Abstract

Until recently, there were only two options for attaching telemetry devices to small to medium-size cetaceans: short-term attachment with suction cups, or capture and surgical implantation of attachment pins for securing devices. To examine the role of killer whale predation on marine mammal populations in the North Pacific, we needed longer term tracking durations than possible with suction cups, and capture was not an option. Therefore we set out to design a new miniature, low-drag location-only satellite transmitter package and a method for remotely-attaching it to the dorsal fin of whales. We sought an approach that was as minimally invasive as possible with the least likelihood for adverse impact on the whale, but that could still provide at least one month of tracking data. After much iteration, we arrived at a barnacle-type tag (electronics on outside of whale, small implants as attachments) with two barbed titanium darts that penetrate approximately 6.5 cm, now called the Low Impact Minimally Percutaneous External-electronics Transmitter (LIMPET) tag. Tags are deployed using a crossbow or low-powered pneumatic rifle at distances between 3 and 20 meters from the dorsal fin. Initial applications of LIMPET tags on killer whales in Alaska provided transmissions ranging from 1–90 days (median ~ 1 month). In every case where we have resighted the pod of a tagged Alaskan killer whale, the tagged whale was also resighted. Within 6 months after tag loss, most resighted Alaskan whales had small (< 3 cm) well-healed scars at the dart penetration sites. The success of the LIMPET tag led to its use on 20 species of cetaceans, many of which had never before been tracked via satellite. We are currently conducting a multi-collaborator study to improve LIMPET tagging methods to achieve longer, less variable attachment durations without adversely impacting whales by carefully examining the factors that affect attachment success. We are assessing the hydrodynamic properties of our current tag shapes and new candidates that may reduce the drag and lift forces that pull on the tag. We are also conducting histological and material properties analyses, including collagen density, fiber geometry and strength in multiple species. The holding power and in situ behavior of attachment darts and barbs in carcass tissue is being examined with dynamic load tests and x-ray and MRI scans. We are also conducting follow-up studies of tagged whales to accurately quantify wound healing and the effects of tagging on whale survival, reproduction, and behavior. Healing of tag attachment sites and dorsal fin thermoregulatory function is examined using high-resolution photos and Forward Looking InfraRed (FLIR) imaging. (For example, preliminary FLIR results confirm that LIMPET tagging does not compromise the ability of the fin vasculature to radiate heat). We are also comparing relative survival rates of tagged and non-tagged short-finned pilot whales and false killer whales using photographic re-sightings. This combination of approaches is providing an improved understanding of some of the key factors affecting tag attachment duration as well as a more complete understanding of impacts to individuals due to tagging.

* Presenting author