Abstract
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.
Highlights
Unbiased estimates of the abundance of wildlife populations are necessary for effective conservation and for the management of human activities
The double-platform protocol was implemented during the SCANS-III survey in 2016 to test for a potential bias in small cetacean estimation when operating the megafauna protocol used during several marine aerial surveys
The double-platform protocol was previously tested during two pilot studies in 2012 and 2014 (SAMM and SAMM-ME), but the amount of effort achieved resulted in too few sightings to allow sufficient statistical power to reliably identify any potential bias in small cetacean detection due to the detection of other animals
Summary
Unbiased estimates of the abundance of wildlife populations are necessary for effective conservation and for the management of human activities. Megafauna population estimation is mostly achieved through boat-based or aerial surveys using a dedicated protocol based on distance sampling methodology. The targeted species in a monotarget protocol are typically a grouping of species with similar characteristics that it is effective to survey at the same time, e.g. cetaceans or seabirds. Multi-target surveys are increasingly being undertaken in marine systems, effectively surveying a range of taxonomic groups [5,6,7,8]. In the context of optimizing marine wildlife monitoring, multi-target surveys have the great advantage of permitting cost sharing and reducing the ecological footprint compared with monotarget surveys [9,10]. Survey data of multiple taxonomic groups collected simultaneously are relevant to understanding ecological relationships among ecosystem components, which is fundamental for the implementation of monitoring programmes [11,12,13]
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