Oil leaves its mark on penguins

By John Yeld

Cape Town - Research just published shows that African Penguins oiled and subsequently cleaned and released during the Treasure oil spill crisis in June 2000 are not breeding as well as their non-oiled counterparts.

This surprising result, which runs counter to previous findings about penguins oiled during the earlier Apollo Sea oil spill in 1994, will result in scientists and conservationists involved in seabird rehabilitation modifying their efforts in the future.

And one of the authors of the research, University of Cape Town (UCT) Avian Demography Unit director Les Underhill, said the finding confirmed the importance of avoiding oil spills.

"Its take-home message is a plea to keep oil out of the sea in the first place. We can clean the penguins, but they are not quite as good as new," he said.

After the stricken bulk ore carrier MV Treasure sank off Cape Town, around 19 000 oiled African Penguins were collected - the largest number yet contaminated in a single oil spill incident.

Around 15 000 were from the Robben Island breeding colony. Robben and Dassen islands are the major breeding grounds of this now-threatened species, whose numbers plummeted during the 20th century.

In all, 17 287 penguins oiled in the Treasure spill were cleaned, rehabilitated and released back into the wild in the biggest such operation yet attempted.

Every bird involved was banded, allowing researchers to monitor their subsequent breeding success.

Previously, a study at Dassen Island had found no long-term difference in the reproductive success of birds that had been oiled by the Apollo Sea spill and their non-oiled counterparts.

A similar study was conducted on Robben Island between 2001 and 2005, when the breeding success of birds oiled in the Treasure spill was measured against non-oiled birds in terms of fecundity (fertility), hatching success and fledging (chicks) success.

The team included researchers from the University of Bristol in Britain, UCT, the Marine and Coastal Management branch of the Environmental Affairs and Tourism Department, and the Robben Island Museum.

"We anticipated that, if Treasure birds were hampered in any way, it would be during the pre-fledging period when food demand was at its peak," the researchers stated.

This is exactly what they found: fledging success in non-oiled penguins was 61 percent while in birds oiled by the Treasure it was just 43 percent - a significant difference. And the higher mortalities were mostly in older chicks.

The researchers suggest that factors contributing to this difference could be the long average interval between capture and cleaning (22 days) and between capture and release (48 days) in the case of the Treasure birds.

This was around 20 percent longer than the Apollo Sea operation, and twice as long as the time taken by Sanccob (SA National Foundation for the Conservation of Coastal Birds) to rehabilitate and release individual oiled birds brought in.

Also, they speculated that the toxicity of the heavy bunker oil that spilled from the Treasure could have been a factor.

Referring to the higher mortality rate of older chicks, the researchers pointed out that as chicks grow, their nutritional requirements increase.

"It appears that birds oiled in the Treasure spill were less able to meet this increasing demand than other birds, either because their overall health was not as good or they had less experience breeding with their mates," the research team said.

"Should a similar large spill occur in future, every effort should be made to treat oiled birds as quickly as possible to reduce the risk of their suffering a similar reduction in breeding productivity.

"Further, the other interventions, such as relocation of unoiled birds and captive-rearing of orphaned chicks, may need to receive higher priority than hitherto."