The African penguin, also known as the jackass penguin, is found exclusively in southern African waters. These penguins got their nickname from their loud, throated call that is remarkably similar to that of a donkey. Under normal circumstances, there’s something quite funny about seeing such a small animal make such a donkey-like bray, but with the way things are shaping up for the jackass penguin, their call evokes more of a wail of despair.
The African penguin has been under pressure for centuries because of human exploitation: throughout the the 1800s humans harvested their excrement, known as guano, for the use in fuel and explosives; throughout much of the 1900s humans harvested their eggs for consumption; and more recently, humans have been overfishing the anchovies and sardines in the region, the penguins’ main food supply.
So it isn’t too surprising that penguin populations have been in somewhat of a free fall in recent years. In 1956, when the first full census of the species was conducted, there were 150,000 pairs of penguins. By 2009, there were estimated to be only 26,000 pairs left, representing a loss of over 80% in 50 years. And now, a new study released in Current Biology shows that juvenile penguins are dying as they search for food in empty oceans.
After juvenile penguins gain their independence, they disperse into the ocean, traveling up to 2,000 km away from their natal colonies. Penguins will head for ocean waters that have low temperatures and have high concentrations of chlorophyll-a, which have typically been indicators of nutrient rich waters that contain sardines and anchovies. But, the new study found that climate change and overfishing have changed the abundance and location of the penguins’ main diet; even worse, the young penguins aren’t able to take into account these changes to their environment, and swim hundreds of kilometers searching for food that isn’t there.
The international team of researchers used satellite tracking to follow the dispersal of juvenile penguins from their breeding grounds. "When the young of this endangered species leave the colony for the first time, they travel long distances, searching the ocean for certain signs that should mean they have found an area with lots of plankton and plenty of the fish that feed on it,” explained the study’s lead author, Richard Sherley of the University of Exeter and University of Cape Town. “But rapid shifts caused by climate change and fishing mean these signs can now lead them to places where these fish, the penguins' main prey, are scarce with impacts on their survival—a so-called 'ecological trap.”
The hunting grounds for these penguins have historically been one of the most productive ocean areas in the world, filled with anchovies and sardines. While the region’s population of penguin food has been diminished by years of overfishing, the region’s phytoplankton distributions have remained largely intact. This presents a problem for the penguins, because they rely on plankton distribution as signage for their food. "These were once reliable cues for prey-rich waters, but climate change and industrial fishing have depleted forage fish stocks in this system," Sherley said, “"The penguins still move to where the plankton are abundant, but the fish are no longer there."
The effects are quite severe, with the study suggesting that penguin “breeding numbers are 50% lower than if non-impacted habitats were used.” With only about 25,000 breeding pairs left, the African penguin can’t take much more before it starts down the slippery slope of extinction. Still, Sherley and his colleagues are hopeful; by working with regional governments to implement better fisheries management, the penguin food supply could be improved. Hopefully future generations will be able to listen to the cry of the jackass penguin with a clean conscience.