Susan Brown: Who Needs Sharks Anyway? September 13, 2017

NOAA Teacher at Sea

Susan Brown

Aboard NOAA Ship Oregon II

September 3 – 15, 2017

Mission: Snapper/Longline Shark Survey

Geographic Area of Cruise: Gulf of Mexico

Date: September 13, 2017

Science and Technology Log

We have been sampling along the coast of Florida, Alabama, Mississippi, Louisiana, and Texas at varying depths – “A” stations ( 5- 30 fathoms), “B” stations (30 -100 fathoms) and “C” stations (100 – 200 fathoms). A fathom is six feet or approximately 2 meters. The longlines are baited the same – mackerel on 100 hooks spread out across one nautical mile and then set on the bottom of the ocean. As we reel in the long line, the click and whine of the line as it’s being spooled, we wait in anticipation of what it may bring. Each station yields something different and you never know what you are going to get. Below is a list of some of the animals we have encountered.

Shark species: blacktip, sharpnose, blacknose, scalloped hammerhead, great hammerhead, bull, tiger, spinner and bonnet head (to learn more about each of these species, select it for a NOAA fact sheet).

Other animals: southern ray, cownose ray, roughtail stingray, red snapper, black drum, sharksuckers, catfish, red drum, yellowedge grouper, king snake eels and even some blue crabs.

southern stingray

catfish

So why survey sharks? Did you know that people are one of only a few species that prey on sharks — killer whales and other sharks are the others– killing over a hundred million per year?* Sharks are apex or top predators in an ocean food web and play a vital role in keeping this food web in balance. With the hunting of sharks as well as over fishing the prey that sharks eat we are disturbing the natural balance. This survey is used determine the number of sharks and other species that are present in the Atlantic Ocean including the Caribbean Sea and the Gulf of Mexico. With these numbers, the National Marine Fisheries Service (NOAA Fisheries) regulate how many sharks, swordfish and tuna can be harvested without impacting the total population. In the Pacific Ocean, NOAA fisheries work with fisheries in developing how to best manage sharks.

Apex predators in any ecosystem are vital to the health of that ecosystem. These top predators keep numbers down on the more abundant prey species and keep their numbers in check. Here is a simplified illustration of what happens when we lose apex (top) predators in an ocean ecosystem.

If the number of sharks goes down then the food the sharks eat goes up (forage fish) because they are not being eaten by the sharks. With more of those forage fish around their need for food – the zooplankton – increase. With more forage fish eating the zooplankton there are less zooplankton and their numbers begin to decrease. If there are less zooplankton then the phytoplankton numbers increase because the zooplankton aren’t around the eat them. Removing top predators from any ecosystem can have an impact on the entire food web and this phenomena is called a trophic cascade.

Personal Log

When people think of sharks, they think of the movie Jaws. Unfortunately this has given sharks a bad reputation and has vilified these animals that are essential to the ocean food webs. Sure, there have been shark attacks, but did you know that more people are killed each year by electrocution by Christmas tree lights than by shark attacks? When people imagine sharks, they think of enormous sharks that eat everything in sight. The reality is that sharks come in all sizes and shapes. A mature Atlantic sharpnose shark will only get to be 3.5 feet long with the world’s smallest shark being the dwarf lantern shark that can fit in the palm of your hand. The largest shark is the harmless-to-human whale sharks that feeds primarily on plankton and can grow up to 60 feet!