Dear MARMAM subscribers,
My coauthors and I are pleased to share with you the recent
publication of the article:
Pardo MA, Gerrodette T, Beier E, Gendron D, Forney KA, Chivers JS,
Barlow J, Palacios DM (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
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.
The full article is freely available at:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120727
Kind regards,