Evaluating outcomes of long-term satellite tag attachment on leatherback sea turtles

Abstract

Attachment methods for satellite tags deployed on marine animals must optimize data collection and minimize potential adverse effects on the study subjects. The smooth, oily carapace of the leatherback turtle contrasts with the keratinized scutes of other sea turtles and has required the development of novel approaches to tag attachment. Early leatherback satellite tracking work focused on non-invasive methods, namely the use of custom-fitted harnesses, which have now largely been replaced by the direct attachment of tags to the carapace. The present study represents the first long-term assessment of satellite tag retention, recovery, and attachment site condition for leatherback sea turtles. We compare outcomes for female, male, and sub-adult turtles tagged using both harness (n = 43) and direct attachment methods (n = 43) in a foraging area off Nova Scotia, Canada. We demonstrate that the typical operational lifespan of harness-attached tags (median 227 days) was similar to that of directly-attached tags (median 235 days). However, harness tags may be more likely to be lost at high latitudes than directly-attached tags. Mating interactions may be a primary source of tag loss for female leatherbacks because, irrespective of tag attachment method, tracking data suggest that females are more likely to lose their tags at low latitudes than either males or sub-adult turtles. High re-encounter rates (~ 50%) on nesting beaches after tagging in Canadian waters indicate that both female turtles with harness tags and directly-attached tags continue to nest successfully, many in the first nesting season following tagging. Differences in tag attachment methodologies did not appear to affect turtle survival or nesting success; however, follow-up examinations suggested divergence in the scale of impact to contact tissue. Direct attachment was characterized as a benign tagging method, as associated impacts were typically superficial, limited to the footprint of the tag itself, and nearly imperceptible following tag loss. This stands in contrast to harness tags, which have been characterized by impact to multiple body parts in contact with harness materials and potential long-term or permanent disfigurement and/or scarring of the body. Moving forward, we encourage all wildlife telemetry practitioners to continue to optimize tag characteristics and attachment methods to improve animal welfare.