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African Penguin Populations Reported in a Puzzling Decline

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Science  02 Mar 2007:
Vol. 315, Issue 5816, pp. 1205a
DOI: 10.1126/science.315.5816.1205a
On the move.

Some African penguins are establishing mainland colonies such as this one as prey becomes scarcer around their island habitats.


PRETORIA, SOUTH AFRICA—African penguin populations, on the upswing since the mid-1990s, appear to have gone into a surprising nosedive. New data indicate that their numbers may have dropped in the past few years by as many as 50,000-40% of the population. And the birds, which normally breed on island colonies, have puzzled scientists by establishing a growing number of new colonies on the mainland.

Marine zoologists see this population pattern reflected in several observations. “Every piece of information we have—breeding success, breeding counts, diet sample analysis, and [a bird census during molting season]—all show the same trend and are serious cause for concern,” says Samantha Petersen, who manages BirdLife South Africa's seabird conservation program.

Zoologist Rob Crawford, a penguin expert with South Africa's Environmental Affairs Department, agrees that the trend is “quite disturbing.” He believes that the birds' prime food sources—sardines and anchovies—are becoming scarce around established colonies. Although overfishing may be part of the problem, Crawford and South African fish experts also blame “a large eastward shift” in the distribution of the fish. In a recent study, they found that the biomass of those fish species in the region near the penguins' largest breeding islands west of Cape Town fell sharply after 2002.

In what Crawford suspects is a “desperation move” to get closer to their fish prey, some penguins—apparently from island colonies—have been moving eastward and settling on the mainland, most recently at the De Hoop Nature Reserve. They normally shun these locations because of predators. Les Underhill, who directs the University of Cape Town's avian demography unit, agrees that the new colonies reflect a trend of penguins moving eastward toward the current fish biomass center, near Mossel Bay.

African penguins, called jackass penguins because of their braying, once numbered more than 1.5 million on islands off South Africa's western coast. But guano and egg harvesting a century ago led to a 90% decline in the population; oil spills in 1994 and 2000 also held them back. Even so, South African penguins climbed to about 120,000 earlier in this decade before the most recent downturn.

Long-term oceanographic studies are needed to assess whether climate change could be a factor. For now, South Africa's environment department is considering various short-term options to try to protect the penguins, including establishing no-fishing zones around several breeding islands. Underhill contends that “setting up areas around breeding colonies which are closed to fishing is the critical issue facing penguin conservation today.”

This month, Crawford's group will begin a new count of nests and, later, of penguins themselves during molting. Researchers are also using satellite-tracking and transponders to analyze the birds' feeding habits. Parallel efforts are ongoing in Namibia, where the number of penguins is now about 24,000, down from 100,000 in 1956.

Life is not likely to get easier for South Africa's penguins, threatened by oil spills, predators, and habitat changes. But Underhill says the new colony at De Hoop offers some hope: It shows that the penguins might be safely relocated. If scientists could figure out how to start colonies, “then we could secure a piece of coastline from land predators and get a colony going near the fish.”

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