Harpij 3 2008
California Sea lion ESB
Gerard Meijer
Ouwehands'
Dierenpark
The
EAZA European Studbook (ESB) for California sea lions has
its origins from information on California sea lions
residing in Dutch zoos that was gathered in 1986 for a
research project to establish how to breed these animals
successfully while avoiding inbreeding.
Three zoos (Rotterdam,
Rhenen and Hardewijk) had already been breeding this species
since the late 1970’s. Some Belgian zoos joined the
studbook in 1987. This studbook became the first official
ESB during the annual IUDZG meeting in Singapore in 1991.
The first edition of the studbook was published in 1993, and
much information has been gathered since. There has been
great effort in the last two years to get all the errors out
of the studbook before the transfer to ZIMS. Record keeping
in European zoos is improving very steadily, but there are
still challenges. The sex of many animals has been
misidentified, and it has often been difficult to establish
which animal is which when they have moved to a new zoo via
an animal broker or dealer.
The
original population consisted of 38 animals, most of which
were wild-caught. The European population is expected to
reach 500 in the next 5-10 years, with at least six
generations having been born. The first thorough analysis of
the studbook data was made in 2000, after the studbook data
were transferred from ZR-book, the program previously used
in Europe, to SPARKS. It could then be seen that 40% of all
the individuals from a population of 340 animals were
descended from one male “Polly” from Rhenen Zoo. With
some effort, this has been decreased to 30% of the
population. While California sea lions do not live longer
than 17 years in the wild, females have reached 30 years of
age in Europe, but males live slightly less long. Because
sea lions live in harems and the sex ratio hovers around
1:1, there are always surplus males. The most frequently
asked question by ESB participants is whether there are
females available, and the second most asked is whether a
home can be found for a young male. Zoos prefer to hold a
breeding group, and it is not easy to convince them to hold
a bachelor group.
The
author recounts some amusing incidents in which helping zoos
to receive animals, or trying to work with zoos to improve a
situation, has not gone as hoped. Despite these incidences,
and the problems in having all the information in the
studbook correct, he finds it very rewarding to be working
with “his” animals, and the often nice people involved.
He is also pleased that by being the ESB keeper for these
animals, he has been able to help the captive California sea
lion population.