Mission: Shark Longline Survey Geographical Area: Southern Atlantic/Gulf of Mexico Date: Sunday, August 7, 2011
Weather Data from the Bridge
Latitude: 34.22 N
Longitude: -077.05 W
Wind Speed: 16.38 kts
Surface Water Temperature: 28.10 C
Air Temperature: 28.90 C
Relative Humidity: 82%
Barometric Pressure: 1010.80 mb
Science and Technology Log
Last night, we finished up our last station. In total, we had 761 catches for the whole survey across a dozen different species. The sharks we caught ranged from small (less than 1 kilogram) to very large (134 kilograms). For the very small sharks, I could sometimes see the spot where the umbilical cord was attached.
Over the last few days, I learned about shark reproduction. Sharks produce “pups” (baby sharks) through three different ways. One way is the pup develops in a placenta and is nourished by the mother. It is then born live (called viviparity). A second way is an egg is produced and hatches inside the mother but there is no placental connection. The embryo eats the yoke in the yoke sac until it is completely absorbed. The pup is then born free-swimming. (called ovoviviparity). The third way is the mother lays a fertilized egg in the water and the pup is born externally (oviparity). The species we saw the most, the Atlantic sharpnose of the family Carcharhinus, produce pups through viviparity. For some species like the sandtiger shark, one of the pups will eat the other eggs inside the womb for nourishment and then just that one pup will be born. Talk about survival of the fittest!
I was able to see what a shark embryo looks like. Ian Davenport, an evolutionary biologist from Xavier University of Louisiana is studying developmental biology in female sharks. Ian is on the day shift with me and he was able to show me embryos from a pregnant female. The mother was not alive when we caught her, so we made use of the body as much as possible for scientific purposes.
This is an Atlantic sharpnose embryo. You can see the formation of eyes, snout, and tail. It is attached to a yoke sac.
You might be wondering how we can tell the difference between a male and a female shark. This is done through visual inspection. We look for the presence of “claspers” on a male shark. A clasper is a male anatomical structure. Males have two claspers. If there are no claspers, it’s a female.
This is a male shark. There are two claspers alongside the pelvic fins.
I experienced “shark burn” for the first time while handling an Atlantic Sharpnose the other day. I didn’t feel anything at first, but while I was taking measurements on its length, its tail rubbed me the wrong way. A few hours later, I noticed what felt like a stinging rash on my arm. Sharks have unique skin made of modified teeth called dermal denticles. These scales point towards the tail and help the shark swim quickly and efficiently. When you rub a shark from head to tail, it feels silky. If you rub it in the opposite direction, it feels like sandpaper. I learned this lesson the hard way!
This is shark skin magnified. These dermal denticles are sharp structures. From Google Images.
Species Seen: Tiger Shark
Atlantic Sharpnose Shark
School of Dolphin Fish
Tiger shark. You can identify this shark by the markings on its body.
My team had a great sighting of a large hammerhead recently. It was about 10 feet long. We tried to use a tagging pole from the side of the boat instead of using the cradle but the hammerhead was so strong, it broke right off the line. Even though we couldn’t collect data, it was still exciting to see such a massive shark and get an idea of its power.
Last night we finished our final station and we are heading back to port in Charleston, SC. It was really great to work with such amazing people, not only on my shift, but everyone aboard the Oregon II. I came across a variety of people with interesting careers and backgrounds. Even though the work was sometimes physically demanding, it was informative and engaging the entire time. Thanks to NOAA for giving me the opportunity to participate in the Teacher at Sea program. I learned so much that I plan on bringing back to my students! A big thanks to Mark Grace, our chief scientist, for answering many of my questions, providing feedback, and showing me how to do many tasks. I also want to thank the day team for helping me learn so much – Amy, Heather, Jim, Ian, Cliff, Jeff, Mike, and our XO Jason for giving me feedback on my blog. Thanks to Paul and Walter the amazing cooks. To the entire crew of the Oregon II – thank you! I had a great experience!