|....The development of
miniature dataloggers to record what marine mammals do underwater
has given us information on how deep the animal is diving, how fast
it is going, the light levels and temperatures underwater, and even
the sounds it hears. However we still have little idea of why it is
....Sometimes animals dive
straight down and then come straight up again. At other times they
dive straight down and then stay at one depth for several minutes
before returning to the surface to breathe. Is the first one a quick
but unsuccessful look to see what's there, whereas in the second the
animal spends time feeding?
....By taking photographs of
what the animal is exposed to while it is underwater we are able to
answer some of these questions.
Insight developed a digital video camera modified to withstand the
high pressures that these animals are exposed to at depth (pressures
up to a hundred times what we feel at the surface).
....The camera controls
respond to the measurement of depth, for example it can switch on
the video when the animal goes deeper than 10 metres. This means it
can take pictures during selected parts of dives. There is red-light
flash on the camera (red is on the edge of what seals can see and so
will disturb them less than a bright white flash).
....The pictures above were
taken by the camera when it was put on Antarctic fur seal mothers at
South Georgia. These mothers stay ashore to feed their pup for two
days and then go out to sea to feed themselves for five or six days
before returning to feed their pup again, repeating this for three
or four months. A camera was attached to the fur of each female for
one of these trips and then taken off when she returned a week
later. Almost all of the pictures showed krill and several showed
....The fact that seals eat
krill is not new, however, this technology gives a minute-by-minute
loook at what an animal is doing and what it is exposed to, giving
information about the decision-making process of the seal,
investigating questions such as whether the depth and thickness of a
krill swarm affects if it is worthwhile for a seal to bother diving
to feed on it.
....The pictures are useful
for interpreting the behaviour of the seal and also in studying the
krill themselves. Krill are not easy to study at sea, but are at the
crux of the Antarctic marine ecosystem.
....Observations of krill are
generally made by collecting them in nets, monitoring them with
acoustic echosounders, or occasionally by observations from scuba
....Fur seals are presumably
much better at finding dense patches of krill than we are, and the
observations they record on these cameras (in terms of school
density, individual krill orientation within the swarm, the depths
at which they are found and how these change with time of day) will
provide an added dimension to the study of krill in the Antarctic.
....Please note, the images
shown have had the quality reduced for fast loading. Click here if you
would like to study the images taken by the Venus Underwater Camera