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

Abstract

Summary 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.

Effects of variation in the abundance and distribution of prey on the foraging success of central place foragers

“…Acoustic survey data revealed contrasting foraging conditions in terms of the regional abundance, depth distribution and spatial configuration of anchoveta in early December 2008 and 2009 (Boyd et al . ,b; Fig. ).…”

“…One hundred Bayesian posterior predictions of the abundance and depth distribution of anchoveta in each grid cell were generated based on acoustic survey data for 2008 and 2009 (Boyd et al . ,b). Eight sets of 100 simulated prey fields were then constructed from the Bayesian posterior predictions, representing the eight possible combinations of high or low regional abundance with shallow or deep depth distributions and broad or concentrated spatial configurations (see Appendix S2 for further details.…”

“…For both species, Boyd et al . () estimated the probability of patch selection, , in each cell ( i ) from the observed probability than an individual made at least one dive in a cell as a function of the relative abundance of prey in the upper water column. Following this analysis, the probability of patch selection was parameterized for Peruvian Boobies in the IBFM as follows:and for Guanay Cormorants as follows:where ρ i refers to anchoveta densities and d i to the upper depth limit of anchoveta aggregations.…”

Tracking Cairns: Biologging Improves the Use of Seabirds as Sentinels of the Sea

“…Individuals dove more often when prey were located at shallow depth, but not necessarily when the relative abundance of prey was higher Boyd et al, 2015 parameters. A major advantage of biologging is the potential to estimate food supply over multiple spatial and temporal scales.…”

“…The consensus from the studies in Table 1 is that biologgers are useful tools that demonstrate how seabirds adjust their foraging behavior to fish stocks and distribution, sometimes showing strong correlations (Litzow and Piatt, 2003;Bertrand et al, 2012;Cohen et al, 2014;Boyd et al, 2015). Three studies found a linear correlation between fish stocks and foraging parameters (Litzow and Piatt, 2003;Bertrand et al, 2012;Cohen et al, 2014), which suggests that foraging distance from the colony, diving depth, and diving activity may be good candidate parameters for detection of changes in food supply.…”