The Last Glacial Maximum (LGM) of 22,000 years ago saw fifteen large islands swarming with hundreds of millions of marine birds and penguin colonies.
The Last Glacial Maximum (LGM) of 22,000 years ago saw fifteen large islands swarming with hundreds of millions of marine birds and penguin colonies. Sea levels rose up to a hundred metres between 15 and 7 thousand years ago, covering these islands until only small hilltops and outcrops remained above water. This caused a tenfold reduction in suitable nesting habitat for penguins in Africa, leading to a steep decline in their population numbers.
Scientists from Stellenbosch University’s (SU) evolutionary genomics research group in the Department of Botany and Zoology and the School for Climate Studies created this paleohistorical map of the geographic range of African penguins.
They hope to shed new light on the current vulnerability of the last remaining penguin species in Africa with this effort.
The research was published on April 20, 2023, in the African Journal of Marine Science under the title “A natural terminal Pleistocene decline of African penguin populations enhances their anthropogenic extinction risk.”
According to Dr. Heath Beckett, the first author of the article and a postdoctoral fellow at SU’s School for Climate Studies, this paleohistorical image of numerous millions contrasts sharply with the current reality of an African penguin population collapse after 1900.
A three square kilometre island off the West Coast known as Dassen Island was home to an estimated 1.45 million penguins in 1910.
But by 2011, only 21,000 breeding pairs of African penguins remained in South Africa, and by 2019, that number had dropped to just 13,600. Only seven breeding colonies support roughly 97% of South Africa’s current population. The African penguin was listed as endangered by the International Union for the Conservation of Nature in May 2005.
So what did southern Africa’s southern and western coastlines look like during the last Ice Age? What does it have to say about the size of the penguin population? The researchers used topographic maps of the ocean floor off the coast of southern Africa to identify potential historical islands lying ten to 130 metres below present sea levels because penguins prefer to breed on islands to avoid predators on the mainland.
Islands needed to provide protection from land-based predators and be surrounded by suitable foraging grounds for sardines and anchovies within a 20-kilometer radius in order to qualify as suitable for penguins in Africa.
They discovered 15 sizable islands off the West Coast, with the largest measuring 300 km2 and lying 130 metres below the water’s surface. They made the assumption that sea levels were significantly lower during the last Ice Age.
The researchers then determined 220 islands that would have offered suitable nesting conditions for penguins, of which 216 are smaller than one km2 in area and some are as small as 30 m2, barely larger than a rock. They did this by accounting for the rising sea levels over the previous 15,000 to 7,000 years.
Presently, Robben Island (about 5 km2), Dassen Island (about 3 km2), Possession Island (about 1.8 km2), Seal Island, and Penguin Island are the five largest islands off the West Coast of Southern Africa (both below 1 km2). Off the coast of Namibia are Possession Island, Seal Island, and Penguin Island.
They then calculated penguin population estimates based on the available island area using the earliest population density estimates, assuming that penguins typically nest at most 500 metres from the shore.
They calculate that 6.4 million to 18.8 million people could have lived in the southern Cape waters during the Last Glacial Maximum using this method.
But between 15,000 and 7,000 years ago, as sea levels rose, the habitat used by African penguins to nest drastically declined.
Dr. Beckett claims that the study’s main goal is to demonstrate that the availability of habitat has changed significantly over the past 22,000 years. “Penguin populations might have suffered greatly as a result of this. These populations are now additionally under pressure from humans due to climate change, habitat destruction, and food competition,” he clarifies.
Although this finding raises serious issues, the researchers contend that it also highlights the possibility of an African penguin reserve of resilience that could be used to support its management and conservation in the face of a bleak future.
Dr. Beckett clarifies: “Breeding colonies of penguins in Africa would have needed to relocate numerous times over the course of centuries, if not even shorter periods of time, and there would have been fierce competition for breeding space as the size of the island habitat shrank significantly. Given the historical adaptability of response, conservation managers have some latitude to provide suitable breeding space, even on mainland sites, as long as suitable nesting sites are provided.”
Prof. Guy Midgley, interim director of SU’s School for Climate Studies and a co-author, believes that penguins have a strong colonisation ability due to millennial-scale selection pressures. However, given the rise of modern human pressures, penguins may not stand a chance.
To prevent the extinction of penguins in Africa, sufficient access to marine food resources remains a vital element of a coordinated response. This is due to the competition between the commercial fishing industry and humanity for the same food source.