ZooNooz Article - MARCH 2008

A trio with potential

Story by Annie Toluzzi
Photographs Annette Petersen

Taronga has acquired two new Leopard-seals, both washed up in the same week of August last year but in different locations on our Sydney coastline. Casey, a one-year-old male was discovered at Wattamolla in
the Royal National Park and Sabine, a larger three-year-old female was found almost on the doorstep at Clontarf.

Both seals were in poor condition, exhausted, suffering significant weight loss, weakened by parasitic infections and sporting numerous Cookie-cutter Shark bites. As such they were, for all their fierce reputation, rather lethargic and easy to catch. The reason for their beaching is thought to be due to the seasonal lack of food in their Antarctic range which has caused them to venture closer to shore in search of prey. Here they have probably been caught in currents, become lost and disorientated and, in their weakened state, washed up far from home on our beaches.

Although now fully rehabilitated, Casey and Sabine will not be released back into their wild habitat. This decision is based on the Antarctic Treaty which states that rescued animals are not to be released back into their natural populations due to the risk of introducing disease acquired during their captivity. So Casey and Sabine have joined Brooke, the zoo’s longterm resident, to form a trio of Leopard-seals as a major attraction in the eagerly awaited Great Southern Oceans exhibit.

But being on display is only one of the future roles for our new Leopard-seals. These three are the only Leopard-seals in captivity and will thus provide huge educational benefits for the Australian Marine Mammal Research Centre and the public. Research on non-captive Leopard-seals has been limited as they are difficult to study in the wild, being rather elusive and their habitat at times inaccessible. Leopard-seals live on the pack ice of the Antarctic which is highly sensitive to changes in global warming. Since they also breed on the pack ice, their population numbers and general well-being act as barometers for detecting changes in the Southern Ocean ecosystem. Our Leopard-seals are thus considered environmental ambassadors for their species. One of the benefits for the zoo and the public will therefore be the opportunity to learn more about them and from them.

Already in progress is a study of their dietary history to discover what they have been recently eating and comparing this to diets of fifty years ago. Strangely enough it is from their whiskers that we get this information. Each of the food types eaten by the Leopard-seals contains specific carbon/nitrogen markers and after absorption by the body these specific signatures are laid down in their hair and whiskers, similar to rings of a tree. So analysing the isotope levels in individual whiskers and taking periodic photos to map whisker growth then comparing results with museum specimens, will allow researchers to predict the future impacts of food availability on Leopard-seal populations. Also being investigated is the question of whether Leopard-seals use some form of echolocation when hunting for their prey. A research station, similar to one used in dolphin echolocation studies, has already been set up in their exhibit.

Very little is known about Leopard-seal behaviour compared to other marine mammals. Dr Tracey Rogers is the current expert on Leopard-seals and has been studying their courtship behaviour in the wild. So the prospect of having a young male and female at Taronga will provide exciting opportunities for her to continue her behavioural study. Leopard-seals lead a solitary life unlike other seal species which congregate en masse to mate and rear their young.

Dr Rogers has only ever seen one Leopard-seal pup in the wild. Although solitary, Leopardseals are not nomadic; they have distinct territories and a breeding season in which they seek potential mates by singing to each other. There are no immediate plans in place however, for a breeding program at the zoo. Unit Supervisor Danielle Fox will explore the possibility carefully, as much space and expertise will be required. In the meantime a concentrated program of training for the two new seals is well underway.

At present the Leopard-seals are being kept in separate enclosures as their keepers gradually familiarise them with one another with the aim of putting them together in the neutral territory of their Great Southern Oceans exhibit. This needs to be a carefully monitored process as Brooke, a mature female over three metres in length and weighing 350 kilograms, is likely to show territorial dominance over the younger newcomers.

According to Supervisor Elle Bombonato, the Leopard-seals have quite different personalities. Casey the male is relaxed and easy-going whereas Sabine tends to be feistier, requiring higher maintenance. Carla Litchfield, a behavioural scientist from Adelaide, is currently looking at different behavioural enrichment options for the Leopard-seals and this no doubt will be a rewarding experience for both the seals and their keepers! All in all, there is much to look forward to for Taronga’s unique trio.

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