in size to males, minimizing sexual dimorphism. We show that the decline in asymptotic length is correlated with two oceanographic metrics acting as proxies of habitat quality at different scales: the mean Pacific Decadal Oscillation index, and the mean ratio between upwelling intensity in a season and the number of relaxation events. These results suggest that the decline in gray whale body size may represent a plastic response to changing environmental conditions. Decreasing body size could have cascading effects on the population's demography, ability to adjust to environmental changes, and ecological influence on the structure of their community. This finding adds to the mounting evidence that body size is shrinking in several marine populations in ...

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