The past 2 days we spent at the Berry Islands – a small, relatively uninhabited patch of islands in the Bahamas. The water here looked like a patchwork of aqua blue and emerald green stained glass. You could see straight down to the bottom. In the distance, the ocean just seemed to melt into the sky. The berries have lots of nooks and crannies, lined with mazes of mangroves that open up into shallow lagoons – perfect habitat for juvenile sharks.
The mangroves were teeming with wildlife: ibis and osprey flying overhead, manta rays and sting rays gliding through the water, little bait fish schooling beneath us, bigger fish like grouper and barracuda trolling the mangrove edges looking for a meal, and heaps of sea turtles darting back and fourth through the canals. The mangroves are quite the hangout place and lots of different animals use them as nursery grounds, including lemon sharks.
We caught and tagged three lemon sharks on Wednesday. We would have had four but one snapped the line. I caught a newborn lemon, it was around 2 feet long and only about one month old! In contrast, Mark caught one of the biggest lemons of the day – over 5 feet, and probably a few years old. As you can imagine, the smaller sharks are much easier to handle, but you still have to be really careful.
When working with sharks, you don’t just have to worry about getting bit, but also getting smacked by the tail (which packs a punch). And, if the shark’s skin scrapes against you fast in the wrong direction, you’ll end up with rug burn. A shark’s “skin” is made up rows of microscopic tooth like scales that lay flat against its body. If you move your hand from the tip of the nose to the tail, it feels smooth and leathery, but if you move your hand back the other way, it pushes up against the scales and feels like sandpaper.
To make the shark more comfortable while the team is taking their measurements, Mark gently turns the shark on its back with its white belly exposed to the sky. This puts the shark in a meditative state called “tonic.” It also makes it easier for us to work with the shark.
The DNA samples we take from the sharks are being analyzed by Kevin Feldheim, from the Pritzker Lab at the Chicago Field Museum. Kevin was on the first leg of this trip on Grand Bahama Island. So far, members of the team have shown that, although all the same species, there are genetically independent populations of sharks on different islands in the Bahamas. They have seen genetic differences in species as little as 150 km apart (about 93 miles or the distance from New York City to Philadelphia). This means there is surprisingly small-scale genetic structure in lemon sharks, a finding that is unprecedented in shark research. This also means you have to manage sharks on a fine scale. The more places/samples we get – the better the resolution of this genetic diversity.