Kathleen Brown: This Week at Sea! June 12-14, 2011

NOAA Teacher at Sea
Kathleen Brown
Aboard R/V Hugh R. Sharp
June 7 – 18, 2011

Mission: Sea Scallop Survey
Geographical area of cruise: North Atlantic
Dates: June 12-14, 2011

June 14, 2011

Weather Data from the Bridge
Time: 3:32 PM
Winds 13.0 KTs
Air Temperature: 10.78 degrees C
Latitude 41 40.26N Longitude 068 19.96W

Science and Technology Log

Basket of Scallops
Basket of Scallops

Today I have been thinking about sampling. On this leg of the Scallop Survey, we may dredge up to 150 times. Each dredge is called a station. The stations on the trip are generally selected at random, from the places along the bottom of the ocean that scientists expect to find scallops. Once in a while we stop at a non-random station. This is a location that scientists have been studying for a number of years. By selecting the same location over and over again, scientists can see how the scallop population is changing. One scientist uses the data collected at the non-random stations to age the scallops. Scallop shells have rings that scientists can count to see how old the scallop is. (This is similar to the way that a scientist might tell the age of a tree.)

Every time the net is hauled onto the table, we sort every item that has been pulled up from the ocean. Of course sea scallops are the species that are being studied, but we count all the fish as well. The scallops are placed in orange baskets, similar in size and shape to a round laundry basket. Once a basket is filled to the top, we grab another basket. On some tows, there are no sea scallops. On tows where scallops are abundant, there have been as many as 30 baskets full of scallops. If we have collected a few baskets of scallops, we will measure the length of each animal. However, imagine trying to measure and count every scallop in thirty baskets. (My fellow scientist Aaron and I have found that we typically measure 250-300 scallops per basket.) It would not be practical, especially in locations where stations are close to each other. There just wouldn’t be enough time. In those cases, the Crew Chief will select, randomly, the baskets that will be sorted and measured. Usually, it is one fourth of the total sea scallop catch. This is called a sub-sample. Scientists can use the data to extrapolate (estimate) the size and character of the catch.

Smaple a scallop
Sampling a scallop

Scallops that come up from the tows vary in ways other than in size and age. Some of the oldest sea scallops that have been dredged up have been covered with small ecosystems. Barnacles, sea sponges, and algae are firmly attached to the shell. Many of the sea scallops have been so crusted that we had to remove the colonies of barnacles before we could measure them.

We have not been able to see any stars at night, as it has been overcast the whole trip. I had hoped to see a brilliant night sky. Last night I was able to count three other vessels out on the water – small lights bobbing off in the distance.

Personal Log

The day crew has developed a great bond. We have fun joking and telling stories. Before we head out on deck, we each guess the number of species that we might see in the tow. The friendly competition makes us laugh. In the galley, there is a satellite television. If the ship is traveling in a certain direction, we can receive a signal. Can you imagine being 200 miles out in the ocean and watching the Boston Bruins and the Vancouver Canucks play in the Stanley Cup finals? Go Boston!

Question of the Day

In areas where American sea scallops are abundant, what other marine animals would scientists expect to find?

 

June 12, 2011

Weather Data from the Bridge
Time: 12:50 PM
Winds 18.7 KTs
Air Temperature: 11.33 degrees C
Latitude 41 18.20N
Longitude 066 49.56W

Science and Technology Log

The Chief Scientist, Kevin, shared some information with me this morning that helps to put our work into perspective. NOAA conducts an annual sea scallop survey, which covers an area from Cape Hatteras to Georges Bank. I am traveling on the second leg of the 2011 survey. Over time scientists and fisherman use the data to track the distribution of the sea scallops. The scallop catch is reported in numbers and disaggregated (broken down) by the size of the animals. Catches are categorized by the size of the scallops’ shell height: less than or equal to 90 mm, greater than 90 mm, and greater than or equal to 100mm. (Notice how scientists use the metric system of measurement to report their results.)

To be sure that the information being compared is valid, scientists use the same type of equipment and the same procedure on every tow and on every trip. According to Kevin, fifteen-minute tows are made at the speed of 3.8 KTs. That means that the dredge is pulled behind the boat for the same time and at the same speed. The dredge (think big, square fishing net) is called a modified 8-foot New Bedford type scallop dredge and it travels along the bottom of the ocean floor to get the sample. It is made of chains linked together and has a liner made out of nylon rope that helps to keep the small scallops in the dredge. Nate, the Crew Chief on my watch, and Sam, a graduate student studying scallops, share with me their experiences on a commercial scallop boat. Those vessels typically have two dredges, each one approximately fifteen feet wide. Imagine the numbers of scallops those ships can catch!

On selected tows, random scallops are studied. On one tow, Aaron and I work together to sample five scallops. First we scrub the outside of the scallop really well, using a wire brush. When we measure and weigh the scallop, we will work to get as accurate a result as possible. Once we have collected data on the exterior of the scallop, I cut it open. Immediately we can tell if the scallop is a male or a female. If the scallop is a male, the gonad is white. If a scallop is a female, the gonad is red. We weigh the gonad and then we weigh the “meat.” The meat is the part of the scallop that most people eat. It is the muscle of the animal. Finally, we save the shells for the scientist back on land who has requested the data.

I have been taking lots of photographs of everything that we have been studying on the cruise. I will upload them when I return to land because of the limited Internet connection on the ship.

Personal Log

I have been sleeping really well on this ship. It doesn’t take very long, once I get to my cabin and climb into my bunk, for me to fall asleep. Working twelve hours in the salt air can make a body tired! Once in awhile, the ship will rock back and forth in a way that wakes me up. I look at my wristwatch and return to sleep. What a great feeling to wake up rested in the morning.

Question of the Day
What does by-catch mean? Why is it important that scientists measure the number and size of the by-catch in each tow?

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