Background Biologging technologies have yielded new insights into the ecology and behaviour of elasmobranchs, but to date, most studies involve animal capture and restraint to attach tags. Capturing animals usually results in a period of atypical behaviour after release and is undesirable or simply not possible for large and vulnerable elasmobranchs such as mobulas and whale sharks. To avoid animal capture and restraint, we developed and tested two non-invasive multisensor towed tags. The use of towed packages creates additional data analytical challenges relative to fixed packages because towed devices wobble independently of animal movements. We present five examples, two mobulas (reef manta and sicklefin devil ray) and three sharks (blue, tiger and whale shark), to illustrate the advantages and challenges of this approach. We used animal-borne video to validate behavioural data derived from accelerometers and conducted an experiment to compare accelerometer data from attached and towed tags simultaneously deployed on a shark. Results We used fluid dynamic models to calculate the added drag of towed devices on target species. We found that drag impact is acceptable for short-term tagging of large mobulas, but the drag penalty associated with the current camera tag design is greater than 5% for most mature blue sharks. Despite wobble effects, swimming behaviour (tail-beat and wing-stroke frequency) captured by towed accelerometers was consistent with those attached directly to the animal and with data from animal-borne video. Global Positioning System (GPS) sensors recorded up to 28 and 9 geolocations per hour of surface swimming by sicklefin devil ray and blue sharks, respectively. Conclusions Towed tags with non-invasive attachments provide an effective alternative for acquiring high-resolution behaviour and environmental data without capturing and handling animals. This tool yields great potential to advance current knowledge of mobula ecology and behaviour without capture or invasive tagging.

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As regional endotherms, lamnid sharks can sustain high cruising speeds and perform frequent speed bursts. However, since endothermy comes with high energetic costs, lamnids may adopt different swimming strategies to manage their energy budget. Understanding such strategies is essential to provide behavioural and physiological context to their broader movement ecology. The endangered shortfin mako ( Isurus oxyrinchus ) possibly has the highest energy requirements among lamnids, but our understanding of its swimming behaviour is still limited. We equipped three shortfin mako sharks with high-resolution multi-sensor tags to measure their swimming kinematics in the wild. While swimming horizontally, individuals favoured tail-beat frequencies around 0.6 Hz at speeds comparable to those of ectothermic sharks ( ca 0.5 m s −1 ). All individuals displayed yo-yo-like diving patterns where, for a given tail-beat frequency, speeds were higher during descents, as expected for a negatively buoyant fish. Contrary to what was expected, gliding was almost absent (less than 1.31%). Speed bursts reaching up to 3.6 m s −1 were observed during the day but ceased shortly after dusk, implying a diel change in swimming behaviour. As large-scale research efforts are hindered by this species' increasing rarity, opportunistic high-resolution datasets, like the present, are fundamental to improve our understanding of shortfin mako's behaviour and ecology.