South Africa: Plunging Penguin Population Puzzles Professors
Johannesburg — SCIENTISTS are puzzling over the rapid demise of the African Penguin, one of SA's most charismatic tourist attractions.
Every year tens of thousands of visitors flock to Boulders Beach in Simon's Town to see the waddling birds, inhabitants of one of the world's few readily accessible colonies.
They may become a still rarer sight if scientists fail to find a way to boost the penguins' dwindling numbers, which have fallen by more than 50% over the past 30 years. The drop prompted BirdLife International to reclassify the birds earlier this year, from "vulnerable" to "endangered".
"We are really wrestling with the issue," says Prof Les Underhill, director of the University of Cape Town's (UCT's) animal demography unit. "If we knew exactly what the problem was we could do something about it."
Spheniscus demersus -which means "plunging wedge" - is the only penguin native to Africa, and was once abundant in both SA and Namibia. In the early 1900s there were more than 1-million on Dassen Island alone.
Overzealous guano harvesting and egging decimated their numbers, and by the time the first census was conducted in the 1950s, only 150 000 breeding pairs remained. Today there are fewer than 26 000 breeding pairs worldwide, 21 000 in SA.
This is a dangerously low number as the colonies are now so small that they are vulnerable to previously insignificant events such as bad weather or Kelp Gulls stealing eggs.
"The collapse in recent years has been alarming ... every colony north and west of Cape Point has shown a very large decrease in numbers," says Dr Robert Crawford, a specialist scientist with the Department of Environmental Affairs.
Many scientists agree the penguins' survival is closely linked to availability of sardines and anchovies, their main food source. But precisely how this affects their capacity to breed is not yet clear. Prof Underhill is investigating whether they are failing to fatten up sufficiently before they moult because they are being forced to forage over greater distances, while others are focusing on what happens during their breeding season.
Penguins typically forage within 30km of their colonies while feeding chicks, so if the fish stocks shift even a short distance, breeding birds are in trouble.
Since the late 1990s, the availability of anchovies on the west coast has fallen dramatically as the fish stocks have shifted eastwards , increasing competition for food from other penguins and from the local fishing industry. Some scientists think the fish shortage may be a short- term phenomenon, and that once their numbers improve, so too will those of the penguins.
"Claims that it's overfishing are rubbish," says Janet Coetzee, who chairs the government's pelagic scientific working group. "It's just recruitment failure."
The numbers of anchovies available on the west coast depend on new, young fish joining the population each year. "These are short-lived species. If you have six years of low recruitment, combined with an eastward shift, it has a big impact. The penguin decline is very alarming, and we are looking at closing sensitive areas around colonies to fishing. Whether this will have an effect is unknown."
But some scientists think there may already be a case for creating a no-fish zone around vulnerable penguin colonies.
A study published this year by the Royal Society found penguin foraging efforts fell 30% after a 20km zone around their home of St Croix Island in Algoa Bay was closed to purse seine fishing during the breeding season.
Birds breeding on Bird Island 50km away increased their foraging during the same period, suggesting even small protected areas could immediately benefit the vulnerable birds.
"Stopping fishing close to colonies may not be enough to help the penguins," says Peter Ryan, one of the paper's authors and an associate professor at UCT's Percy FitzPatrick Institute. "Gaining a better understanding of the local movements of fish in relation to fishing pressure is a key priority. But the onus should be on the fishing industry to show the dramatic decrease in penguin numbers is not due to their activities.
"Pelagic fish are quite mobile, and if fishing effort is displaced only a short distance there may still be too few fish for the birds. Gaining a better understanding of the local movements of fish in relation is fishing pressure is a key priority," he says. "But the onus should be on the fishing industry to show that the dramatic decrease in penguin numbers over the last decade is not due to their activities."