226 Sharks: The Animal Answer Guide
shark’s back, or inserted via small harpoons into back musculature. Ultra-
sonic tags that transmit frequency-coded signals are one such technology.
At first, these methods required researchers to sit for hours in small boats,
maps on their laps, listening through hydrophones (underwater receivers)
and recording the location whenever they were lucky enough to hear the
animal’s “pinger.” The data collected were usually relatively short-term be-
cause of battery life and researcher fatigue issues. Vast improvements in-
clude better, longer-lasting batteries and arrays of recording hydrophones
placed on the seafloor. The hydrophones are retrieved by divers after weeks
or months, and the data are then downloaded.
Most recently, advances have allowed the development of satellite track-
ing and “archival” tags that periodically record depth, temperature, and
geological location of the tagged animals. Some tags transmit data to satel-
lites whenever a shark comes to the surface; others eventually pop up and
send out a signal that allows researchers to physically retrieve the tag and
access the incredible storehouse of encoded information. Such tags have al-
lowed us to follow intimately the long-term and long-distance movements
of such animals as White, Basking, Blue, Bull, Tiger, Salmon, Shortfin
Mako, and Whale sharks, and numerous smaller sharks and rays that un-
dergo less spectacular but equally informative movements. For an example
of such a program, see the website Tagging of Pacific Predators (TOPP) at
http://www.topp.org.
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