Aerial surveys for Antarctic minke whales (Balaenoptera bonaerensis) reveal sea ice dependent distribution patterns
Herr, Helena ; Kelly, Natalie ; Dorschel, Boris ; Huntemann, Marcus ; Kock, K. ; Lehnert, Linn Sophia ; Siebert, Ursula ; Viquerat, Sacha ; Williams, Rob ; Scheidat, Meike - \ 2019
Ecology and Evolution 9 (2019)10. - ISSN 2045-7758 - p. 5664 - 5682.
Antarctic minke whale distribution - density surface models - distance sampling - marginal ice zone - ship-based helicopter surveys - southern ocean
This study investigates the distribution of Antarctic minke whales (AMW) in relation to sea ice concentration and variations therein. Information on AMW densities in the sea ice‐covered parts of the Southern Ocean is required to contextualize abundance estimates obtained from circumpolar shipboard surveys in open waters, suggesting a 30% decline in AMW abundance. Conventional line‐transect shipboard surveys for density estimation are impossible in ice‐covered regions, therefore we used icebreaker‐ supported helicopter surveys to obtain information on AMW densities along gradients of 0%–100% of ice concentration. We conducted five helicopter surveys in the Southern Ocean, between 2006 and 2013. Distance sampling data, satellite‐derived sea‐ice data, and bathymetric parameters were used in generalized additive models (GAMs) to produce predictions on how the density of AMWs varied over space and time, and with environmental covariates. Ice concentration, distance to the
ice edge and distance from the shelf break were found to describe the distribution of AMWs. Highest densities were predicted at the ice edge and through to medium ice concentrations. Medium densities were found up to 500 km into the ice edge in all concentrations of ice. Very low numbers of AMWs were found in the ice‐free waters of the West Antarctic Peninsula (WAP). A consistent relationship between AMW distribution and sea ice concentration weakens the support for the hypothesis that varying numbers of AMWs in ice‐covered waters were responsible for observed changes in estimated abundance. The potential decline in AMW abundance stresses the need for conservation measures and further studies into the AMW population status. Very low numbers of AMWs recorded in the ice‐free waters along the WAP support the hypothesis that this species is strongly dependent on sea ice and that forecasted sea ice changes have the potential of heavily impacting AMWs
Aerial surveys of cetaceans and seabirds in Irish waters : occurrence, distribution and abundance in 2015-2017
Rogan, E. ; Breen, P. ; Mackey, Mick ; Cañadas, Ana ; Scheidat, M. ; Geelhoed, S.C.V. ; Jessopp, Mark - \ 2018
Department of Communications, Climate Action & Environment - 298 p.
observe programme - aerial survey - cetacean - seabird - abundance - density - megafauna - distance sampling - Ireland - Atlantic - Celtic Sea - Irish Sea
A simple method for estimating the effective detection distance of camera traps
Hofmeester, Tim R. ; Rowcliffe, J.M. ; Jansen, Patrick A. - \ 2017
Remote Sensing in Ecology and Conservation 3 (2017)2. - ISSN 2056-3485 - p. 81 - 89.
Body mass - camera traps - distance sampling - passive infrared sensor - sensor sensitivity - trail camera
Estimates of animal abundance are essential for understanding animal ecology. Camera traps can be used to estimate the abundance of terrestrial mammals, including elusive species, provided that the sensitivity of the sensor, estimated as the effective detection distance (EDD), is quantified. Here, we show how the EDD can be inferred directly from camera trap images by placing markers at known distances along the midline of the camera field of view, and then fitting distance-sampling functions to the frequency of animal passage between markers. EDD estimates derived from simulated passages using binned detection distances approximated those obtained from continuous detection distance measurements if at least five intervals were used over the maximum detection distance. A field test of the method in two forest types with contrasting vegetation density, with five markers at 2.5 m intervals, produced credible EDD estimates for 13 forest-dwelling mammals. EDD estimates were positively correlated with species body mass, and were shorter for the denser vegetation, as expected. Our findings suggest that this simple method can produce reliable estimates of EDD. These estimates can be used to correct photographic capture rates for difference in sampling effort resulting from differences in sensor sensitivity between species and habitats. Simplifying the estimation of EDD will result in less biased indices of relative abundance, and will also facilitate the use of camera trap data for estimating animal density.