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Tiger Shark Sinks its Teeth into Scientific Study

What’s happening in this video?

In this video, a tiger shark investigates and eventually bites an underwater hydrophone that our team set up in the Bahamas to study tiger shark movements. This is part of a larger collaborative research project underway on the behavior and ecology of tiger sharks in the subtropical Atlantic Ocean.

How it works?

These hydrophones, termed “acoustic receivers”, are essentially underwater devices that “listen” for and record acoustic signals emitted from transmitters that are attached to the study animals.

When the animal swims within several hundred meters of the receiver, the device records the presence of the transmitter tag (i.e. the animal) and the time of the detection. To be effective, scientists usually place a series of these receivers, called an array, in strategic locations to detect their study species. Thus, these acoustic tracking tools can provide detailed information on animal movement patterns.

To retrieve the data recorded by the receivers, scientists then have to usually recover and download the data, although new tools allow this to be done wireless and by other means. This differs from satellite tracking, where transmitters send recorded data from tagged animals to orbiting satellites. You can learn about satellite tracking here.

In our tiger shark study, the transmitters we use are very small (only 16 mm, image 1 below), especially when compared to the size of the huge tiger sharks (up to 4 m+). We carefully implant the transmitters inside the shark’s abdomen. To do this, we make a small incision with a scalpel through the shark’s abdominal wall, insert the tag and quickly stitch it back up (Image 2 below). The shark is released and the incision fully heals within days. The transmitters we use have enough battery to transmit for nearly 5 years.

Acoustic Transmitter (Vemco V16).  These transmitters are implanted inside the tiger sharks studied. They hydrophones deployed listen for and record sharks that swim by affixed with these transmitters
Image 1: Acoustic Transmitter (Vemco V16). These transmitters are implanted inside the tiger sharks studied. A quarter is shown next to the transmitter to give an idea of transmitter size.  They hydrophones deployed listen for and record sharks that swim by tagged with these transmitters
Tiger shark interacting with a diver at Tiger Beach. The abdomen of the shark shows stitches at the incision site where the transmitter was implanted. Photo: Lupo Dion
Tiger shark interacting with a diver at Tiger Beach. The abdomen of the shark shows stitches at the incision site where the transmitter was implanted. Photo: Lupo Dion

The great thing about this type of animal tracking technology is that the receivers can detect and record any animal carrying a transmitter, even if from another study and species. For example, our tiger sharks have been detected by receivers in the Bahamas set up to study Bonefish as well as receivers in Florida set up to study lionfish. Likewise, our Tiger Beach array has recorded lemon sharks from Florida and Great Hammerheads from Bimini, Bahamas. This provides a unique opportunity to collaborate, share and obtain data that otherwise could not be available in a single study.

Electronic tagging and tracking of marine animals described above provides invaluable data that can support the conservation of marine species. The Ocean Tracking Network (OTN) is a global partnership that helps support the implantation of acoustic tracking projects around the globe. This includes providing acoustic receivers, expertise as well as a platform for data sharing and collaboration. The mission of OTN is to support sustainable management of valued aquatic species through these efforts.

Comments

  1. Douglas Pincock
    July 10, 2015, 4:29 pm

    I understand your point that the attraction could have occurred only centimeters away but it’s doubtful that field strength would reach even 125 microvolts. It’s more likely to be picovolts (billionths of volts). On the other hand, depending on the sharks hearing abilities (Again I know nothing about this), it might at that short range hear the oscillator which is likely to be essentially a tuning fork

    • Neil Hammerschlag
      July 13, 2015, 2:10 pm

      Douglas. Thanks for the insight. I will investigate further and modify the blog accordingly.

    • Neil Hammerschlag
      July 19, 2015, 1:52 pm

      The latest research suggests that sharks can detect 1 nV/cm

  2. Douglas Pincock
    July 10, 2015, 5:50 am

    Your statement that the shark may have been able to detect the receiver’s electric field seems highly unlikely. In looking at the VR2 data sheet one observes that it achieves 15 months of life with 3.6 Volt/19 amp-hour battery. This works out to an average power consumption of approximately 6 milliwatts. Since the receiver is on continuously, most of this will undoubtedly be direct current which will emit no electromagnetic waves at all.

    The fact that the device keeps track of time does imply the presence of some sort of oscillator which would operate at a frequency of at least a few 10s of kHz creating some kind field but the power required to do this is typically just a few microwatts. Add to this the fact that electromagnetic waves attenuate very quickly in salt water (for example around 7 dB/metre at 32 kHz and higher at higher frequencies) and the implication is that the power level at even three metres from the receiver would but just a few 10s of picowatts. I know nothing of a shark’s ability to detect electromagnetic fields but it does seem a stretch to think they could detect such low levels

    • Neil Hammerschlag
      July 10, 2015, 11:56 am

      Thanks Douglas. This is very useful and informative. I agree (and never suggested) that the shark detected the hydrophone from meters away via electro-sensory means. The shark was first attracted to the vicinity of the receiver through smell since the area was being baited by dive tourist. It likely first detected the receiver through vision. However, while investigating the reviver at close range (centimeters) the shark may well have been able to detect the weak electric signals from the receiver. While the electro-sensory capabilities of sharks are not yet fully understood, white sharks can detect electric fields at least as small as 125 microvolts (millionths of a volt).

  3. Epic Diving
    www.epicdiving.com
    July 10, 2015, 3:23 am

    Interesting article and study Dr. Hammerschlag. It’s great to know that the acoustic array can detect all tags, even from other species and studies. We look forward to seeing your results!