Posted on 28/02/2013 by Phillip Island Nature Parks
During a trip to Seal Rocks in January, researchers from Phillip Island Nature Parks recorded 3,725 Australian fur seal pups, compared to 5,600 in 2007.
Dr Roger Kirkwood, a research scientist at the Nature Parks, speculates that the difference compared to five years ago is due to poor feeding conditions last year. This could have influenced the ability of adult females to maintain their pregnancy.
“We don’t understand all the mechanisms that cause changes in prey available to seals each year, but it likely relates to fluctuations in major water currents,” said Dr Kirkwood.
The pup estimate, conducted every five years at Seal Rocks since 1992, usually coincides with estimates at all Australian fur seal colonies. The surveys are a collaborative effort between researchers and government agencies in Victoria, Tasmania, South Australia and New South Wales.
Researchers are keen to find out the status of the seals at other sites and what sort of between-year variability there will be in pup production at Seal Rocks. A grant from the Australian Marine Mammal Centre will allow a full survey next summer.
“The species wide survey links in with annual estimates that are conducted at several of the smaller colonies. The combined surveys are an important method for monitoring the seal’s population status and range over time,” said Dr Kirkwood.
“We are unsure what the population is doing at present. It experienced an increase during the 1980s and 1990s, perhaps into the 2000s, but now may be levelling off.”
Researchers from Phillip Island Nature Parks undertake several trips to Seal Rocks each year to deploy satellite trackers, remove plastic debris from entangled seals and monitor diets through the collection and analysis of seal scats.
Changes over time
During the late 1700s and early 1800s, more than 240,000 fur seal skins were exported to China from Bass Strait. The seal fur was extracted and turned into hats and clothing. Australian fur seals, like other fur seal species, are now believed to be recovering from the exploitations.
The boom and bust of commercial sealing was rapid, but was followed by a sustained subsistence harvesting industry that continued in Bass Strait until 1923. As other fisheries developed, seals were viewed as competitors and culls by fishermen kept numbers low. Australian fur seals became a fully protected species in 1975. Numbers have increased since then, possibly in part due to legislated protection.
In 2007, following the last species-wide estimate of pup numbers, which was led by researchers from the Nature Parks, the Australian fur seal population was estimated at approximately 120,000 seals - at the lower end of numbers that are thought to have been in Bass Strait prior to sealing.
“It is interesting to consider one of our ancestors’ first ventures into Bass Strait all but eliminated one of the region’s key marine predators, and the ecosystem has been in recovery for the last 200 years,” said Dr Kirkwood.
“What was the Bass Strait ecosystem like prior to European settlement?”
About Phillip Island Nature Parks
Phillip Island Nature Parks is a self-funded, not-for-profit organisation. Funds raised through ecotourism operations are invested into conservation, research and education activities.
Seal count reveals change in pup numbers
Danene Jones - Communications Executive
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