|Photo credit DivingSeaSafari|
They tested the effect of dynamic environmental covariates from a coupled biophysical oceanographic model on patch choice in diving leatherback turtles, and compared the effects of parameters measured at the surface and at depth. The covariates included distance to future patch, temperature, salinity, meridional current velocity (current in the north–south direction), zonal current velocity (current in the east–west direction), phytoplankton density, diatom density, micro-plankton density, and meso-zooplankton density.
They found significant correlation between movement and the parameters for oceanic covariates in eight of the tracks. Of particular note, for one turtle they observed a lack of correlation between movements and a modeled index of zooplankton at the surface, but a significant correlation between movements and zooplankton at depth. Two of the turtles express a preference for patches at depth with elevated diatoms, and two turtles prefer patches with higher mezozooplankton values at depth. In contrast, four turtles expressed a preference for elevated zooplankton patches at the surface, but not at depth.
The authors suggest that our understanding of a marine predator’s response to the environment may change significantly depending upon the analytical frame of reference, that is whether relationships are examined at the surface, at depth, or at different temporal resolutions. They also tested the effects of accounting for ocean currents on the movement patterns and found that for 13 of the 15 turtles, the parameter governing distance to the next patch decreased.
Schick RS, Roberts J, Eckert S, Clark J, Bailey H, Chai F, Shi L & Halpin P 2013 . Pelagic movements of pacific leatherback turtles (Dermochelys coriacea) reveal the complex role of prey and ocean currents. BMC Movement Ecology 1(11).