Welcome to the second guest post in Larisa Bennett’s series about her semester at UNC’s Institute of Marine Sciences (IMS) through the Institute for the Environment Field Site program! Today, Larisa takes us out to sea for a shark research expedition. For more of Larisa’s aquatic adventures, check out her first post!
Shark attacks along the North Carolina coast captured a lot of press this summer. It is little wonder that most people would scramble to get as far away from a real live shark as possible. Not the IMS students onboard the R/V Capricorn, as we headed out at sunrise towards Shackleford Banks where we hoped some shivers of Selachimorpha were swimming that morning.
Fun Facts: A group of sharks is called a herd, pod, school, gam, grind, collage, or shiver. Selachimorpha is the scientific classification for the modern shark we know today. Shark attacks are statistically extremely rare because truth is most sharks have no interest whatsoever in biting a human. We are not their natural prey and they pretty much bite things they want to eat.
A hum of excitement vibrated on deck this particular morning as we all wanted to have a close encounter of the personal kind with as many sharks as we could. Marine scientists see sharks not as the scary man-eating monster depicted in Jaws, but as fascinating, ancient survivors that have existed for millennia. The earliest known sharks were swimming in Earth’s oceans more than 420 million years ago. Modern sharks’ ancestry dates back to around 100 million years ago which is still much, much older than human ancestry. In our way shorter history in the great evolutionary timeline, humans have killed sharks in much greater numbers than they attack us, usually to get their fins to make shark fin soup. As apex predators, sharks are at the top of the marine ecosystem food web, but that’s because the ocean is not the natural habitat of humans. Under the “C,” sharks rule! I just wanted to get to touch one of these beautiful deep sea bosses.
Marine biologists have been tagging sharks in the waters off Shackleford Banks for over 40 years. The project was begun in 1972 by IMS marine scientist Dr. Frank J. Schwartz and is the longest ongoing shark survey nationally. Marine biologist Dr. Steve Fegley, an IMS professor, is part of a team carrying on the work of amassing the longest-running shark database in the country. On each shark tagging trip out from our Morehead City dock, the first step in catching sharks is to get the bait. Once out from shore the R/V Capricorn dropped a trawl net into the water. Trawl nets drag along the ocean bottom behind the boat scraping up everything in their path into a bag at the end of the net.
When we had dragged the trawl for a little bit it was pulled up and emptied out onto the deck of the boat. Dr. Fegley showed us some of the cool sea creatures captured in the net including butterfly rays, lizardfish, stone crabs, spiny urchins, squid and shrimp. The shrimp were separated out to be cooked for lunch as they wouldn’t have survived back in the sea after being captured, while other animals that would live such as the butterfly rays were carefully freed from the trawl net and released. Most of the fish however were put out as bait on long stretches of fishing line to catch sharks.
Once the hooks were baited, we began to feed the longline out across the water. We attached buoys so the line floated on the water surface while the baited hooks were suspended at depths where sharks would be likely to bite. An hour later we reeled the line back in to see what had been caught. We pulled in two sharks on the first line. Both were Atlantic sharpnose (Rhizoprionodon terraenovae) sharks, one of the smaller shark species. They were measured and tagged before being released back into the water.
Tagging is similar to a human getting a vaccination. The tag is stuck down in a metal tube with a small sharp pointy end. The tube is inserted into the meaty muscle by the shark’s dorsal fin (the fin on top of its body) until the tag is in. The tube is then pulled back out, leaving the shark unharmed. The tag is a tiny, bright yellow, tubular plastic stick that protrudes slightly out of the skin next to the fin so it is easily seen. It lists the IMS contact information so that if that shark is caught later, the fisherman can call it in. After our first two sharks were measured, tagged, and sent on their way, we took the boat to another site further offshore and redeployed the longline with fresh bait on the hooks.
The second longline brought in six Atlantic sharpnose. Everyone got to tag and release sharks. I got to touch them!! Their brownish gray skin feels silky smooth and with their long, pointy snouts, sharp teeth, jutting lower jaw and round staring eyes, they really are quite adorable looking. Atlantic sharpnoses are one of the smaller species of sharks reaching a maximum length of 110 cm or about 3.5 feet long. Most people typically think of sharks like the Hammerhead (Sphyrna mokarran), Great White (Carcharodon carcharias), or Tiger (Galeocerdo cuvier) sharks. These larger sharks, called the “great sharks,” are the top dogs of the oceanic food chain. All sharks from small to intermediate size to the great sharks play a crucial part in maintaining a healthy marine ecosystem. Their role is to cull the populations of fishes and other marine organisms below them on the food chain. Great sharks as apex predators prey on Atlantic sharpnose among other marine inhabitants such as large fish, cownose rays and turtles, removing the older and weaker animals in those populations. In turn, Atlantic sharpnose, as mesopredators, feed on a variety of small fish, shrimps, lobsters, crabs, and mollusks such as clams, oysters, scallops, snails, slugs, and squid.
The IMS shark tagging survey data demonstrates that there has been a large decline in the amount of great sharks in this area. The smaller sharks such as the Atlantic sharpnose are now the most frequent catch for the taggers. This effect mirrors the global trend of declining numbers of great sharks. We unfortunately (although not really surprisingly) did not see any great sharks. But at least we had the adorable Atlantic sharpnose to hang out with. I finally got to touch sharks!