Science Spotlight

Science in Depth:

Improving the LIMPET tag

Project title: Improving attachments of remotely-deployed dorsal fin-mounted tags: tissue structure, hydrodynamics, in situ performance, and tagged-animal follow-upCategories for listing: marine mammals
 
Principal Investigator: Dr. Russ Andrews
 
Collaborators: Robin Baird and Greg Schorr (Cascadia Research Collective), Brad Hanson (Northwest Fisheries Science Center, NOAA), Frank Fish (West Chester University), Laurens Howle (Duke Univ. and BelleQuant Engineering), Rajat Mittal (Johns Hopkins Univ. and Cartesian Flow Solutions), Stephen Raverty (Animal Health Center, B.C. Ministry of Agriculture and Lands), Roger Hill, Shawn Wilton and other staff at Wildlife Computers. 
 
Funding: National Oceanographic Partnership Program and Office of Naval Research
 
Project Synopsis: We recently developed small satellite-linked telemetry tags that are anchored with small attachment darts to the dorsal fins of small- and medium-sized cetaceans. These Low Impact Minimally-Percutaneous External-electronics Transmitter (LIMPET) tags have opened up the potential to monitor the movements of numerous species not previously accessible because they were too large or difficult to capture safely, but too small for tags that implant deeply within the body. One goal of this project is to improve upon our existing tagging methodology to achieve longer, less variable attachment durations by carefully examining the factors that affect attachment success. Our key goal is to develop a method for attaching tags to cetaceans that provides the data needed to answer critical conservation and management questions without an adverse effect on the tagged animal. Therefore, we will also conduct follow-up studies of whales that have been tagged with a remotely-deployed dorsal fin-mounted tag to accurately quantify wound healing and the effects of tagging on whale survival, reproduction, and behavior. The combination of these approaches will provide 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.
 
Approach:
 
1. Hydrodynamics of tag shape: Numerical modeling and analysis, primarily computational flow dynamics, are being conducted in concert with physical experiments to establish qualitative as well as quantitative relationships between tag configuration and the associated flow structure and surface pressure distribution, determining drag and lift forces, with the ultimate goal of reducing the forces that reduce attachment duration.
 
 
2. Dorsal fin tissue structure: We are assessing tissue properties to identify factors likely to influence long-term tissue viability. Interspecific differences in these parameters may be an important factor in the variability in attachment duration. We selected various species for examination based on differences such as size/shape of the dorsal fin (e.g., melon-headed versus killer whale), taxonomic grouping (i.e., odontocetes versus mysticetes), or dynamic behavior (e.g., beaked whale versus melon-headed whale).
 
 
3. Performance of tag attachments – simulated and actual: A key factor in attachment duration is likely the hydrodynamic forces imposed by the tag body but acting on the attachment elements implanted into the dorsal fin. We are using imaging of carcass tissue to determine how the retention elements behave in situ. These results, along with those from the analysis of dorsal fin histology and material properties will inform modified designs. Hundreds of LIMPET tags have now been applied to various species of cetaceans, and we are examining inter-species differences to identify factors that affect tag longevity.
 
 
4. Tagging effects - follow-up studies of survival, reproduction,& behavior: More thorough assessments of the potential impacts on survival and reproduction of individuals, as well as assessment of healing of the tag attachment sites and potential behavioral changes associated with tagging, are needed to address concerns regarding sub-lethal and potentially lethal impacts of remotely-deployed tags. As part of an ongoing collaborative study, over 130 satellite and VHF tags have been remotely-deployed on 9 species of odontocetes around the main Hawaiian Islands. Re-sighting rates for the two species with the largest sample size of tag deployments, short-finned pilot whales and insular false killer whales, are particularly high, as populations are small, individuals are relatively easy to approach, and there are sufficient encounters each year to have a high probability of re-sighting previously tagged whales. We are assessing impacts of remotely-deployed tags on tagged animals at a variety of levels: from wound healing and potential behavioral effects of tag attachment to reproduction and survival.
 

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