Dear MARMAM colleagues, We are pleased to announce that the following paper is now available online: Enrico Pirotta and KC Bierlich, Leslie New, Lisa Hildebrand, Clara N. Bird, Alejandro Fernandez Ajó, Leigh G. Torres. Modeling individual growth reveals decreasing gray whale body length and correlations with ocean climate indices at multiple scales. Global Change Biology. Abstract: 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, behaviour 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 association with climate change and other anthropogenic stressors. Our modelling approach is broadly applicable across multiple systems where morphological data on megafauna are collected using drones. Keywords: baleen whales, Bayesian modelling, drones, morphology, Pacific Decadal Oscillation, photogrammetry, shrinking size, upwelling and relaxation. A PDF copy of the paper can be downloaded for free from:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/gcb.17366 Please do not hesitate to contact us for any question regarding our work. Best Regards, Enrico Pirotta and KC Bierlich
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