Seabirds mediate intraguild and competitive interactions in a shark community

Abstract Intraguild predation (IGP) and competition significantly influence resource utilization patterns among sympatric species. The presence of alternative prey (consumed only by intraguild [IG] predators and not IG prey) may promote coexistence and have a profound effect on distribution patterns. Models predict that IG predator distributions should match alternative prey distribution when alternative prey are abundant. IG prey should risk‐match by selecting safe habitats. When alternative prey are scarce, coexistence may be facilitated by a more even distribution across habitats or other mechanisms. Based on the models, the distribution of IG prey may be indirectly mediated by the alternative prey. French Frigate Shoals atoll, Hawaii, has a predator community that includes IG predators (tiger sharks), IG prey (gray reef sharks), and competitors (gray reef and Galapagos sharks, tiger and Galapagos sharks). Tiger sharks will consume alternative prey (fledgling seabirds) which occur in high abundance in the summer. We used acoustic telemetry of 128 sharks to test predictions of habitat use. As predicted by the model, tiger sharks showed a strong selection for islets where albatross fledge during the summer, whereas gray reef sharks avoided these areas and used other habitats. During the winter, tiger sharks showed a broader use of habitats and gray reef sharks showed a greater use of islets in lagoons. Galapagos sharks showed greater overlap with tiger sharks, but also avoided the summer islets where birds were fledging. Seabirds partially mediate habitat use by a shark community through their influence on a likely keystone species: tiger sharks. Our study highlights the importance of alternative prey and asymmetrical IGP in driving space‐use patterns of marine predators.