Research Document 2017/041
Comparison of methods to estimate grey seal pup production at different colonies
By Hammill, M.O., Dale, J., Stenson, G.B., den Heyer, C., Gosselin, J.-F., Leblanc, P., and Johnston, D.W.
Abstract
Aerial surveys were flown in January and February 2016 to estimate grey seal pup abundance on Sable Island, along coastal Nova Scotia and in the Gulf of St Lawrence (GSL). Owing to a combination of circumstances (absence of ice in the GSL) and opportunities, different platforms were used to obtain counts of pups on different island colonies. The methods included the use of visual counts, oblique photography from low altitude helicopter flights, photographs using an unmanned aerial vehicle (UAV) and a large format aerial photographic camera. Images from the large format camera were the easiest to count, but this option was the most expensive and presented logistic challenges in coordinating positioning of the aircraft within the four week optimum time for photography of the colonies in the different regions. Images from the UAV were easy to count; the UAV was easy to deploy and did not disturb animals, but flights were limited in some cases by high wind speeds. Images from oblique photographs were suitable for counting, but also provided challenges in ensuring coverage of a colony, particularly if the colony was flat and without obvious landmarks. If only a few pups were present, visual counts were suitable, but at large colonies visual counts underestimated abundance.
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