Tag: oviparity

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Kathleen Gibson, Wild Weather, August 2, 2015

NOAA Teacher at Sea
Kathleen Gibson
Aboard NOAA Ship Oregon II
July 25 – August 8, 2015

Photo taken from the highest point on the ship.
A Nurse Shark in the cradle
Photo taken from the highest point on the ship.

Mission: Shark Longline Survey
Geographic Area of the Cruise: Atlantic Ocean off the Florida and Carolina Coast
Date: Aug 2, 2015

Coordinates:
LAT   3428.300 N
LONG  07705.870 W 

Weather Data from the Bridge:
Wind speed (knots): 11.2
Sea Temp (deg C): 29.1
Air Temp (deg C):  25.7

Science and Technology Log: Shark Reproductive Strategies

Rough Seas and bad weather have delayed our sampling.  I’m getting use to walking sideways.

Bringing in gangions in the rain.
Bringing in gangions in the rain.

Today we reached the northernmost sampling station of our cruise, just off the North Carolina coast. The latest stations have been further off shore than those previous and we’ve caught fewer sharks. However, the sharks we have caught have been much larger. Our catch included Sandbar Sharks, Scalloped Hammerhead, Spinner, Nurse and Black Nose.

Sharks have a number of reproductive strategies ranging from egg laying to placental formation. Oviparous sharks produce and release egg cases made of a collagen (protein). The case surrounds the developing embryo and a large yolk with the vital nutrients required for shark development. This is called lecithotrophic (all nutrients from yolk). Oviparous sharks can take to 2 years to develop within the egg case.

Cat shark adult (Image courtesy of Ian Davenport)
Adult cat shark
(Image courtesy of Ian Davenport)
Cat Shark egg case. Photo Courtesy of Ian Davenport
Cat shark egg case. Photo Courtesy of Ian Davenport

Sharks that give birth to live young are considered Viviparous. Within this category there are two major types. Those that produce eggs with large yolks with all required nutrients, but remain in the uterus for gestation, are called yolk-sac vivipores (ovoviviparous, or aplacental viviparity). In some cases, offspring will consume other eggs (oophagy) in the uterus to gain additional nutrients. An advantage to this type of reproduction is that the young sharks are larger when they are born and have a higher survival rate.

Yolk-sac embryos (Image courtesy of Ian Davenport, Ph.D.)
Yolk-sac embryos (Image courtesy of Ian Davenport, Ph.D.) 

The last group, considered to be the most advanced, is the Placental Group. As with the other types, a yolk is produced that can initially provide some nutrients to the developing pup. However, in the uterus the yolk sac after it is depleted is modified into a placenta through which nutrients can pass from parent to offspring. While fewer offspring are produced at one time, they are typically more robust and have a higher survival rate. Most of the sharks we have caught on this cruise are placental vivipores.    

Placental Shark (Image courtesy of Ian Davenport)
Placental Shark
(Image courtesy of Ian Davenport)

Career Spotlight: Dr. Ian Davenport, Ph.D., Research Scientist

Dr. Ian Davenport, Ph.D., is a Developmental Biologist at Xavier University, New Orleans, and has been a volunteer on this cruise for 7 years.

Dr. Ian Davenport dissecting a female Sharpnose shark.
Dr. Ian Davenport dissecting a female Sharpnose shark.

Ian hails from Manchester, England, and his path to becoming a scientist was quite unusual. Similar to others on board, he always had an interest in Marine Science, and sharks in particular, but school was not a priority early on. He spent time travelling and learned a trade as well. He finally decided to return to school, but being accepted was a challenge. Fortunately Ian’s academic ability was recognized and he was accepted to the University of Newcastle upon Tyne where he studied Marine Biology, but a course in Developmental Biology particularly resonated. He went on to earn his Ph.D. in shark developmental biology at Clemson University.

Ian’s research focus is in evolution of “live bearing.”  As noted above, shark species employ a number of reproductive strategies. Placentals are considered to be the most advanced. Ian is studying the eggs of placental sharks and the structure of the cells that surround the egg. His research has revealed some interesting cell features that may aid in nutrient delivery to the developing embryo. If a female shark is caught during the cruise and does not survive, Ian collects the eggs for later study.

Career Spotlight: Chuck Godwin, Deck Crew and Environmental Compliance officer

Chuck has a B.A. in History and has also studied Wildlife Management. Chuck spent 10 years in the Coast Guard and left in 2000, but he was recalled to active service on two occasions – after 9/11 and after Hurricane Katrina. In addition to his work as part of the deck crew, where he is involved in all deck operations, Chuck is also the Environmental Compliance Officer. As such, he manages hazardous waste compliance.

Chuck Godwin hauling in the Longline.
Chuck Godwin hauling in the Longline.

It’s apparent that Chuck enjoys his work. He is all business when he needs to be, but has a knack for adding a note of levity when appropriate. He keeps me laughing, even when the fish aren’t biting. Chuck notes that as a member of the Coast Guard, part of his job was to enforce U.S. fisheries laws. With NOAA he plays an important role in establishing those regulations and this makes the work that much more rewarding.

Personal Log

The weather has been poor since yesterday. Lightning caused a five-hour delay in setting the longline in the night; the ship traversed back and forth over the sampling area waiting for the worst of the storm to pass. Sleeping was a challenge – I think some of us were airborne a few times. Thank goodness for the patch and a few saltine crackers. I took the video below in my bunk as I was nodding off to sleep.

Today’s rough seas and high winds prevented us from using the cradle to bring sharks up to deck height. Ken’s dual laser device, mentioned in my last blog post, was put to good use to estimate the size of the large sharks before they were released.

I need to give shout out to the ship’s cook Walter Coghlan and the second cook O.C. (Otha) Hill. The food has been great and plentiful. ( Homemade Mac n’ Cheese – need I say more?)  Walter takes special care to set aside a plate for us if we are on duty during mealtime. The ice cream sandwiches are much appreciated too.

In the kitchen with Walter.
In the kitchen with Walter.

New species seen since last posting: Sharksucker (a type of Remora, Echeneis naucrates), Blacktip (Carcharhinus limbatus) 

Trying to get a Remora to stick to my arm. What a strange feeling. (Photo: Kristin Hannan)
Trying to get a Remora to stick to my arm. What a strange feeling. (Photo: Kristin Hanna
The view from the Bridge
The view from the bridge.

  

Still working on the hooks. (Photo: Ken Wilkinson)
Still working on the hooks. (Photo: Ken Wilkinson)

Check out these interesting shark facts.

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Maureen Anderson: Homeward Bound, August 7, 2011 (Post # 6)

 NOAA Teacher at Sea
Maureen Anderson
Aboard NOAA Ship Oregon II (NOAA Ship Tracker)
July 25 — August 9, 2011

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.

atlantic sharpnose embryo
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.

male with claspers
This is a male shark. There are two claspers alongside the pelvic fins.

female sharpnose

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!

dermal denticles magnified
This is shark skin magnified. These dermal denticles are sharp structures. From Google Images.

Species Seen:
Tiger Shark
Sandbar Shark
Atlantic Sharpnose Shark
Red Grouper
School of Dolphin Fish

tiger shark
Tiger shark. You can identify this shark by the markings on its body.

Personal Log

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!

sunset
Sunset from the stern.