Assessment of long-distance detection of gillnets by porpoises: Reply to Dawson and Lusseau

Nielsen et al. (2012; Mar Ecol Prog Ser 453:241-248) analyzed surface observations of harbour porpoises in a small coastal area where a modified gillnet was introduced at randomized time intervals. The study concluded that porpoises reacted to the gillnet at surprisingly large distances (in some cases >80 m). Dawson & Lusseau (2013; Mar Ecol Prog Ser 478:301-302) argue that the conclusions of Nielsen et al. (2012) are undermined by pseudo-replication (a matter of concern in many field studies of marine mammals). We acknowledge these concerns, but we think that the conclusions of Nielsen et al. (2012) remain valid, as the data are best explained by harbour porpoises being able to detect and avoid gillnets at very long ranges.