Multi-Predator Aggregations in the Open Ocean

• Applicant: Matthew Hansen, Ph.D.
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Sensory and Behavioural Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546442463

The most spectacular predator aggregations on the planet occur in the open ocean, but our understanding of how and why different predator species aggregate is heavily influenced by terrestrial research. Terrestrial predators tend to aggregate at carcasses, where differences in predator phenotype and inter-specific dominance hierarchies determine the rules of prey access. However, because of differences in the physical environment and dominant prey type, the mechanisms determining the nature of between predator interactions in terrestrial systems is unlikely to directly translate to conditions in the open ocean. Each year, off the coast of Baja California in the Pacific Ocean, a plethora of predators, numerically dominated by striped marlin (but including a diverse range of Teleosts, cetaceans, pinnipeds and birds) attack large schools of prey fish. Studies of comparable open ocean multi-predator aggregations around the world have traditionally been rather qualitative and have primarily focused on recording the co-occurrence of certain predator species. Thus, the field still lacks the quantitative data (spatio-temporal positions of predators and prey, attack and capture rates) that are required to understand the mechanisms and functions of predator interactions which form part of these ecologically important events. On the back of the conceptual and methodological advancements made under DFG project that allowed our team to collect the first high-resolution trajectories of predator-prey interactions in the open ocean, this multi-disciplinary project will specifically provide this missing data. In combination with computer simulations, we will investigate the behavioral ecology of open ocean multi-predator aggregations at unprecedented levels of detail. The project has 3 main objectives to investigate regarding the formation and maintenance of multi-predator aggregations: (A) Mechanisms and Opportunities - how does the prey type promote the existence of multi-species aggregations, are some predators (e.g. striped marlin) integral to these aggregations, if so, how? (B) Function and Interaction Type - what is the nature of the interactions between striped marlin and the other predator species (competitive, commensal, mutualistic). (C) Integrating Behavior and Morphology - how do the different predator phenotypes relate to variations in attack behavior and the generation of foraging opportunities for hetero-specific competitors? Fulfilling these objectives will provide important insights into the role of between-predator interactions in the ecology of the open ocean.

• DFG Programme: Research Grants