Effects of satellite-linked telemetry tags on humpback whales in the Gulf of Maine: photographic assessment of tag sites
Hundreds of large whales have been tracked using consolidated (Type-C) satellite tags, yet there have been few studies on their impacts on whale health. In 2011, we initiated the first study designed to evaluate the effects of these tags in a baleen whale. Between 2011 and 2018, we tagged 79 North Atlantic humpback whales in the Gulf of Maine. We initially deployed commonly-used tags with an articulation between the anchor and transmitter (n=35, 2011-2012). However, evidence of breakage prompted the development and use of more robust, integrated tags (n=45). Tagged individuals were photographed immediately prior to, during and up to 11 years after tagging. They were re-encountered on an average of 41.3 days (SD=44.3), yielding 2,971 photographed sightings through 2022. An objective scoring system was developed to characterise tag site tissue responses based on photographs and to identify risk factors for prolonged healing. The initial tissue response to tagging was minimal, followed by skin loss around the tag, sometimes a degree of swelling, occasional extrusion of blubber, changes in skin colour, local depression formation, tag loss and skin healing over the tag site, sometimes with a depression remaining. At last sighting, most non-integrated and integrated tag sites exhibited small shallow skin depressions (58.8% and 66.7%, respectively). Some exhibited deeper depressions with differing adjacent skin coloration (26.5% and 15.6%, respectively) or barely detectable marks (11.8% and 15.6%, respectively). Mild swellings occasionally persisted at the tag site, but this was uncommon for both tag designs (2.9% and 2.2%, respectively). More severe tissue responses were associated with non-integrated tags and placements lower on the body. This study highlights the importance of using robust tag designs to minimise negative effects from Type-C tags. Furthermore, because tag placement was shown to affect outcome, precision equipment, experienced taggers and vessel operators are critical for optimal deployments.