Group hunting behaviour in striped marlin, Kajikia audax

• Applicant: Matthew Hansen, Ph.D.
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Sensory and Behavioural Biology
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 455800376

Group hunting has been a key topic in the field of behavioural ecology for decades and concentrates on the evolutionary advantages of sociality and cooperation. In this research proposal we address two fundamental aspects of group hunting behaviour which need further investigation: i) how do individual predators interact in time and space with each other and with their prey to maximise their capture efficiency, and (ii) how do physical constraints determine and explain variation in hunting strategies used by predators. Descriptions of group hunts in the literature have traditionally been very qualitative. However, nowadays the temporal and spatial resolutions of animal movement data collected in the wild are as high as those achieved in many laboratory settings. Thus, recent advantages in remote sensing technology allow for the application of collective behaviour methodology to wild predation events. Bringing collective behaviour methodology into the field not only allows researchers to answer existing ecological and evolutionary questions with greater realism, it advances the field by allowing new questions on systems previously untestable in the laboratory to be addressed. Our project will use state-of-the-art methodology to quantify the predator-prey dynamics of a unique study system; groups of striped marlin (Kajikia audax) hunting schools of sardine, Sardinops sagax, and mackerel, Scomber japonicus off the coast of Baja California, Mexico. Because it is an open ocean system, we can investigate (A) functions, (B) mechanisms, and (C) morphological characteristics that are not commonly addressed in the literature which is traditionally focused on terrestrial systems. Predator-prey relationships in the open ocean are characterised by large relative size differences between predator and prey, a lack of environmental structure for animals to hide and predators often use body parts to strike multiple prey at once. The objectives we propose and the advances we aim to make for group hunting research are only possible as our study system is uniquely tractable across different stages of the hunt and at multiple spatial scales. Our main objectives are:A.) Functions: Measure how attack rate and capture rate of individually identified predators are affected by predator and prey group size.B.) Mechanisms: Identify the attack patterns for different stages of the hunt, i.e. the chase and when prey are surrounded. C.) Morphology: Investigate how morphological traits (notably characteristics of the bill) affect individual and group behaviour of marlin.Understanding how interactions between multiple predators and their schooling prey affect attack dynamics and capture efficiencies and therefore the potential benefits of cooperating with conspecifics will greatly advance our understanding of the evolution of group hunting and animal sociality.

• DFG Programme: Research Grants