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State of the Field: Satellite tagging sharks

Modern shark researchers have access to a variety of high-tech tools. Acoustic tags with noises specific to each individual shark signal a receiver (or network of receivers) every time the shark passes nearby. Some tags have three-dimensional accelerometers, allowing researchers to study the small scale movement patterns and behaviors of sharks. Others, which are placed in the stomach, measure pH before, during, and after digestion. The most advanced technology on the market, however, is undoubtedly the satellite tag.

Image from SurfThereNow.com

Satellite tags are usually mounted to the shark’s dorsal fin. One type of tag, used on species that often spend their time near the surface (i.e. great whites, whale sharks, etc) transmits data to orbiting satellites whenever the tag breaks the surface. Another type, known as a pop-up tag, is used on species unlikely to visit the surface. Instead, pop-up tags detach from the shark after a pre-programmed amount of time, float to the surface, and transmit all their data at once.

Image Courtesy Seychelles Marine Conservation Society

Satellite tags can record a variety of different kinds of data, including location, water temperature, and depth. Depending on how many sensors are involved, the cost per tag can be several thousand dollars. This can generate important data concerning sharks’ migration patterns, feeding behaviors, and habitat requirements. If they work properly (always a big “if” when dealing with new technology), they can record and transmit data for months or even years.  Though this kind of research can generate headlines (such as the tracking of Nicole, the great white shark who swam from South Africa to Australia and the discovery that basking sharks migrate from New England to South America), it often isn’t really hypothesis testing.

Shark scientist Dr. Chris Lowe refers to such studies as “shiny new hammer” science- in essence, researchers have a shiny new hammer and they are trying to hit as many nails as they can with it without first thinking about what the best way to use that hammer is. In a review of shark satellite tagging studies, Dr. Neil Hammerschlag referenced such studies as attempting to “‘see what the sharks do’ or ‘where they go'”.

According to Dr. Hammerschlag’s review, 48 studies to date have used satellite tags to study sharks and most qualify as “shiny new hammer” science. These have focused on 17 species, though half of them have involved  just three species (great white sharks, whale sharks, and basking sharks). Approximately 10% of tags failed, and 39 out of these 48 studies had at least one tag that didn’t work properly, which should be taken into account by anyone planning to use this expensive technology in their own research. The review also noted that the color of the tags can have a major impact on the behavior of the tagged sharks- animals that rely on stealth to hunt are disadvantaged by a piece of bright orange plastic sticking to them.

The data gathered by “shiny new hammer” research can be incredibly useful to the science and conservation community- improved knowledge of migration paths can aid conservation policymakers. That said, using this technology to test hypotheses and answer important questions would be more valuable than using it for this kind of data collection and I hope to see more of that in the future.

Image from Shaaark.com

ResearchBlogging.org

Bonfil, R. (2005). Transoceanic Migration, Spatial Dynamics, and Population Linkages of White Sharks Science, 310 (5745), 100-103 DOI: 10.1126/science.1114898

Hammerschlag, N., Gallagher, A., & Lazarre, D. (2011). A review of shark satellite tagging studies Journal of Experimental Marine Biology and Ecology, 398 (1-2), 1-8 DOI: 10.1016/j.jembe.2010.12.012

Papastamatiou, Y., Meyer, C., & Holland, K. (2008). A new acoustic pH transmitter for studying the feeding habits of free-ranging sharks Aquatic Living Resources, 20 (4), 287-290 DOI: 10.1051/alr:2008003

Skomal, G., Zeeman, S., Chisholm, J., Summers, E., Walsh, H., McMahon, K., & Thorrold, S. (2009). Transequatorial Migrations by Basking Sharks in the Western Atlantic Ocean Current Biology, 19 (12), 1019-1022 DOI: 10.1016/j.cub.2009.04.019

Whitney, N., Pratt, H., Pratt, T., & Carrier, J. (2010). Identifying shark mating behaviour using three-dimensional acceleration loggers Endangered Species Research, 10, 71-82 DOI: 10.3354/esr00247