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.

Lemon Love

Right, so now that I've been here for almost 2 months, I feel like it's a little strange that I haven't done a post on the one shark I work with pretty much every day.  So without further ado, I bring you the lemon shark.

Lemon sharks are the reason the Bimini Biological Field Station exists.  The man who founded the lab, Dr. Samuel Gruber, has dedicated his life to understanding these sharks.  Right now, we have a Phd. student at the lab conducting her research on juvenile lemon sharks to see how they are affected by the destruction of nursery habitat on Bimini island. Almost everything we do is gathering data for her project.

(Note, the resort called Bimini Bay is kind of the bad guy in all this, but it isn't so simple. The project has brought a lot of jobs to the island but at the same time has destroyed valuable mangrove habitats that the lemon sharks and many other marine species use as a home.  That is what Kristine's project is all about.  What's worse is that the owners of the resort cleared off more land than they could afford to develop in an attempt to attract investors.  Basically they bulldozed about 2 square miles of mangrove forests for no reason other than to make it seem like they were making progress.  Boo them, but do it quietly because Bimini needs the jobs.  Anyways...)

So about the lemon shark...They can grow up to 13 feet long, but generally top out at about 10 feet.  The ones you see in these pictures are juveniles, no bigger than about 2-3 feet long.  That being said, these kids are STRONG.  The second day at the lab, we had a half-day class devoted to how to handle juvenile lemon sharks.  They are fast, strong, and can pack a mean bite if you don't respect them.  Lemon sharks are set apart from other sharks in a few ways.  First, they can pump water through their gills without swimming, allowing them to breathe without moving.  (If you recall, tiger sharks and nurse sharks also share this ability.)  Another defining characteristic is that the first and second dorsal fins (the ones on top, in case you forgot) are almost the same size.  In most sharks, the second dorsal is significantly smaller then the first.

The way to hold them is just behind the gills but in front of the first dorsal fin.  Lemons are extremely flexible, so if you try to hold them anywhere behind the first dorsal, they can whip around and grab on to you.

Here at the lab, we have a bunch of different tasks to perform involving baby lemon sharks; too many for just one post.  From here on out, I'm going to try to do a post a week describing the different things we do to study the sharks.  Originally I thought this would be too boring for most people, but nothing terribly awsome is happening so I want to put something up.  I'll start with tracking, and then move to pen trials, seining, and then eversions (you pull a sharks stomach out through its mouth to see what it has been eating...SO cool.)  I have pictures for tracking, but not enough for seining and eversions, hence the weekly posts and not daily.  That will bring us to the end of March when mini-PIT happens, and that's an entity unto itself.  So until tracking day next week, adieu.