Minimizing the impact of biologging devices: Using computational fluid dynamics for optimizing tag design and positioning. Issue 8 (18th June 2019) - Kay, William P.; Naumann, David S.; Bowen, Hannah J.; Withers, Simon J.; Evans, Benjamin J.; Wilson, Rory P.; Stringell, Thomas B.; Bull, James C.; Hopkins, Phil W.; Börger, Luca
Abstract: Biologging devices are used ubiquitously across vertebrate taxa in studies of movement and behavioural ecology to record data from organisms without the need for direct observation. Despite the dramatic increase in the sophistication of this technology, progress in reducing the impact of these devices to animals is less obvious, notwithstanding the implications for animal welfare. Existing guidelines focus on tag weight (e.g. the '5% rule'), ignoring aero/hydrodynamic forces in aerial and aquatic organisms, which can be considerable. Designing tags to minimize such impact for animals moving in fluid environments is not trivial, as the impact depends on the position of the tag on the animal, as well as its shape and dimensions. We demonstrate the capabilities of computational fluid dynamics (CFD) modelling to optimize the design and positioning of biologgers on marine animals, using the grey seal ( Halichoerus grypus ) as a model species. Specifically, we investigate the effects of (a) tag form, (b) tag size, and (c) tag position and quantify the impact under frontal hydrodynamic forces, as encountered by seals swimming at sea. By comparing a conventional versus a streamlined tag, we show that the former can induce up to 22% larger drag for a swimming seal; to match the drag of the streamlined tag, the conventional tag would have to be reduced in size by 50%. For the conventional tag, the drag induced can differ by up to 11% depending on the position along the seal's body, whereas for the streamlined tag this difference amounts to only 5%. We conclude by showing how the CFD simulation approach can be used to optimize tag design to reduce drag for aerial and aquatic species, including issues such as the impact of lateral currents (unexplored until now). We also provide a step‐by‐step guide to facilitate the implementation of CFD in biologging tag design. Translated abstract: Defnyddir dyfeisiau biogofnodi'n eang iawn ar draws dosbarthiadau fertebratiaid mewn astudiaethau symudiad ac ymddygiad ecolegol i gofnodi data o organeddau heb fod angen arsylwi'n uniongyrchol. Er gwaethaf y cynnydd syfrdanol yn natur soffistigedig y dechnoleg hon, mae'r cynnydd wrth leihau effaith y dyfeisiau hyn ar anifeiliaid yn llai amlwg, er gwaethaf y goblygiadau ar gyfer lles anifeiliaid. Mae canllawiau presennol yn canolbwyntio ar bwysau tag (e.e. y 'rheol 5%'), gan anwybyddu grym aero/hydrodynamig mewn organeddau awyr a dyfrol, sy'n gallu bod yn sylweddol. Nid yw dylunio tagiau i leihau effaith o'r fath i anifeiliaid sy'n symud mewn amgylcheddau llifyddol yn beth bach, gan fod yr effaith yn dibynnu ar leoliad y tag ar yr anifail, yn ogystal â'r siâp a'i ddimensiynau. Rydym yn dangos galluoedd modelu deinameg hylif gyfrifiannol (CFD) i optimeiddio dyluniad a lleoliad biogofnodwyr ar anifeiliaid morol, gan ddefnyddio'r morlo llwyd ( Halichoerus grypus ) fel rhywogaeth fodel. Yn benodol, rydym yn ymchwilio i effeithiau (i) ffurf y tag, (ii) maint y tag a (iii) lleoliad y tag a meintoli'r effaith dan rymoedd hydrodynameg uniongyrchol, fel y mae morloi sy'n nofio yn y môr yn eu profi. Drwy gymharu tag confensiynol â thag llyfn, rydym yn dangos y gall y fersiwn gonfensiynol greu hyd at 22% mwy o effaith lusgo i forlo sy'n nofio; er mwyn efelychu effaith lusgo'r tag llyfn, byddai'n rhaid lleihau maint y tag confensiynol gan 50%. Ar gyfer y tag confensiynol, gall yr effaith lusgo a grëir amrywio hyd at 11%, gan ddibynnu ar ei leoliad ar gorff y morlo, er mai 5% yn unig yw'r gwahaniaeth hwn ar gyfer tag llyfn. Rydym yn cloi wrth ddangos sut gall ymagwedd efelychu CFD gael ei defnyddio i optimeiddio dyluniad tagiau a lleihau'r effaith lusgo i rywogaethau awyr a dyfrol, gan gynnwys materion megis effaith cerrynt ystlysol (nad ydynt wedi'u hastudio hyd yma). Rydym hefyd yn cynnig canllaw cam wrth gam i hwyluso rhoi CFD ar waith wrth ddylunio tagiau biogofnodi.