Sequential movement into coastal habitats and high spatial overlap of predator and prey suggest high predation pressure in protected areas

Abstract

In theory, predators should attempt to match the distribution of their prey, and prey to avoid areas of high predation risk. However, there is a scarcity of empirical knowledge on predator and prey spatial use when both are moving freely in their natural environment. In the current study, we use information collated on a predators’ diet, its population structure, as well as predator and prey relative abundance, and track the movements of predator and prey simultaneously to compare habitat use and evaluate predation pressure. The study was conducted in elasmobranch protected areas of coastal Tasmania, Australia. The species considered were the broadnose sevengill shark Notorynchus cepedianus, the apex predator in the area, and five chondrichthyan prey species. Notorynchus cepedianus and its prey show similar seasonality in the use of these coastal areas: more abundant in warmer months and absent in winter. Predator and prey also showed high spatial overlap and similar habitat use patterns. These similar movement patterns of predator and prey combined with the additional ecological information (diet, population structure of predator, relative abundance of predator and prey) suggests that N. cepedianus move into coastal areas to exploit seasonally abundant prey. Also, while in protected areas, chondrichthyans are subjected to high predation pressure. Overall, results illustrate the value of simultaneously recording and integrating multiple types of information to explore predator–prey relationships and predation pressure.