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

Abstract

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. We used a mechanistic individual-based foraging model (IBFM) based on observed data for two seabird species, the Peruvian Booby Sula variegata and Guanay CormorantPhalacrocorax 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 (IBFM) provides a spatially-explicit framework for assessing the effects of fisheries on the foraging success of seabirds and other central place foragers (CPFs), and for evaluating the potential effectiveness of marine protected areas and other fisheries management strategies for Accepted ArticleThis article is protected by copyright. All rights reserved.safeguarding CPFs 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 IBFM is adaptable and could be reconfigured for application to other species and systems.

Targeted prey fields determine foraging effort thresholds of a marine diver: Important cues for the sustainable management of fisheries

“…Non‐random foraging site selection and foraging area fidelity are well documented for seabirds (e.g. Cairns & Schneider, ; Gorke & Brandl, ), including penguins (Baylis et al, ), and the foraging locations of diving seabird species are known to be correlated with favourable depth distributions of their prey (Boyd et al, , ; Zamon et al, ). Foraging site selection by African penguins in Algoa Bay, especially for penguins breeding on Bird Island, may be related to the dynamic nature of oceanographic processes in this region (van Eeden, Reid, Ryan, & Pichegru, ; Goschen, Schumann, Bernard, Bailey, & Deyzel, ) and the influence that these processes have on the three‐dimensional distribution of small pelagic fish around Bird and St Croix islands (McInnes et al, ).…”

Taking movement data to new depths: Inferring prey availability and patch profitability from seabird foraging behavior

“…The depth distribution of prey plays an important role in how predators use their habitat (Benoit‐Bird et al., ; Boyd et al., ; Carroll et al., ). By exploring the relationship between the number of PCE with dive depth and duration, we have shown that two species, guillemots and razorbills, clearly made different decisions while exploiting the water column.…”

“…In other diving marine predators (e.g., the little penguin (Eudyptula minor), Peruvian booby (Sula variegata), and Guanay cormorant (Phalacrocorax bougainvilliorum)), the distribution of prey capture events and dives in the water column match the local distribution of their prey (Boyd et al, 2016;Carroll et al, 2017). Therefore, we assumed that the number of PCE performed in each dive is a measure of foraging effort occurring in the presence of prey.…”

“…However, it is not currently well known how the foraging patterns of these marine predators are influenced by the density, distribution, and behavior of prey and how they adjust their behavior in response to changes in prey availability. Modeled foraging behavior for Peruvian booby ( Sula variegata ) and Guanay cormorant ( Phalacrocorax bougainvilliorum ) suggest that depth distribution is the primary factor for foraging success followed by abundance and then spatial configuration of prey (Boyd et al., ).…”

Positive Interactions among Foraging Seabirds, Marine Mammals and Fishes and Implications for Their Conservation

“…Associations of aerial seabirds and diving species, whether birds, fish or mammals, are conspicuous worldwide and likely to include important positive interspecific associations (Evans, 1982;Au and Pitman, 1986;Camphuysen and Webb, 1999;Clua and Grosvalet, 2001;Davoren et al, 2010;Goyert et al, 2014;Boyd et al, 2016). The example of diving predators pushing bait balls of fodder fish to the surface is the most familiar of interspecific associations of seabirds in the open ocean (Cafaro et al, 2016).…”