Galapagos Fur Seals
(Arctocephalus galapagoensis, Heller, 1904)
An adult Galapagos fur seal female. Galapagos fur seals are the
smallest pinnipeds. Adult females average only about 28 kg in body mass. Females
become reproductively active at the age of three or four years. Females give birth
to one pup at a time, twins have not been recorded. Pups are born at around 2.5
to 4 kg. By the time they reach one year of age, they weigh about 8.5 to 12 kg.
Galapagos fur seal bulls average about 70 kg in body mass. These fur seals are
highly polygynous, meaning that bulls defend territories, and will mate with multiple
females that use their territories, once they come into oestrus. Bulls usually
cannot successfully hold a territory until they are about 9 years of age, and
then only for about two to three years. Territorial fights amongst bulls can be
quite vicious, and may result in serious injuries.
Galapagos
fur seals have the lowest reproductive rate reported for pinnipeds. The average
growth rate of pups is very low. Weaning occurs typically only at two years of
age, not infrequently can three-year-old fur seals still be seen suckling from
their mom. This young mother is carrying a small VHF telemetry beacon, and an
electronic time-depth-recorder (TDR). We use this type of device to record dive
behavior for periods of up to one month. The TDR is glued to the dorsal fur with
quick-set glue. It will be peeled off at the end of the observation period, and
the recorded data is then downloaded to a laptop computer for analysis.
As
a result of the long period of dependency, and as a possible adaptation to an
unpredictable food supply, overlapping offspring generations do occurr. In this
instance, the siblings directly compete for the mother's milk. Except in years
of ample food supply, the younger sib tends so succumb to the older one in this
direct competition for maternal milk. In this image, the dead pup under the rock
has starved at the age of four weeks. It's older sib, a yearling, was not able
to dive and feed itself efficiently yet, as we were able to determine through
the use of the attached electronic dive recorder (TDR).
To help us understand what limits the diving capabilities of young fur seals,
we draw a small blood sample from the femoral sinus at the time of TDR attachment.
This blood sample is imediately analyzed for hematocrit, hemoglobin concentration
and erythrocyte count. Fabricio Barahon is analyzing a blood sample in this image.
Two young Galapagos fur seals underwater. The one in the front is carrying a TDR.
Another underwater image of a yearling fur seal carrying a TDR. This one is playing
in the surf.
Mario Piu is using a directional VHF antenna and scanner, to track down one of
our study animals carrying a TDR and VHF telemetry beacon.
Tracking down the animals is one thing. Actually capturing them is another. The
coast is extremely rugged.
We use small hoop-nets to capture our study animals. In this picture, Fabricio
and Mario have just caught a two-year old female in the net. This gives you an
idea how small these fur seals are!
Here Fabricio is peeling off a TDR while Mario is holding the animal. The whole
process takes less than three minutes.
That's it for now. I will add more details on what the project was all about, data analysis, finding etc.. in the near future.
In the meantime, check out these publications from this project. For downloadable pdf files of these papers, see the PUBLICATIONS section of the LABB website.
Back to Galapagos
Check out the Galapagos fur seal page of the Seal Conservation Society!
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