Importance of multi-sensor observations to advance species co-occurrence knowledge: a demonstration of two acoustic technologies

Abstract

Multi-sensor observations, integrated across time and space, may bridge knowledge gaps in ecosystem dynamics, one aspect of which is species co-occurrence. In the present work, we combined data streams from 2 acoustic technologies; passive acoustic monitoring (PAM) and acoustic telemetry (AT) jointly installed under the LifeWatch project. We made use of existing long-term data series from studies on single-species dynamics, to investigate the co-occurrence of multiple species: European seabass, Atlantic cod and cetaceans (harbour porpoise and dolphins), in the Belgian part of the North Sea. Common co-occurrence analyses were applied to a combined PAM and AT hourly presence-absence matrix at different spatial and temporal resolutions. The fish species were in the presence of harbour porpoise at least one-third (seabass) to nearly half (cod) of the time they were detected. At a seasonal resolution, we did not observe probabilities of occupancy to be higher or lower than what is expected by chance, while we could discern patterns of co-occurrence when using an hourly resolution. Analyses done at an hourly resolution showed that porpoises have a significantly higher probability of co-occurrence with cod or seabass during autumn and winter nights. Developing these large-scale networks of integrated acoustic instruments while considering species co-occurrences would further expand data applicability. Considering co-occurrence in ecological research is a step towards ecosystem-based management of our oceans.