Shark Dive

When volunteers first arrive at the lab, the first thing they do is get whisked away to Triangle Rocks for a shark dive before they can even ask, "is this safe"? Fortunately, the kind of people that voluntarily go to a place called the Shark Lab are generally people who find the idea of swimming in the middle of a feeding frenzy cool.

Just south of Bimini is an area called Triangle Rocks, cleverly named because three rocky outcrops form more or less of a triangle. Just to the western edge of the triangle is "the arena," a sandy area in about 20 feet of water where we anchor up the boats for the shark dive.

These feedings have been going on for so long that the sharks usually start showing up when they hear the boat engines, well before any food is thrown into the water. Most are Caribbean Reef Sharks, plus a few Blacknose.

Once anchored, a line is trailed out behind the boat. Decked out in snorkel gear, armed with underwater cameras, everyone slips into the water and hangs onto the line, shoulder to shoulder. The idea is to create an illusion of one big mass of people so the sharks don't try and swim between anyone. (Of course, once when I did this, some space opened up between two people on one side of me, and I looked over just in time to see a 5-ft reef shark bully his way between their shoulders. GREAT photo op. )

Small pieces of cut up fish are thrown into the water in front of the line of snorkelers, and the sharks go to town in front of us. Usually, around 10 sharks show up, and they range in size from about 4ft to about 6ft.

The sharks pretty much stick to the area where the food is being thrown in, but occassionally they get a little too close to the line of snorkelers. If so, we're told to kick them. However, they usually don't get close enough to actually make contact with because the sight of a big fin coming at them or even just the pressure wave from our fins is enough to make them turn around. (I've only had to truly kick one once, and that was because I was looking the other way and didn't see that it was right on me until I turned around.)

After a while, the sharks are full, and they stop immediately attacking the food as it's thrown in. At that point, we all let go of the line and swim feely among the sharks. Unfortunately, once they're fed, they don't really have much interest in sticking around when all these crazy humans are swimming around trying to take pictures of them. They hang around for a bit, circling near the bottom, but eventually they swim off.

In the area around the "arena", you will see a TON of triggerfish, maybe an eel in the rocky ledge near the bottom, sea fans, and sometimes a stingray passing through.

A lot of people, including myself, have mixed feelings about these shark dives. It's clearly not a natural scenario, so even though it's certainly cool to see all these sharks, the experience loses something because it's artificial. However, there are specific instances when the ability to pull in the sharks is helfpful. For example, Shark Defense, Inc. is testing its experimental shark repellant, and to have an area where they can readily bring in sharks is incredibly useful. Once, when I was out on a repellant test with the Chemical Brothers, as they call Mike and Eric, the sharks came in as usual, Eric hopped into the water with a Ghostbusters-style jetpack full of repellant on his back, and the sharks bolted as soon as he released the chemical. Sadly, I don't have a picture of Eric's ridiculous contraption. But the point is, for experimental purposes, the availability of the sharks at Triangle Rocks can be helpful.

A Workup

Most of the work at the Shark Lab has historically focused on the lemon shark, and over the years, standard procedures for taking data when one is caught have been developed. Some of the ways the sharks are caught include gill netting, long-lining and old-fashioned rod and reel. What follows is a description of how juveniles are "worked up".

Let's say, for example, a few juveniles are needed for observation. First we might set a gillnet perpendicular to the shore by tying one end to the mangroves and the other to a rebar stake. When a shark is caught and we intend to temporarily keep it in a pen behind the lab, it is placed in a "transport box" and driven over to the pen. We can then go back to the pen at any time to start a workup.

For a workup, we drive one of the Carolina Skiffs out to the pen (which is about chest-deep at high tide) and anchor up. On the boat we have dip nets, a scale, a measuring trough, PIT tags and PIT tag reader, and other equipment necessary for the workup. First, a dipnet is used to scoop up the shark in the pen. Someone will then reach into the net and hold the shark behind its head, in front of the first dorsal fin. The shark is held just under the surface of the water and walked over to the boat, where a measuring trough filled with water is waiting.

The trough, a PVC pipe sliced lengthwise in half, has a ruler along the bottom. Three measurements are recorded: precaudal lenth (PCL), fork length (FL) and total length (TL). PCL is measured from the tip of the nose to the notch just before the shark's caudal (tail) fin; FL is measured from the tip of the nose to the fork in its tail; and TL from the tip of the nose to the tip of its tail.

A PIT tag reader is waved in the vicinity of the first dorsal fin, where PIT tags are always implanted. If the shark has been caught and tagged before, the reader beeps and displays a number. This number is recorded, and all of the data will be entered into its already-existing section of a master database. If there is no beep, a new PIT tag is implanted. To do this, a tiny incision is made with a scalpel just below the base of the first dorsal fin. A syringe is loaded with a PIT tag, and it is injected into the incision. The number of the tag is recorded, and the shark will be added to the database.

It may be necessary to take a DNA sample from the shark. There are several ways to take a sample, and the most common ways are by clipping the corner off of a fin with scissors or by using a small hole-punch in its tail fin.

The status of the umbilical scar is noted by turning the shark over and seeing if it is open (a newborn), just closed (a little older) or closed. The sex of the shark is also recorded (males have two claspers).

The sharks are weighed using a hand-held scale. One
person holds the scale while another lifts the shark out of the measuring trough and places it in the scale trough.

Finally, observations are made about the condition of the shark: stress (there are signs such as white gills), fin rot (very common - tips of fins look discolored and/or tattered), any scars or other distinguishing characteristics, etc.

Once all measurements have been made, the shark is either walked back to the pen or released, depending on what needs are. All of the data is recorded in a standard format in log books and later added to the master database at the lab. It's through careful measurements like these that things like growth rates have been able to be calculated. If you catch a shark one day and measure it, then you catch the same shark again a year later, you know exactly how much it has grown in one year. Multiply this by the incredible number of sharks in the database, and you have a great snapshot of the overall population.

Bimini: Round 2

I couldn't stay away. The two months I spent at the Shark Lab in September and October of last year were so incredible that I have to go back. Luckily, they'll have me. For the month of June, I'll be back at the lab in bimini for PIT.

PIT (Passive Integrated Transponder) is the annual tagging program the lab runs, where for 3 weeks, juvenile lemon sharks are caught, tagged and released. (For more info on the program, click here.) Gillnets are set overnight for 12 hour periods (a full tidal cycle), and we'll sit out in the lagoon all night catching the sharks and working them up (tagging, measuring, weighing, etc.). Why? Good question. Here's an abridged version of the answer on the Shark Lab's website...

What it came down to for us was to assume that we had no immigration or emigration in the lagoon/nursery where we were studying young lemon sharks. We also assumed no fishing--only natural mortality. Then we chose a sure sampling procedure: We caught and tagged every last lemon shark in the nursery.

We fish the same stations for six nights: The first night we get maybe 65 sharks; the next perhaps 30 and then after a few days maybe 1 or 2 or none. Why? We have caught them all and they are in our big pen. It’s quite a sight to see 100 little lemon sharks all schooling together in the pen. Once we are satisfied that we have all the sharks in that particular nursery area we go on to the next one.

Then we do it all over again in an adjacent location. We find only little overlap between the two nursery grounds as the situation repeats itself: 60 the first night; 30 the second and 2 or 3 the third and so on. Perhaps only 1 or 2 are recaptured from the nights before.

This summer, I will be heading back to Bimini for PIT. There will be mosquitoes, sandflies, extreme heat, sleep deprivation, and hours spent hunched over in the blazing sun fixing gillnets, but then there will also be opportunities for pictures like this:


Last time, I wasn't really able to keep up the blog while I was there because of getting only 30 minutes of internet time a week on one computer on a dial-up connection. This time it will be even worse because there just won't physically be time. So instead, what I'm going to do is post pictures and stories about when I was there before, and I'll continue that up until the point I leave for Bimini at the end of May. When I get back, I'll let you know how it went. Stay tuned...

There's more than just sharks in Bimini. In fact, there is quite a bit of interesting things on land. A week or so ago, we came upon the Bimini Boa, a snake found only in Bimini. It's not venomous, so we carried a 6-footer around for a couple of hours, taking tons of pictures. Some info about the snake is posted on the Sharklab website

Night Fishing
I often walk out onton our dock at night and look for "stuff". I've seen lemon sharks, nurse sharks, snapper, rays, jacks, needlefish, crabs, sea turtles, just to name a few, swim right up our dock. A couple of times, we've put a hydrophone in the water off the dock to see if any of the lemons swimming around are our transmittered sharks. If one is, we might hop onto a boat and track it as long as we can into the night. Other times, we just like to fish off the dock. A couple of nights ago, after learning how to make rigs for the fishing reels, some of us went out to the dock, baited the water, and threw some lines in. After about an hour, I got a bite, and I reeled in a 123cm lemon. We pulled it up to the boat, tied it up with a tail rope, and did a workup on it like we usually do. It was about midnight, and everyone was out on the dock ooohing and aaaahing, watching the workup with headlamps on. Truly nerd fun.

The Bimini Gym
I'm not sure how it happened, but somewhere along the way, me, Katie, Grant, and Sean (Sharklab staff) got a pull-up comptetion going. Apparently someone once decided that he needed to workout while he was at the lab, so he built what we call the Bimini Gym. This "gym" is a random assortment of things in the woods like a pullup bar in a tree, a climbing rope, a punching bag hanging from a tree, a barbell made with two concrete blocks on the end of a piece of rebar, and a pvc pullup bar nailed into a tree. It started out as just the four of us going out into the woods with headlamps in the middle of the night to have pullup comptetitions at the "gym", but somehow it turned into a lab-wide event. When pullup competitions weren't enough, pushups got thrown into the mix. Then wall sits. Then handstands. The fun never ends around here.

Hurricane Wilma
We've got our eye on Wilma, and it doesn't look good. We'll probably start hurricane prep tomorrow, and if it continues on its projected path, we'll probably have to evacuate to Miami later this week. Keeping our fingers crossed that it doesn't get too bad here...

Counting Down
Sadly, my time at the lab is coming to and end. Two weeks left to go, and I'm not so much looking forward to going back to reality. I've learned so much and seen so much, and it seems like time has flown. Didn't I just get here yesterday???

More random stories

1 tiger, 6 lemons, 1 nurse, 2 eagle rays, 9 southern rays - just a typical day in in Bimini.

Stuck in the Mud
Last week we had a bit of an incident in one of the skiffs. It seems we had a spring low tide, so when we went out into the middle of the lagoon, we were fine, but on the way back, we had about a foot of water. So we pushed the boat. Then about 8 inches. Then about 6 inches. Then about 4 inches. Pushing the boat across the flats is no big deal. We do it all the time when we're tracking because we follow the shark at all costs. But pushing through 4 inches of water IS a problem because the boat can't exactly float in that little water. The three of us girls on the crew pretty much carried the boat aross the sand for an hour and a half to get to a point where the boat could actually float. We moved everything to the front of the boat that we could to get the weight off the stern. EVERYTHING. We even unhooked the gas cans and moved them up into the bow. But we still had to lift the boat up in the back on the side of the battery to get it to the point where we weren't grounded. Luckily, we're all tough guys, so we made it. And in time for dinner, no less.

Stranded at the Angler
This is unshark-related, but part of the experience nonetheless...
When we go out, we go to the north island. This requires about a 25 minute walk from the Sharklab to the ferry dock, at which point we wait for the ferry to take us across. It's great, except that we have to rely on the ferry driver to bring us back. And at the end of the night, when he doesn't show up at 1am when he's supposed to, we're kind of...stranded. Luckily, there's always someone with a boat willing to take the Sharklab-ers across. Unfortunately, at 1am, the changes that that person is sober decrease dramatically. Such was the case last Saturday night, when we were lucky to make it back to land. At which point the 25 minute walk back to the lab awaited. Ah, good times.

PS - The above pic is of me and a tiger shark we caught on the longline.