Predation domes: In-situ field assays to measure predatory behaviours by fish

Biotic interactions such as predation are difficult ecological processes to quantify in the wild. This is especially the case in the marine environment due to logistical difficulties in capturing animal behaviour. Common approaches use aquarium-based experiments, live-tethering, or assays with bait as proxies for quantifying predation pressure. However, these methods often fail to account for natural interactions between species in the wild and may raise ethical and animal welfare concerns. We designed a novel field-based method to quantify predator-prey interactions for marine fishes. The "predation dome" is a clear acrylic aquarium that contains a live fish. The dome is filmed and, in contrast to other methods, it allows for natural olfactory and visual cues, and the prey fish is returned to the wild after the assay. Here, we provide a step-by-step guide on building and deploying the predation dome in the wild. To demonstrate its use, we quantified predation pressure using the domes in two tropical and two temperate locations. Piscivores were attracted to the domes and displayed predatory behaviours such as circling or striking. Although the overall number of predatory attacks did not differ among locations, predation domes revealed higher predation pressure by piscivores at the tropical locations in comparison to temperate reefs. Our results show that predation domes represent an ethical and complementary approach to measure predation that may better represent piscivory as compared to other behaviours. Predation domes can be also used to measure other biotic interactions such as territorial defence or courtship.