Mission: Shark Longline Survey
Geographical Area: Southern Atlantic/Gulf of Mexico
Date: August 16, 2011
Weather Data from the Bridge
Latitude: 25.15 N
Longitude: 82.48 W
Wind Speed: 2.09 kts
Surface Water Temperature: 29.20 C
Air Temperature: 30.10 C
Relative Humidity: 69.00%
Science and Technology Log
If there’s one thing I’ve learned since I’ve been on this trip it is that both science and technology are crucial for doing a shark survey. Keep in mind NOAA Ship Oregon II’s mission is not to fish for sharks, rather it is to survey them. In other words, it is to find out how the sharks are doing and where they like to hang out in the ocean. Thus, the ship doesn’t ONLY go to the “shark hot spots” so to speak. Instead, there are various locations the ship stops at to perform a survey. These are called stations. The stations vary greatly in depth, temperature, dissolved oxygen, etc. It would be similar to marketers taking a survey to see what restaurants people prefer.
With that being said, there is a certain science to performing a survey of the sharks. Here is how it is done. There is much preparation before leaving port to do a survey. NOAA Ship Oregon II cannot leave port without Atlantic mackerel, and lots of it. This is the bait that is used to catch the sharks. The hook of choice is a circle hook. The fishing line is monofilament and extremely strong. These are the basic items needed, but there are numerous other tools needed such as the cradle for larger sharks, tagging tools, vials for samples, and the list goes on. Suffice it to say, once the ship leaves from port, everything has to be on board in order to have a productive survey.
Anyone who fishes knows there are numerous ways to catch a fish. So how do you catch a shark? If you’ve ever seen the movie, “The Perfect Storm,” then you have a good idea. The method used is called longlining. As the name claims, this method makes use of a long line. The line must first be prepared. In order to do this the circle hooks are baited with Atlantic mackerel. There are 100 hooks in total to put on the line. The hooks are part of a unit called a gangion. A gangion consists of a leader, a monofilament line, and a circle hook. These are placed in a barrel. There are 50 gangions with bait per barrel, for a total of 2 barrels per fishing set.
Incidentally, there are 2 shifts: day shift (noon until midnight) and night shift (midnight until noon). I am on the day shift. Thus there are stations being worked 24 hours a day. The bridge will announce when we are coming on another station. Also, it is posted on the dry lab door so we can all be prepared for the next station. Knowing this, the shift gets the mackerel ready by thawing it out, then cutting it up to bait the
Once the ship is to the station, everyone gets in their places, and the OOD (Officer of the Deck) disconnects the engine. At this point the drift test begins. This takes into account both the wind and the current to determine what direction to set the line. If there is too much current, determined by the Field Party Chief and the OOD, the station is either canceled or moved closer to shore. Next the ship slowly moves forward (4 knots) and the line is fed from the ship. The line, which is 1 nautical mile, is let out at the stern (back) of the ship. The fishermen are responsible for feeding it through blocks (pulley) system. The 1st thing on the line is a high flyer. This is an orange flotation device put at the end of the line.
The next thing put on the line is a weight. This sinks the line to the bottom. At this point, the first of 50 baited gangions are handed to the fishermen to clip to the line, each being evenly distributed. It should be noted that each gangion has a hook number so that an accurate record can be kept. The hook numbers are taken off a line and clipped on the gangion as the bait is being fed over the deck to the fisherman. After the 50th gangion, another weight is put on the line, followed by 50 more gangions, another weight, and lastly, a high flyer. While all of this is going on, one person on the team records data on the computer which is instantly uploaded with such things as the latitude and longitude and real time of when each hook is deployed.
The longline is allowed to soak for 1 hour before it is brought back on board on the starboard (right) side of the well-deck, just aft of the bow (front). During this time the deck and buckets are cleaned up and the CTD is deployed (Conductivity Temperature Depth).
The CTD takes many measurements including temperature, salinity, turbidity, chlorophyll, depth, and dissolved oxygen. These measurements give the scientists valuable information for the habitats of the sharks. For example, any level of dissolved oxygen 2.0 mg/liter or lower is considered apoxic and causes physiological stress on an animal. Most animals live in an area between 2-7 mg/liter of dissolved oxygen. A reading of 7 would only be found in very cold water such as the Arctic.
In addition to the CTD readings, the scientists report the water color along with the current weather conditions.
After the line has soaked, the team meets at the bow to haul in the line. The fishermen unclip the gangions from the line and hand it off to a scientist who records the hook number and the condition of the bait. If a fish is caught, it is brought aboard and morphometric (total length, fork length, sex, and weight) data is collected.
In the event a larger fish is caught, it is placed in the cradle.What are the benefits of doing a longline survey? It gives the scientists presence/absence data from looking at what was caught and was not caught. It gets samples from the Gulf to compare with other areas.
One word: WOW! Let me say it backwards: WOW!!! This week is DEFINITELY making my “Top Ten Life Experiences” list!! Shark Week has absolutely nothing on this NOAA crew! It is evident they eat, sleep, and live sharks and other fish all year long. NOAA Ship Oregon II needs to have a camera follow them for a reality show called “Shark Year.” If they aren’t catching it, they are studying about it. I am amazed at the depth of knowledge of the entire crew, including each and every member on board, of the ocean. What impresses me even more is their enthusiasm and patience in teaching this teacher how it all works.
Now for your questions. . .
One of you asked about shark finning. According to the scientists and fishermen on board it is not a big problem off the coast of the United States like it is in Asia. Here it is regulated. In fact, when commercial fishermen bring in their sharks, the fins have to be attached, so that cuts down on this practice.
Another question that came up was in regards to tagging. On this ship the scientists mainly use passive tagging techniques. This requires the fish to be recaptured after it has been tagged. The tag has a phone number to call when the shark is caught as well as an identification number. Another method of tagging is active tagging, for instance satellite tags. Satellite tags are attached to animals to study migration. These are very expensive, ranging from $3,000-$5,000. They are set to pop off the animal at a predetermined time and date and transmit data to a satellite in order to plot the shark’s course. Many shark species are migratory so this type of tag is beneficial to see their migration patterns.
Also, a question was asked about how deep it needs to be to safely navigate. According to Cap, the draft for the ship is 15 feet. The ship can safely sail in 30 feet of water. That’s unbelievable for a ship of this size, huh? It makes Orgeon II a great vessel to do the shallow water surveys. Most other ships can’t go that shallow.
By the way, great job class on last blog’s poll! The correct answer was 70! You all aced the quiz!
I also have to share a picture of my son, Hayden. His 1st day of school was Monday. I can’t believe he is already in 6th grade! Hayden is a shark enthusiast and is following my blog at home with my parents. Cap has already told me he is welcome on the ship. Someday he can come study sharks, just like his Mom!
Shark Gallery Pictures
The next blog will be a lesson on specific sharks, but for now, enjoy the pictures!!