Weddell Seal Foraging Behavior
This project is a continuation of a previous project, where we used similar technology to our current telemetry system, but under much more controlled conditions. Now, we are applying the telemetry system toanimals that are free to move around in the entire McMurdo Sound area.
We are expanding this page as we are progressing with our research, so keep checking back with us. Here is a first preview:(click on images to enlarge):
What in the world is this?
Above is a screen shot of a video image recorded by a Weddell seal on the bottom of McMurdo Sound, at a depth of about 450 meters. The image is recorded by the Video Data Aquisition Platform, VDAP, a telemetry concept first proposed for use on pinnipeds by Randy Davis about 12 years ago. The VDAP system records images captured by a head mounted video camera on a tape system carried by the seal in a backpack. This system however is much more than a pressure proof video recorder. The unit is controlled by several microporcessors, and records a large varitey of data. This data allows us to perform dead reckoning and reconstruct the three-dimensional dive path of the seal, after recovery of the data.
In the coarse image above, one can just recognize the seal head, with the two slightly lighter eyebrows of the seal to the left and right, and the snout with some whiskers at the center. The seal is crusing along the bottom of the sound, and right in front of the snout is an invertebrate organism, possibly a bryozoan.
In the view below you can see how this image was photographed right off the TV screen that Matt is using to review the video tape for behavioral analyses.
Above is Godzilla, the second seal outfitted with the VDAP this season. Godzilla is wearing the backpack which cannot be seen in this image, as well as the headmounted camera. The camera is mounted to a neoprene rubber patch that is glued to the fur.
So how do we do all this, what information do we gather with the VDAP system, and why do we do this? Let's step back a bit and start from the beginning:
Above, you can see Weddell seals hauled out of the water, and resting on the ice. On cold, windy days few seals can be found hauled out. On warm days, many seals are basking in the sun. In the foregound, a seal mother is nursing her pup.
Peak pupping in McMurdo Sound occurs in November. Pups are born with a soft coat of very warm, lightly colored fur, called Lanugo. This will keep them warm until they can grow a thick blubber layer by nursing from their mother.
Mother and pup recognize each other by their calls, and by smell. They vocalize frequently. The mother will call, and the pup answers with a bawl. This reinforces mutual recognition.
First, we capture a seal and bring it to our experimental area in the Jamesway. To capture the seal, we use the seal sled towed behind the spryte:
The two images above actually show the release of an experimental animal during one of the preceeding years, but you get the idea...
Once we bring an animal to Weddell World, it is immobilized and weighed in a sling suspended from scale hung under a large beam:
Ok, so that is not a seal in the sling. Bill and Randy are being hoisted up to test the weighing setup.
In the image below, you can see parts of the VDAP system. The core of the main unit (right) is pulled out of the black cylindrical housing (left). This core unit contains a vido tape recorder, the main processors and solid state data storage, batteries to power the system, and on the outside connectors to plug in other systems components. Two of these can be seen sitting in front of the VDAP: a flux-gate digital magnetic bearing sensor is located in a smaller cylinder, and the video imaging sensor (camera head) is located to the right of it.
To attach the main VDAP unit, we use what we call a saddle:
This saddle - here shown being prepared for deployment - is attached to a large piece of neoprene, which in turn is glued to the dorsal fur of the seal. The saddle consists of a fairing made from syntactic foam. This streamlines the system and adjusts the overall buoyancy to a neutral state.
In the image below, you can see the saddle on the seal's back, with the VDAP nesting in the cradle of syntactic foam. The video imaging sensor is mounted on the seal's head in a similar manner. The complete instrument package is designed to be neutrally buoyant and streamlined. The gear is removable via quick-release mechanisms. This seal shown here is recovering from the sedation, before we let it enter the water.
After recovery, the seal enters the water, and after a short times dives away through the hole that was drilled through the sea ice underneath the experimental section of the Jamesway. On the side of the seal two transmitters are visible, a VHF beacon as well as an ARGOS compatible PTT. We will use these two devices to locate the seal, once it will haul out on the ice sometime within the next 2-6 days. That's when we will remove the VDAP to view the video tape and download the digital data for analysis. If the gear looks undamaged, we may swap the VDAP with another unit, to continue recording data from the same animal for another one or two sessions. Below is an animal on which we have just swapped the VDAP units.
