Telemetry tags increase the costs of swimming in northern fur seals, Callorhinus ursinus

Abstract

Animal‐borne instruments have become a standard tool for collecting important data from marine mammals. However, few studies have examined whether placement of these data loggers affects the behavior and energetics of individual animals, potentially leading to biasing data. We measured the effect of two types of relatively small data loggers (<1% of animals’ mass and front profile) on the swimming speeds and energy expenditure of four female northern fur seals (Callorhinus ursinus) while swimming at depth. Swim speeds and rates of oxygen consumption were measured as the trained fur seals repeatedly swam an underwater circuit, with or without the tags. We found the placement of either tested tag significantly affected both the behavior and energetics of the fur seals in our study. Diving metabolic rate increased an average of 8.1%–12.3% (depending on tag type) and swim speed decreased an average of 3.0%–6.0% when wearing the tags. The combined changes in velocities and metabolic rates resulted in a 12.0%–19.0% increase in the total energy required by the fur seals to swim a set distance. The demonstrated effects of tags on behavior and energy expenditure may bias data sets from wild animals and potentially incur longer‐term impacts on the studied animals.

Minimizing the impact of biologging devices: Using computational fluid dynamics for optimizing tag design and positioning

“…Finally, most existing guidelines for tag impact do not advise on appropriate tag size, placement positions or configurations (Rosen et al, ) and many are relatively naïve to the impacts of drag that are most relevant to marine and aerial applications (see Appendix for an overview). We anticipate that the reporting of drag values in future publications may help improve future guidelines and address recent requests in the literature for improved reporting of impacts (Bodey et al, ; Lameris & Kleyheeg, ) and better assessment of tag‐induced effects (such as drag) prior to deployment in the field (Lear et al, ).…”

“…Hence, minimizing tag footprint is important, and this further exemplifies the usefulness of using CFD to efficiently and quickly evaluate the pros and cons of different tag design and size choices. It is also important to note that the effect of tag-induced drag is likely to be greater as the ratio of tag to animal volume increases (Kyte et al, 2018), and minimizing tag frontal cross-sectional area should also be undertaken where possible (Rosen et al, 2017). Ultimately, to reduce drag, tags should be designed to be more streamlined in line with the contours of the animal being tagged to achieve smooth flow reattachment downstream of the tag (see tag B; Figure 4).…”

“…Finally, most existing guidelines for tag impact do not advise on appropriate tag size, placement positions or configurations (Rosen et al, 2017) and many are relatively naïve to the impacts of drag that are most relevant to marine and aerial applications (see Appendix S7…”

“…Despite this, most studies using tags have so far largely failed to take advantage of technological advancements to reduce the impact of tags on animals (Portugal & White, 2018). Crucially, for projects involving tags on aerial and aquatic animals, the focus on weight by most existing tag guidelines -for example the 3% or 5% rule (Casper, 2009) -ignores aero/hydrodynamic impacts (most notably drag) which are key in modulating energy expenditure and behaviour during swimming (Cornick, Inglis, Willis, & Horning, 2006;Culik & Wilson, 1991;Rosen, Gerlinsky, & Trites, 2017;van der Hoop et al, 2018) and flight (Bowlin et al, 2010;Pennycuick, Fast, Ballerstädt, & Rattenborg, 2012; but see Tomotani, Bil, Jeugd, Pieters, & Muijres, 2019). This may lead to biased data which are not representative of freely moving animals (Barron, Brawn, & Weatherhead, 2010;Lear, Gleiss, & Whitney, 2018;Ropert-Coudert et al, 2000), as well as raising important ethical concerns for the animal being tagged (Wilson & McMahon, 2006).…”

“…These approaches are beneficial insofar as during live experiments, it is possible to observe how animals react to tags under real operational conditions (cf. Pavlov & Rashad, 2012;van der Hoop et al, 2018), as well as assessing animal energetics, kinetics and biomechanics, and changes in these over time (Geertsen, Teilmann, Kastelein, Vlemmix, & Miller, 2004;van der Hoop et al, 2018;Ropert-Coudert, Knott, Chiaradia, & Kato, 2007;Rosen et al, 2017). However, experimental approaches are limited in that they are very time-consuming and labour-intensive, wind or flume tunnels are not always accessible, and the use of live animals raises ethical concerns and requires appropriate licensing (Kyte, Pass, Pemberton, Sharman, & McKnight, 2018).…”