Effects of variation in the abundance and distribution of prey on the foraging success of central place foragers
Résumé
1. Seabirds and pinnipeds are vulnerable to reductions in prey availability, especially during
the breeding season when spatial constraints limit their adaptive capacity. There are growing
concerns about the effects of fisheries on prey availability in regions where large commercial
fisheries target forage fish.
2. For breeding seabirds and pinnipeds, prey availability depends on a combination of abundance,
accessibility, patchiness and distance from the colony. An understanding of the aspects of prey availability
that determine foraging success is essential for the design of effective management responses.
3. We used a mechanistic individual-based foraging model based on observed data for two seabird
species, the Peruvian Booby Sula variegata and Guanay Cormorant Phalacrocorax
bougainvilliorum, to simulate the foraging patterns of seabirds feeding on schooling fish. We ran
the model over simulated prey fields representing eight possible combinations of high or low
prey abundance, shallow or deep prey, and broadly distributed or spatially concentrated prey.
4. The results highlight the importance of the accessibility of prey. Depth distribution was
the primary factor determining modelled foraging success for both species, followed by abundance,
and then spatial configuration.
5. Synthesis and applications. The individual-based foraging model provides a spatially explicit
framework for assessing the effects of fisheries on the foraging success of seabirds and
other central place foragers, and for evaluating the potential effectiveness of marine-protected
areas and other fisheries management strategies for safeguarding central place foragers in
dynamic ecosystems. Our analysis indicates that broad-scale fisheries management strategies
that maintain forage fish above critical biomass levels are essential, but may need to be supplemented
by targeted actions, such as time–area closures, when environmental conditions
lead to low prey abundance or reduce prey accessibility for seabirds or pinnipeds of conservation
concern. The individual-based foraging model is adaptable and could be reconfigured for
application to other species and systems.