Australian sea lions in jeopardy

Dramatic fluctuations in sea lion pup mortality remain a mystery.

March 20, 1998
Web posted at: 6:24 p.m. EDT (1824 GMT)

By Environmental News Network staff

Mysterious deaths of Australian sea lion pups are prompting scientists from an Australian governmental research organization to call for more intensive research into the species.

"The Australian sea lion is an endemic species which we need to take care of. It's a tourist icon, up there with the koala, which attracts tens of thousands of visitors to the sea lions' colonies every year. If we don't find out why their numbers are not increasing, we may face more serious problems later on," said Dr. Peter Shaughnessy, principal research scientist with the Division of Wildlife and Ecology.

The Australian sea lion has its principal breeding colonies at Kangaroo Island and Dangerous Reef near Port Lincoln in South Australia. Smaller colonies exist on the west coast of South Australia and in Western Australia.

"Data collected suggests to us that too many pups are dying and we don't really know why," says Shaughnessy. "For example in 1996 at two colonies we found mortality rates of 30 percent and 50 percent respectively."

The following year mortality decreased to only 4 percent among Dangerous Reef sea lions but the worry is that we have no idea what's causing these dramatic fluctuations in pup mortality, says Shaughnessy.

Possible causes of death include parasites, such as hookworm; environmental disturbance causing food shortage for lactating female sea lions; high rates of aggression by adult males; direct human harassment; and interaction with fishing gear.

The Australian sea lion is the only seal that does not have a strict, annual breeding cycle

Another possibility, says Shaughnessy, is that sea lions may be facing stronger competition for food from their cousin, the New Zealand fur seal, whose numbers are increasing on Kangaroo Island at an annual rate of around 10 percent.

Shaughnessy, recognized as an international authority on sea lions and fur seals, suggests the Australian sea lion population in 1998 may be no greater than it was before European settlement of Australia.

One of the complicating factors in trying to solve the mystery of why sea lion numbers are not increasing is the creature's unique breeding cycle. Of the 35 seal species in the world, the Australian sea lion is the only type which does not have a strict, annual breeding cycle.

A female sea lion will give birth to a pup after an 18-month cycle, meaning that her pupping season occurs in alternate summers and winters, or in alternate springs and autumns.

While calling for more scientific study of Australian sea lions to try to maximize their breeding potential, Shaughnessy has welcomed the steady growth of New Zealand fur seal numbers, especially in South Australia.

He says it is clear from his team's most recent count of New Zealand fur seals in the summer of 1998 that the species is recovering from its over-harvesting by sealers in the last century and early 20th century.

"Each year we return to South Australia we find greater numbers and new colonies, some of them admittedly quite small, and we should all be thankful that these wonderful creatures are making a healthy comeback," says Shaughnessy.

New Zealand fur seals are also found in Western Australia, off southern Tasmania and occasionally in New South Wales.

Shaughnessy has carried out research on the subject in conjunction with National Parks and Wildlife South Australia staff based at Kangaroo Island and Port Lincoln.

Copyright 1998, Environmental News Network, All Rights Reserved

Related CNN stories:

• Sea lion pups struggle against El Niñ:o's wrath - February 15, 1998
• The sea lions return to Punta Loma - April 1, 1997

Related ENN Stories:

• Scientists probe Steller sea lion decline
  
• Seals, sea lions got prehistoric eviction notice
  

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