25 October, 2003
The good news is that the seal-weighing sled is now fully functional. The bad news is that we now have a full-service weighing station that is accurate to within a few grams, parked immediately outside our door. It might make us think twice about grabbing that extra Oreo off the plate in our quest for caloric gratification!
Darren spent a day in McMurdo unraveling the mystery of the weighing sled. The problem turned out to be strictly mechanical. The four load sensors, fixed under the corners of the weighing platform, are contained within welded metal brackets. While they were fully functional at 72F when the sled was tested in the United States, they didn't work properly after a night spent in the cold of Antarctica. Why? Well, metal contracts when it cools-the brackets became too tight and didn't allow the sensors to move within their housing. Once He determined that this was the problem, it was a matter of grinding the brackets down a bit to ensure that the sensors could move freely even after the metal contracted in the cold. There are many lessons to be learned here. The first is that Antarctica is a harsh environment that severely tests your equipment-Murphy's Law rules in Antarctica. The second lesson is that the simpler the piece of equipment, the easier it is to identify and fix problems. The sled's construction is simple-there are few moving parts and anything sensitive to moisture and freezing is enclosed in a weatherproof housing. The third, and most important, is the need to be very familiar with how a parcticular piece of equipment works. In this case, Darren had designed the sled, so knew where each component was located and how it was supposed to work. Basically, it all comes down to using that most basic of all scientific tools, the scientific method, as you systematically work through the mystery and develop and test a series of hypotheses until the root problem is identified. Of course, in Antarctica you hope that the problem is one that can be fixed in a land of limited resources.
The process for photographing and weighing the seals is pretty straightforward. Using a boom-mounted digital camera (the pictures at the end of this journal will help you understand what that looks like) you take pictures of both the mother and its pup. A stick, marked in 20 cm intervals, is included in the photo for use as a scale during analysis. Photographs are taken of the seal from above and from the side. Once all the seals are photographed, it's time to weigh them. The scale is pulled into place with a snowmobile, set into position, and is ready to go.
Okay, enough for theory, here's how it really works. A number of factors conspire to make each step as difficult as possible. First of all, you need to remember where you are-it's Antarctica. What does that mean? It's cold and windy and the snow surface is anything but level. It's difficult to hold a camera attached to a 5-foot long boom steady in the best of conditions. Now imagine doing that when the wind is blowing at 15-20 mph. Then there's the issue of manual dexterity needed to operate the camera. Usually you wear a thin pair of liner gloves underneath your warm gloves. The liners definitely help with keeping your fingers flexible, but they don't do much to keep them warm-the other crucial element needed for dexterity. Consider the difficulties involved in keeping a digital camera operating under cold conditions. Battery life is shortened and electronics don't always work the way the manufacturer intended. Then, there's the seals. Getting a seal to stay still for a photo is kind of like asking a small child to sit still while you set up an elaborate portrait shot. While some seals sit resignedly throughout the process, most squirm about as you hover over them with a camera and the scale stick. Both photographer and photographee jockey for position in an elaborately choreographed dance.
The weigh sled is designed to give an accurate weight within seconds of placing the animal on the scale. It averages the weights determined by each sensor and displays the weight on a digital screen. Getting a pup's weight is straightforward-drag the pup to the sled and weigh them. Their mothers are a different story. There's very little you can do to persuade a 400-500 kg animal to do something it doesn't think is in its best interest. We work in teams of three-one to get the pup to the sled and hold it on the scale while the other two stand by to help guide the mother onto the sled after her baby. When she is on the scale we remove the pup and read her weight on the digital readout, then let her exit. Then we put the pup back on to get its weight. After this we reunite mother and pup on the ice and back off to let them settle down. Sometimes, no matter what we do, the mothers just do not get on the scale. In those cases we simply stop, weigh the pup, and end the ordeal before either seal or researcher become overly stressed.
Today we were able to photograph and weigh 6 pups. Their mothers, however, were a different story. While all were photographed, only one deigned to get on the scale. Once a seal is photographed you have 24 hours to weigh her. We will come back tomorrow after we weigh the remaining pup/mother pairs to see if we can coax any more moms onto the scale.
Enticing them onto scales
Waddle right up please
Contact the TEA in the field at .
If you cannot connect through your browser, copy the TEA's e-mail address in the "To:" line of your favorite e-mail package.