Published by the Communications
and Development Department
9 December 2003
While most New Zealanders gear up for Christmas parties, shopping
and holiday feasts, Canterbury University biologist Dr Louise Chilvers
is preparing to spend the holidays on a cold and isolated Subantartic
Island in order to help save the world’s rarest sea lion species,
the New Zealand sea lion.
New Zealand sea lions are the country’s only endemic pinniped
(wing-footed marine mammal), and they once occupied most of the country’s
coastline. However, sealing in the nineteenth century nearly eliminated
the species, restricting the animals to the Subantarctic Islands.
Unlike their close relative, the New Zealand fur seal, New Zealand
sea lions have never recovered.
Dr Chilvers, who is on a FRST-funded postdoctoral fellowship with
Dr Neil Gemmell from the School of Biological Sciences, is part of
a team of researchers who are trying to understand why sea lions are
still so threatened.
December is the prime study time for Dr Chilvers, because this is
when females congregate to give birth to their pups. This will be
her third summer in the Auckland Islands, where she has been studying
a group of about 600 sea lions on Enderby Island.
Dr Chilvers hopes that her research on the feeding and diving behaviour
of females will help “get the NZ sea lion off the threatened
species list”. The research will also help in the management
of local squid fisheries by determining how trawlers overlap with
the foraging patterns of sea lions.
“We have known for some time that trawlers catch sea lions in
their nets, but we are now finding that resource competition is also
important.”
The local fisheries mostly target squid, which probably makes up at
least 10-20% of the sea lions’ diet, but the fisheries also
catch significant amounts of fish, both as by-catch and also during
low squid years.
“We’re not saying that they’re overfishing. But
it’s like restricting all humans to one island. They are not
historically based there, and so any added stress can lead to decline.”
Similar studies in the northern hemisphere have shown that populations
of a related species, the stellar sea lion, declined because fisheries
removed preferential fish species.
Dr Chilvers studies the NZ sea lions’ feeding behaviour by marking
females with a tracking device called a time depth recorder, which
records the depth of the sea lion every five seconds. Dr Chilvers
can then compare this data against depth maps to determine where the
sea lions are feeding.
So far she has collected feeding behaviour data on 18 tagged females.
These data indicate that sea lions’ feeding patterns overlap
considerably with the squid fisheries, and that individual sea lions
have very diverse foraging habits. Some individuals prefer to stay
close to Enderby and others range over 150 km away.
This variation amongst individuals may indicate that sea lions learn
specific feeding habits when they are young, and Dr Chilvers is anxious
to test these preliminary results further with another season of data.
Dr Chilvers is travelling to Enderby Island with three Department
of Conservation staff members who are also studying the sea lion population
there.
The team is prepared for another busy Christmas of fieldwork rather
than opening presents and eating Christmas cake.
“I’m afraid Christmas day is the same as any other day
– if not busier. It is pretty much birth day for the pups, which
means we have lots of pups born around that time and therefore lots
of weighing and measuring. As for New Years, we all just sleep through
it.”
Still, the satisfaction of helping this threatened species survive
is great enough that she said, “there is nothing else I’d
rather be doing”.
For more information contact:
Dr Neil Gemmell
School of Biological Sciences
Ph 03 364 2009
Email neil.gemmell@canterbury.ac.nz
