Current studies of fine-scale baleen whale diving and foraging behaviour rely on archival suction cup tags that remain attached over time scales of hours. However, skin irregularities can make suction cup attachment unreliable, and traditional pole deployment of suction cup tags is challenging in moderate sea conditions or when whales are evasive.
We developed a new tag attachment to overcome these limitations. The attachment features a short (6·5–7·5 cm) needle that anchors in the whale's dermis (epidermis and blubber) to which a free-floating tag is attached via a severable tethered link. The needle, tag and a detachable ‘carrier rocket’ with fletching are fitted together to form a projectile that can be deployed at distances of up to 20 m using a compressed-air launcher. A corrosive release mechanism allows the tag to separate from the needle after a specified period of time so that the tag can be recovered.
The dermal attachment was evaluated during a study of humpback whales (Megaptera novaeangliae) in the Gulf of Maine and then subsequently deployed on bowhead whales (Balaena mysticetus) near Barrow, Alaska. Monitoring of tagged humpback whales indicated that the needle was shed several days after deployment, the attachment site healed shortly thereafter, and there were no discernible behavioural or health effects over time scales of days to months after tagging. Bowhead whales showed little immediate reaction to tagging; the most common response was a prolonged dive right after tag deployment. On average, respiration rates of tagged bowhead whales were elevated after tag attachment, but returned to the same rate as undisturbed bowheads within 1–1·5 h.
When compared to suction cups, the dermal anchor provided a more reliable attachment and it can be applied from greater distances and in rougher sea conditions; it is therefore a useful alternative in circumstances where suction cup tags cannot be easily deployed.