Tracking

As promised, though maybe delayed, this is the first installment of the "techincal" aspects of the shark lab.  Actually, this post will be about what I do a majority of the time that I'm here because the Phd. candidate is doing her project on the movements of juvenile lemon sharks in relation to mangrove forests.  As mentioned before, the North Sound of Bimini has been stripped of a large fraction of its mangroves to make room for the Bimini Bay resort.  Not to give anything away, but there is a sizeable difference in the movement patterns before and after construction.

Anyways, the way we monitor the movements of sharks is fairly simple.  There are currently 10 baby lemon sharks swimming around with acoustic transmitters implanted in their body cavities.  The transmitter emits a high-frequency signal, which the sharks can't hear or feel, which is then picked up by our hydrophones and made audible to us by a receiver.  What's a hydrophone you ask?

This is a hydrophone.  We sit on the front of our skiffs...

(these are our skiffs) and stick the hydrophone in the water and listen for a signal from a shark that carries a transmitter.  Basically when the hydrophone is pointed at a shark that has a transmitter, it picks up the signal and is attached to a receiver which is attached to our heads with a pair of headphones.  The closer you are to the shark and the more on-target you are with the hydrophone, the louder the signal.  The signal is a series of numbered beeps unique to each shark.  For example, one transmitter pulses out a series of 4 beeps, then a short silence, then 7 beeps, then another silence, then 8 beeps followed by a long silence.  The process then repeats, resulting in this shark being ID'd as 478.  So tracking looks a little something like this...

As you can see, the shark we are tracking in this picture (that little sliver of dark dead center) is extremely close to the boat and my friend Mike here is giving the "put the boat in neutral, you're gonna run over the shark" signal (clenched fist).  The receivers have a range of about 60 meters (about 200 feet for those metrically impaired), so most of the time we can't actually see the shark and just have to rely on our ears.

Tracking crews consist of 3-4 people, a driver, a tracker and a person to record the data (if there is a 4th, there's a person on break).  Once a shark is identified, every 5 minutes the data person records the time, GPS coordinates, bearing and distance to the shark (in what direction and how far away it is in relation to the boat), sea floor composition, amount of cloud cover,  and salinity (how salty the water is).  Now, it isn't always easy like you see above, sometimes you track more than one shark at the same time and you have to distinguish between overlapping beeps of different pitches.

 (sharks are just right of the right shirt sleeve and more or less dead center just below the dark patch on top)
Also, sometimes the weather kind of sucks.

This is Michelle's sad rainy face.
And sometimes the weather really sucks and you forget your rain gear...

Winds gusting up to 55 knots (about 65 mph) out of the north (COLD) + torrential rains = never EVER forget to bring your rain gear, no matter how nice it is in the morning.  But for every crappy day of tracking, there's a lot more good days, and sometimes even a fantastic one.

Sitting on a boat for 8 hours in a tropical paradise with 2 or 3 good friends doing work that will help better our understanding of one of the coolest animals on the planet ending in a sunset like this...yeah, you kind of forget those bad tracking days.