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R Soc Open Sci. 2019 Sep 4;6(9):190296. doi: 10.1098/rsos.190296. eCollection 2019 Sep.

The effect of a multi-target protocol on cetacean detection and abundance estimation in aerial surveys.

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Observatoire PELAGIS, UMS 3462 CNRS - La Rochelle Université, 5 Allées de l'Océan, 17000 La Rochelle, France.
Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine Hannover Foundation, Werftstr. 6, 25761 Büsum, Germany.
Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews KY16 8LB, UK.
Centre d'Études Biologiques de Chizé, UMR 7372 CNRS - La Rochelle Université, 5 Allées de l'Océan, 17000 La Rochelle, France.
Wageningen Marine Research, Haringkade 1, 1976CP Ijmuiden, The Netherlands.


A double-platform protocol was implemented in the Bay of Biscay and English Channel during the SCANS-III survey (2016). Two observation platforms using different protocols were operating on board a single aircraft: the reference platform (Scans), targeting cetaceans, and the 'Megafauna' platform, recording all the marine fauna visible at the sea surface (jellyfish to seabirds). We tested for a potential bias in small cetacean detection and density estimation when recording all marine fauna. At a small temporal scale (30 s, roughly 1.5 km), our results provided overall similar perception probabilities for both platforms. Small cetacean perception was higher following the detection of another cetacean within the previous 30 s in both platforms. The only prior target that decreased small cetacean perception during the subsequent 30 s was seabirds, in the Megafauna platform. However, at a larger scale (study area), this small-scale perception bias had no effect on the density estimates, which were similar for the two protocols. As a result, there was no evidence of lower performance regarding small cetacean population monitoring for the multi-target protocol in our study area. Because our study area was characterized by moderate cetacean densities and small spatial overlap of cetaceans and seabirds, any extrapolation to other areas or time requires caution. Nonetheless, by permitting the collection of cost-effective quantitative data for marine fauna, anthropogenic activities and marine litter at the sea surface, the multi-target protocol is valuable for optimizing logistical and financial resources to efficiently monitor biodiversity and study community ecology.


SCANS-III survey; abundance estimation; aerial surveys; distance sampling; double-platform protocol; perception bias

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