Steven Frantz: Sharks at Sea, August 3, 2012

NOAA Teacher at Sea
Steven Frantz
Onboard NOAA Ship Oregon II
July 27 – August 8, 2012

Mission: Longline Shark Survey
Geographic area of cruise: Gulf of Mexico and Atlantic off the coast of Florida
Date: August 3, 2012

Weather Data From the Bridge:
Air Temperature (degrees C): 28.79
Wind Speed (knots): 14.14
Wind Direction (degree): 199.05
Relative Humidity (percent): 070
Barometric Pressure (millibars): 1017.95
Water Depth (meters): 58.0
Salinity (PSU): 35.635

Location Data:
Latitude: 3409.72N
Longitude: 17611.11W

SHARKS AT SEA

Our 300^th mission aboard the Oregon II is a Longline Shark Survey.  Stratified randomly selected sites have been generated using Arc GIS Software. This eliminates potential bias in sampling and each area has an equal opportunity to be sampled. Two depth strata zones (A: 5-30 fathoms, B: 30-100 fathoms) have been factored for the Atlantic. In order to avoid all sampling sites randomly bunched all together, the area has been divided into 60 nautical mile geographic zones from southern Florida to North Carolina. 60% of our effort (ex. time at sea) is put toward “A” stations and 40% of our effort is put toward “B” stations. This method of picking stations is called proportional allocation.

We are here to find sharks. This is important because so very little is known about them, or many of the other animals living in an extreme environment (extreme for people to live in).

One if the first sharks we caught was a blacknose shark, Carcharhinus acronotus. It is relatively small, a uniform gray color, and has a black tip on its nose.

The most common shark found so far has been the sharpnose shark, Rhizoprionodon terraenovae. Both sharpnose and blacknose sharks are considered to be small coastal sharks by the National Marine Fisheries Service. While similar in size to the black nose shark, the sharpnose shark is spotted. When brought on board, their size is nothing compared to their strength. I guess you have to act tough when you’re little!

Tough though they may be, we caught several sharp-nose sharks that have become bait themselves! I wonder what (kind of shark?) it was that ate the back half of this sharp-nose?

One of the many data we are collecting is the sex of the sharks. Pictured below are a male (top), then female (bottom). The male shark has claspers, which are used for internal fertilization. Claspers are also used to determine a male’s age depending on how calcified they are.  This is the standard way to determine sex on all the sharks we have caught thus far.

Another piece of data collected is a clip of flesh from a fin. This is a non-lethal way for scientists to obtain DNA for genetics studies and possibly for use in population structure for identification purposes.

As we saw above, some sharks don’t make it on board alive. While this is uncommon, the opportunity does present itself for more invasive study not done on living animals. Sharpnose sharks give birth to live young (viviparous). Pictured below are young sharks taken from a female. It is interesting to note that whether the shark is male or female can be determined at this early stage. Remember, not all sharks reproduce this way.

Sandbar sharks, Carcharhinus plumbeus, have been the next most common sharks caught. These are quite a bit larger than sharp-nose sharks, averaging 150 centimeters long and 35 kilograms in mass.

We must be safe when collecting data. Shark’s skin is like sandpaper, so if the teeth or tail doesn’t get you, you can also be given a pretty red rash by the scrapping of their skin against your skin.

Sandbar sharks were popular with the shark fin soup industry because they have a very large dorsal fin compared to their body size. Sharks were caught, their fin was cut off, and then the still-living shark was released back into the ocean to die. This practice has been outlawed in U.S. waters.

Watch the video below as a sandbar shark is caught and brought to the Oregon II.

The prettiest shark (at least to me) I’ve seen so far is the tiger shark, Galeocerdo cuvier. They can get very large. Three meters long or more! The ones we’ve found have been smaller. The one I’m holding is very young. The umbilical scar was still visible! Tiger shark teeth are different from most sharks in that a tiger shark’s teeth are made to slice their prey, like the shells of sea turtles.

Sharks don’t have eyelids, like we have eyelids, to protect their eyes. They have what is called a nictitating membrane to protect their eyes. Here is a picture of the nictitating membrane partially covering a sharpnose shark’s eye.

The most unusual shark we’ve caught has been the scalloped hammerhead shark, Sphyrna lewini. Once on board the Oregon II they seemed to be docile (for a shark), however, their eyes on the far ends of their head were always looking, watching what was going on.

Why is their head shaped like it is? Even scientists don’t know for sure. Some think it acts as a hydrofoil to help it move through the water. Other scientists think (because of its large size) it helps detect electrical impulses in the water (like a sixth sense). Do you have any ideas why their head is shaped the way it is?

I have been working the day shift: from noon to midnight. The other crew is the night shift. In addition to what we have seen so far, the night shift has also seen a great hammerhead, Sphyrna mokarran and a silky shark, Carcharhinus falciformes.

We still have five days of fishing left. What will we catch next? I’ll let you know!