Fig. 1

Biologging device deployments. a Lactating female Galápagos sea lion (Zalophus wollebaeki) with archival GPS and TDR loggers. Archival loggers are favoured for tropical species as Argos satellite coverage is poor near the equator. VHF transmitter aids re-encounter on the colony for device retrieval. Coded mark-recapture tag shown in the fore-flipper (photo: Jana Jeglinski). b Lactating female Antarctic fur seal (Arctocephalus gazella) with archival video camera (photo: Sascha Hooker). c Argos-CTD telemetry tag deployed on a southern elephant seal (Mirounga leonina) in West Antarctica. This device records both movement and environmental data simultaneously and transmits the data via polar-orbiting satellites, offering valuable data for ecologists and oceanographers alike (photo: Mike Fedak). d GPS-GSM phone telemetry tag deployed on a harbour seal (Phoca vitulina) in the North Sea. These devices are a good option for species that frequent coastal waters in less-remote regions (photo: Sea Mammal Research Unit). Note: for scale, devices pictured in (c) and (d) are roughly the same size