Blue acaras use pure pursuit rather than parallel navigation when pursuing robotic prey

Predators depend on their ability to accurately target and capture prey; however, identifying how predators capture highly evasive prey remains challenging. Experiments involving real predators and responsive robotic prey are a promising method to understand how predators can overcome prey escape tactics, since they allow prey behaviour to be controlled and experimentally manipulated. Using interactive robot-controlled prey, we tested how the predictability of the prey’s initial escape direction influenced the pursuit strategy adopted by blue acaras, Andinoacara pulcher. Individual fish were repeatedly presented with a single robot-controlled prey that was programmed to flee from the approaching predator. Predators experienced either predictable prey that consistently escaped in the same initial direction over successive trials or unpredictable prey that escaped in random directions, mimicking the variability that is commonly seen in the escape paths of real prey. To determine the predators' pursuit strategy, we analysed the trajectory of the predator during the period after the prey had started to escape. We compared the observed pursuit trajectories with simulated trajectories based on either pure pursuit, in which the predator steers directly towards its target, or parallel navigation, which enables the predator to intercept prey. Simulations based on pure pursuit consistently provided a better match with the observed trajectories than simulations based on parallel navigation. There was no evidence for an effect of the prey’s predictability on the type of pursuit strategy followed by the predators: pure pursuit was favoured over parallel navigation in the majority of trials, regardless of the predictability of the prey’s initial escape direction. Although our previous research has demonstrated that blue acaras adjust aspects of their behaviour in response to uncertainty about the prey’s likely escape direction, these results show that they maintain the same pursuit strategy, irrespective of the prey’s escape tactics.