Data from: Predictive modelling of habitat selection by marine predators with respect to the abundance and depth distribution of pelagic prey

1. Understanding the ecological processes that underpin species
distribution patterns is a fundamental goal in spatial ecology. However,
developing predictive models of habitat use is challenging for species
that forage in marine environments, as both predators and prey are often
highly mobile and difficult to monitor. Consequently, few studies have
developed resource selection functions for marine predators based directly
on the abundance and distribution of their prey. 2. We analysed
contemporaneous data on the diving locations of two seabird species, the
shallow-diving Peruvian Booby (Sula variegata) and deeper diving Guanay
Cormorant (Phalacrocorax bougainvilliorum), and the abundance and depth
distribution of their main prey, Peruvian anchoveta (Engraulis ringens).
Based on this unique data set, we developed resource selection functions
to test the hypothesis that the probability of seabird diving behaviour at
a given location is a function of the relative abundance of prey in the
upper water column. 3. For both species, we show that the probability of
diving behaviour is mostly explained by the distribution of prey at
shallow depths. While the probability of diving behaviour increases
sharply with prey abundance at relatively low levels of abundance, support
for including abundance in addition to the depth distribution of prey is
weak, suggesting that prey abundance was not a major factor determining
the location of diving behaviour during the study period. 4. The study
thus highlights the importance of the depth distribution of prey for two
species of seabird with different diving capabilities. The results
complement previous research that points towards the importance of
oceanographic processes that enhance the accessibility of prey to
seabirds. The implications are that locations where prey is predictably
found at accessible depths may be more important for surface foragers,
such as seabirds, than locations where prey is predictably abundant. 5.
Analysis of the relative importance of abundance and accessibility is
essential for the design and evaluation of effective management responses
to reduced prey availability for seabirds and other top predators in
marine systems.