NOAA Teacher at Sea
Emily Sprowls
Aboard NOAA Ship Oregon II
March 20 – April 3, 2017
Mission: Experimental Longline Survey
Geographic Area of Cruise: Gulf of Mexico
Date: March 31, 2017
Weather Data from the Bridge
12:00 hours
29°36.7’ N, 87°43.7’ W
Visibility 10 nm,
Wind 6 kts 350°N
Sea wave height 2-3 ft.
Seawater temp 22.9°C
Science and Technology Log
On the deep longlines we sampled many gulper sharks (Centrophorus spp.). Gulper sharks have cool anatomical adaptations, including their huge reflective eyes, buccal folds for gulping their food, and the ability to excrete huge amounts of slime from their skin. Gulpers also have very large eggs, which is of particular interest to my crewmate Lydia Crawford, a scientist from Tulane University that is studying shark reproduction and evolution.
Lydia is collecting eggs from as many different kinds of sharks as she can in order to understand more about how sharks evolved a variety of reproductive strategies. Oviparous sharks and skates lay egg cases, also knows as “mermaids purses.” Oviviparous sharks let their eggs hatch internally and the babies are born swimming. Some embryos eat other eggs or even their siblings as they develop in their mother! Placental viviparous sharks are also born alive, but the embryos are fed via umbilical cords, similar to us humans.
Lydia will examine the microscopic structures of the shark ovaries she collected when she gets back to her lab. She hypothesizes that certain features of the ovaries have allowed sharks to evolve the ability to give birth to large babies, ready to act like the apex predators they are!
Personal Log
Last night we caught a blacktip shark (Carcharhinus limbatus) that my data sheet says measured 1.4 meters, but my memory says it was MUCH BIGGER because he lunged and snapped at us! Most of the sharks we have collected have been rather stunned by their brief trip out of the ocean onto the deck, but this guy acted like a shark still in the water! He and his biting jaws were clear reminders of what incredible predators sharks are. He put a healthy dose of fear back in me, along with a lot of respect for the science team who managed to measure him despite his aggressive activity!
Kids’ Questions
- Why don’t sharks have swim bladders?
Sharks maintain neutral buoyancy by having very large, oily livers. We confirmed this by throwing the dissected lobes of the liver overboard and they floated!
- Is there a shark that glows in the dark?
The eyes of some of the deep sea sharks that what we caught appear to be glowing because they are so big and have very reflective layers (called tapeta lucida) that shines back the boat lights. However some sharks, including the lantern shark, have special organs called photophores that glow!
- How would you recommend reversing the sense of fear people associate with sharks?
Lydia’s response:
As a scientist, you shouldn’t try to reverse people’s fears because you can’t rationalize away a feeling. Also, we should have a respectful fear of sharks. They are amazing predators! Instead we should convince people why sharks are important in the ocean ecosystem as keystone species.