title: Inferring cetacean population densities from the absolute dynamic topography of the ocean in a hierarchical Bayesian framework.
abstract: 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.
authors.affiliation: Posgrado en Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Distrito Federal, 04510, Mexico; Unidad La Paz, Centro de Investigación Científica y de Educación Superior de Ensenada, La Paz, Baja California Sur, 23050, Mexico.
authors.forename: Mario A
authors.initials: MA
authors.lastname: Pardo
authors.affiliation: Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla, California, 92037-1508, United States of America.
authors.forename: Tim
authors.initials: T
authors.lastname: Gerrodette
authors.affiliation: Unidad La Paz, Centro de Investigación Científica y de Educación Superior de Ensenada, La Paz, Baja California Sur, 23050, Mexico.
authors.forename: Emilio
authors.initials: E
authors.lastname: Beier
authors.affiliation: Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, La Paz, Baja California Sur, 23096, Mexico.
authors.forename: Diane
authors.initials: D
authors.lastname: Gendron
authors.affiliation: Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla, California, 92037-1508, United States of America.
authors.forename: Karin A
authors.initials: KA
authors.lastname: Forney
authors.affiliation: Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla, California, 92037-1508, United States of America.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Chivers
authors.affiliation: Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla, California, 92037-1508, United States of America.
authors.forename: Jay
authors.initials: J
authors.lastname: Barlow
authors.affiliation: Marine Mammal Institute, Oregon State University, Newport, Oregon, 97365, United States of America.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Palacios
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D002591:Cetacea; D015233:Models, Statistical; D009792:Oceans and Seas; D011156:Population Density; D062206:Spatial Analysis