Text: Rebecca Duncan.
Standing a little under two feet tall and dressed in a tuxedo, the African penguin—or Spheniscus demersus—is heading towards the brink of extinction. The population of these seabirds has declined by 65% since 1989. Where hundreds of thousands of breeding pairs once occupied the shores of Dassen and Robben islands, now there are a mere 3,000. What is causing this decline? Severe weather and climate change, oil pollution, egg collection for human consumption back in the twentieth century, and disease have all played a role. However, it has recently become clear that one contributing factor stands above the rest: a shortage of food near breeding colonies.
In 2018, the sardine fishery in Namibia was closed after over-fishing from decades prior led to a crash in the sardine stock. The sardine population has yet to recover. At the same time, the penguin population has collapsed. In South Africa, the forage fish shifted eastwards between 1996 (anchovy) and about 2002/2003 (sardine), and the penguins underwent a recent, rapid decline (having been recovering for a while) from about 2004/2005 onwards. This may be related to climatic effects on ocean circulation or fisheries, or most likely both – but at this point, food availability for the imperiled penguin is the main problem that requires immediate attention.
The latest Editor's Choice article in ICES Journal of Marine Science is a synthesis of 11 years of study in South Africa that tracked penguin populations across four breeding colonies in relation to nearby commercial fishing. The researchers describe how a “gold-standard” of field experiments has revealed how fisheries targeting small pelagic fish (SPF) are competing with these seabirds for food, especially during the penguin’s breeding season. Fisheries that target sardines and anchovies were stopped from fishing close (within 20 km) to seabird colonies on South Africa’s Eastern and Western Cape for two-to-three-year periods, and government, academic, and conservation fisheries and seabird scientists documented the survival rate of penguin chicks and the feeding behaviours of adults from nearby colonies.
Peak breeding season for African penguins is during the Austral winter, and females can lay two eggs in each nesting attempt. The pair then take turns keeping the eggs warm and tending to their chicks once they hatch. While one stays on watch, the other will go forage. These birds need to catch approximately 20% of their body weight each day, which is quite the feat for a bird that weighs only 3+ kilograms. The work of feeding themselves and their brood requires a lot of calories; the experiment has shown that commercial fishing near colonies makes this job harder.
Despite penguins being mobile creatures with the ability to forage well beyond their neighborhood beaches, parent penguins prefer to stay local to dive for fish while their mate is safeguarding the chicks. However, at least partly as a result of the decreased anchovy and sardine availability, African penguins have become the most vulnerable penguin species on the planet. The authors of the synthesis have hope, though. They write that when fisheries around the penguin colonies in South Africa closed—even temporarily—the breeding success of nearby birds increased substantially.
Not surprisingly, there is debate as to whether the results of this study are certain enough to support more permanent closure of the fisheries in the vicinity of colonies. Closure of a fishery represents an economic loss to the coastal communities that they support. This study indicates that continuing to restrict fishing near key colonies could offset approximately 20% of the annual penguin population decline which could help in the conservation of the penguins and support other economic benefits such as ecotourism.
An adult penguin coming back from a day feeding at sea at Robben Island, South Africa in 2015. The penguin was looking for a suitable place where to 'land' due to the rocky wave-swept shoreline that rims the island. At other locations, penguins may make landfall on sandy beaches.Photo: Davide Gaglio.