It’s a Drag Wearing a Tag
What impacts do tracking tags have on the behavior and swimming costs of marine mammals?
Electronic devices affixed to individual animals are invaluable tools for researchers studying the lives of wild marine mammals. These data logging “tags” can record the animal’s behavior, physiology, and physical and auditory environment — data that would be unobtainable by other means.
Developments in microcomputer technology have increased the capacity of these devices, but the size of these electronic tags has not decreased as rapidly. This led Dr. David Rosen (UBC) to ask whether the relatively large sizes of electronic tags affects the behavior and swimming costs of individuals being tracked at sea? Surprisingly few studies have quantified the behavioral or energetic effects of tag attachment on marine mammals despite the widespread use of this technology.
Dr. Rosen tested the potential short-term impact of tag attachment with a group of trained northern fur seals held as part of a long-term research program at the Vancouver Aquarium.
Aquarium trainers trained four fur seals to swim between a respirometry dome floating at the surface of a large research pool, down to the opposite bottom of the pool where they were rewarded with a fish, and then to immediately return to the dome where scientists could measure how much oxygen they had consumed (energy they used).
For each trial, the fur seals had to complete this 18.6 m course a total of 5 times in quick succession. By timing the laps, Dr. Rosen’s team could also measure their swimming speed.
To test the effects of wearing a tag, the fur seals had to complete these trials while wearing one of two models of data loggers typically used in field research. Normally, tags are glued directly to the animals’ fur. For this study, the fur seals were outfitted with a Velcro patch that allowed trainers to easily switch between tags for different trials, as well as undertake matching trials without tags.
The results of the study were recently published in the journal Marine Mammal Science. They show that the tags significantly affected both the short-term behavior and energetics of the fur seals, despite the fact that tag mass was <1% of body mass. The animals swam slower and used more energy to swim. As a result, the total cost of swimming the prescribed circuit increased by 12-19%.
As noted in the published paper, the study specifically measured the effects of short-term placement of tags on northern fur seals. Care must be taken when extrapolating the results to long-term deployments in the wild.
However, if the persistence of these short-term effects would potentially bias data sets obtained from wild animals and could even lead to long-term impacts on life history traits.
Dr. Rosen is also quick to note that this study is not a denunciation of using external data loggers. Rather, scientists must consider these potential effects to interpret their data, and guide ethical and scientific designs of future studies.