Mission: Shark Longline Survey
Geographical Area: Southern Atlantic/Gulf of Mexico
Date: Sunday, July 31, 2011
Weather Data from the Bridge
Latitude: 30.39 N
Longitude: -080.41 W
Wind Speed: 13.67 kts
Surface Water Temperature: 29.50 C
Air Temperature: 29.10 C
Relative Humidity: 78 %
Barometric Pressure: 1016.43 mb
Water Depth: 37.10 m
Science and Technology Log
A part of any good experiment or survey is the careful collection of data. We know that without a good data collection plan, our results may have error or be open to wide interpretation. The shark longline survey has been going on for the past 17 years in order to understand the abundance of shark species in this area. It has standard procedures and protocols that we must follow so that each survey is consistent. Hmm…that sounds similar to what we do in science class!
Every time we reach a “station” (a pre-designated spot) our team collects data on the characteristics of that area. One piece of technology we use to do this is called a CTD (which stands for conductivity, temperature, and depth). This instrument is placed overboard with the help of a winch and takes measurements for several minutes. Conductivity tells us information about the salinity (amount of salt) of the water. The device also reads the temperature, depth, levels of chlorophyll, dissolved oxygen, and can give us water samples. This is important because every time we change stations, we want to know about the conditions of that area. The data from the CTD is then sent electronically to a data room and graphed.
We also collect data on the color of the ocean water, the wave height, and the percentage of cloud cover. This last one is a bit tricky because it is so subjective.
It is also important to collect data consistently. There are two shifts aboard the boat – the day shift (which I am on) and the night shift. Each shift is 12 hours long. We collect data even in the middle of the night. What do you think would happen if we only collected data on sharks during the day time?
There are several measurement tools we use. The measuring board allows us to place a small shark on the board and read its length in millimeters. We take two readings – one for the length from the snout to the fork where the tail splits, the other for the entire length of the shark from end to end. The spring scale is used to measure the shark’s weight in kilograms. If the shark is too big for either of the above tools, we will take measurements in the cradle. We use a flexible tape measure for length, and record weight through a scale on the cradle. We know the cradle’s weight, so all we have to do is record the total weight of the cradle with the shark in it and subtract (see kids, math in the real world!)
I mentioned earlier that we have satellite TV access on the boat. Actually there are three – one in the lounge and two in the galley. Funny enough, we have the perfect program to watch this week on the Discovery channel…happy Shark Week everyone! Yesterday, we had to postpone doing our longline survey at one station due to a distress call from a small boat that was 10 miles away.
Species Seen Today
Atlantic Sharpnose Shark