For islands to qualify as suitable for penguins, they needed to offer protection from land-based predators and had to be surrounded by suitable foraging grounds for sardine and anchovy within a 20km radius. Supplied
Twenty-two thousand years ago, at least 15 large islands on the West Coast of Southern Africa teemed with hundreds of millions of marine birds and penguin colonies.
Between 15 000 to 7 000 years ago, sea levels rose by 100m, slowly submerging these large islands until only small hilltops and outcrops remained above water.
Over the past 22 000 years this resulted in a ten-fold reduction in suitable nesting habitat for African penguins, sending the population numbers of these “climate refugees” into steep decline.
This is the paleo-historical picture of the geographical range of African penguins, which has been developed by scientists at the evolutionary genomics research group in Stellenbosch University’s School for Climate Studies. Their study was published in the African Journal of Marine Science on Thursday.
The authors hope their research sheds light into the current vulnerability of Africa’s last remaining penguin species, whose population is sliding towards extinction with just 10 000 breeding pairs left in South Africa. African penguins are endemic to South Africa and Namibia.
This paleo-historical image of “multiple millions” of the flightless seabirds “stands in stark contrast to the current reality of a post-1900 collapse of the African penguin population”, Heath Beckett, the study’s first author, said in a statement.
In 1910, Dassen Island, which is off the Cape West Coast and is about three square kilometres, had an estimated 1.45 million penguins. By 2011 South Africa’s entire African penguin population had collapsed to 21 000 breeding pairs. By 2019, they numbered just 13 600 pairs. About 97% of South Africa’s current population is supported by only seven breeding colonies.
Historical islands
As penguins prefer to breed on islands to escape mainland predators, the team used topographic maps of the ocean floor off the coast of Southern Africa to identify potential historical islands lying at 10m to 130m below current sea levels.
For islands to qualify as suitable for penguins, they needed to offer protection from land-based predators and had to be surrounded by suitable foraging grounds for sardine and anchovy within a 20km radius.
Assuming that sea levels were much lower during the last Ice Age, they identified 15 large islands off the West Coast, the largest a 300km2 island lying 130m below the sea surface.
Taking into account rising sea levels over the past 15 000 to 7 000 years, they identified 220 islands that would have provided suitable nesting conditions for penguins, of which 216 are less than 1km2 in area, while some are as small as 30m2, “barely bigger than a rock”.
Today, the five largest islands off the West Coast are Robben Island (5km2), Dassen Island (3km2), Possession Island (1.8km2) and Seal and Penguin islands (1km2). Possession, Seal and Penguin islands are off the Namibian coast.
The scientists estimate between 6.4 million and 18.8 million penguins could have occupied the Southern Cape waters during the Last Glacial Maximum. They calculated penguin populations based on the earliest available population density estimates and island area, assuming that penguins usually nest at about 500m from the shore.
Major changes in habitat availability
Beckett said the study’s main objective is to show that there have been major changes in habitat availability over the past 22 000 years. “This could have had a massive effect on penguin populations. These populations are now experiencing additional human pressures on top of this in the form of climate change, habitat destruction and competition for food.”
The researchers said that although their results of significant population declines raise concerns, they also highlight the resilience of African penguins that could be used for their conservation and management.
“African penguins are almost certainly pre-adapted to an appreciable level of habitat change via relocation, and it’s likely that this capacity underpins the African penguin’s ability to establish new colonies fairly quickly under suitable conditions.
This flexibility provides an opportunity for conservation responses that can make available suitable breeding space, including mainland sites.
But for these responses to be successful, sufficient marine food is critical to prevent the species extinction.
Guy Midgley, interim director of the School for Climate Studies and a co-author of the study, said the charismatic seabird is a “total survivor” and given half a chance, they will hang on. “Island hopping saved it in the past; they know how to do this.”
Expert panel
In February, Barbara Creecy, the minister of forestry, fisheries and the environment, announced that she had appointed an expert review panel to advise on managing the interactions between the small pelagic fishery (anchovy and sardines) and the conservation of African penguins.
In September last year, her department announced the interim closure of some areas around major penguin colonies to commercial fishing for anchovy and sardine from September 2022 to mid-January as a precautionary measure aimed at ensuring the survival of the species while balancing ecological and socio-economic interests.
The limitation on fishing was extended to mid-April 2023 and the department said in February that further decisions will be made depending on the work schedule of the panel. It will review all related science outputs over recent years, including the outcomes of the island closure experiment it had undertaken over the past decade.
The panel will advise the department on the appropriateness and value of fishing limitations for penguin trends. “This is a key issue as the sardine stock in local waters remains at low levels. Competition for food is thought to be among one of the pressures contributing to the decline of African penguin populations,” it said.
Other pressures include shipping traffic and the associated noise and vibrations, pollution and degradation of suitable nesting habitats through historical removal of guano and coastal commercial, and residential developments.
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