Inferring Cetacean Population Densities from the Absolute Dynamic Topography of the Ocean in a Hierarchical Bayesian Framework

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  • We inferred the population densities of blue whales (Balaenoptera musculus) and short-beaked common dolphins (Delphinus delphis) in the Northeast Pacific Ocean as functions of the water-column’s physical structure by implementing hierarchical models in a Bayesian framework. This approach allowed us to propagate the uncertainty of the field observations into the inference of species-habitat relationships and to generate spatially explicit population density predictions with reduced effects of sampling heterogeneity. Our hypothesis was that the large-scale spatial distributions of these two cetacean species respond primarily to ecological processes resulting from shoaling and outcropping of the pycnocline in regions of wind-forced upwelling and eddy-like circulation. Physically, these processes affect the thermodynamic balance of the water column, decreasing its volume and thus the height of the absolute dynamic topography (ADT). Biologically, they lead to elevated primary productivity and persistent aggregation of low-trophic-level prey. Unlike other remotely sensed variables, ADT provides information about the structure of the entire water column and it is also routinely measured at high spatial-temporal resolution by satellite altimeters with uniform global coverage. Our models provide spatially explicit population density predictions for both species, even in areas where the pycnocline shoals but does not outcrop (e.g. the Costa Rica Dome and the North Equatorial Countercurrent thermocline ridge). Interannual variations in distribution during El Niño anomalies suggest that the population density of both species decreases dramatically in the Equatorial Cold Tongue and the Costa Rica Dome, and that their distributions retract to particular areas that remain productive, such as the more oceanic waters in the central California Current System, the northern Gulf of California, the North Equatorial Countercurrent thermocline ridge, and the more southern portion of the Humboldt Current System. We posit that such reductions in available foraging habitats during climatic disturbances could incur high energetic costs on these populations, ultimately affecting individual fitness and survival.
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  • Pardo, M. A., Gerrodette, T., Beier, E., Gendron, D., Forney, K. A., Chivers, S. J., ... & Palacios, D. M. (2015). Inferring Cetacean Population Densities from the Absolute Dynamic Topography of the Ocean in a Hierarchical Bayesian Framework. PLoS ONE, 10(3), e0120727. doi:10.1371/journal.pone.0120727
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  • 10
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  • The survey cruises for cetacean data collection were funded by the U.S. National Marine Fisheries Service as part of its annual budget. This study received funds from Consejo Nacional de Ciencia y Tecnología (CONACyT;, through the project “Un estudio de la corriente costera Mexicana y el Pacífico adyacente, con SeaGlider, cruceros oceanográficos y datos de satélite” (Grant No. 168034-T-1753; PI: EB), a Ph.D. scholarship and an international internship grant to MAP. The authors also received financial support from Posgrado en Ciencias del Mar y Limnología ( at Universidad Nacional Autónoma de México, and Laboratorio de Ecología de Cetáceos y Quelónios at Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional (, through the project “Estructura poblacional y movimiento de algunos cetáceos del Golfo de California” (Grant No. SIP-20070803; PI: DG). MAP received grants from Cetacean Society International (, The Ocean Foundation (, American Cetacean Society (, Sociedad Mexicana de Mastozoología Marina (SOMEMMA;, and Consejo Sudcaliforniano de Ciencia y Tecnología (COSCyT; DMP was funded by the Interagency NASA Climate and Biological Response Program (Grant No. NNX11AP71G; PI: H. Bailey).
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