Counting the cost of tagging : quanitifying and reducing the behavioural and energetic impacts of tags in a large marine vertebrate

Abstract

Despite the invaluable contribution of animal-borne sensors to research, an underlying issue with their use is the potential to impact the behaviour and energetics of instrumented animals, which could have consequences for both animal welfare and data validity. Here I show that the presence of a SMRU GPS/GSM phone tag affects the behaviour and energetics of harbour seals (Phoca vitulina) and grey seals (halichoerus grypus). To reduce the impacts of tagging a computational fluid dynamic (CFD) modelling exercise was undertaken to quantify and describe the additional drag from a phone tag, which informed the redesign of a ‘new’ low drag phone tag. Central to the CFD modelling exercise was a biological relevant and spatially accurate geometry of a swimming harp seal (Pagophilus groenlandicus) generated by a three dimensional (3D) photogrammetrical methodology, developed and calibrated on sea carcasses. CFD modelling predicted additional drag from a phone tag on a 100kg harp seal was 16%. Tag redesign generated a more streamlined tag that reduced tag induced drag by 46%. Comparing the behaviour and energetics of juvenile grey seals carrying the ‘new’ or existing phone tag showed that despite significant reductions in drag resulting from redesign, there was limited amelioration of behavioural impacts and no reduction in the impact on energetics. To better understand the energetics of diving seals, a novel animal-borne sensor was developed. The sensor (PortaSeal) used non-invasive near-infrared spectroscopy ot measure the haemodynamics and oxygenation in the brain and blubber of juvenile harbour seals. Data from the PortaSeal provided numerous insights into the haemodynamic basis of oxygen management of phocid seals.