The plight of the African penguin – found in Namibia and South Africa – highlights the dangers to wildlife of the sudden rise in temperature caused by human-induced global warming.
For the penguins have learned to look for places with lower sea temperatures and large amounts of a type of chlorophyll. These are tell-tale signs of plankton and, in turn, the fish that feed on them.
These once sure-fire ways to find large shoals are now leading the penguins into an “ecological trap” that is pushing them closer to extinction.
And the situation has been made worse by industrial-scale fishing and a raft of other problems, mostly caused by humans.
According to the International Union for Conservation of Nature (IUCN), there are about 80,000 adult African penguins left. But oil slicks in 1994 and 2000 killed some 30,000 birds and the death toll “may increase” if planned harbour developments go ahead, the IUCN says.
In the new study, researchers from Exeter and Cape Town universities tagged 54 juvenile birds from eight different colonies to find out where they go to look for fish.
The areas they chose were once rich hunting grounds for sardines and anchovies.
But changes in water temperature and salt content have prompted the fish to move hundreds of kilometres away.
One of the researchers, Dr Richard Sherley, of Exeter University, said this meant the tell-tale signs used by penguins to find fish “now put them in danger”.
“These were once reliable cues for prey-rich waters, but climate change and industrial fishing have depleted forage fish stocks in this system,” he said.
“Climate change and fisheries are transforming the oceans, but we don't have a complete understanding of their impact.
“Our results support suspending fishing when prey biomass drops below certain levels, and suggest that mitigating marine ecological traps will require major conservation action.”
The problems in finding food have produced low survival rates among juvenile African penguins, previously known as jackass penguins.
It is thought breeding numbers are about 50 per cent lower than they would be if the birds were able to find enough to eat.
Animals in decline
Animals in decline
1/8 Harbour seal (Phoca vitulina)
Where: Orkney Islands. What: Between 2001-2006, numbers in Orkney declined by 40 per cent. Why: epidemics of the phocine distemper virus are thought to have caused major declines, but the killing of seals in the Moray Firth to protect salmon farms may have an impact.
2/8 African lion (Panthera leo)
Where: Ghana. What: In Ghana’s Mole National Park, lion numbers have declined by more than 90 per cent in 40 years. Why: local conflicts are thought to have contributed to the slaughter of lions and are a worrying example of the status of the animal in Western and Central Africa.
3/8 Leatherback turtle (Dermochelys coriacea)
Where: Indonesia, Malaysia, Mexico, Costa Rica. What: Numbers are down in both the Atlantic and Pacific. It declined by 95 per cent between 1989-2002 in Costa Rica. Why: mainly due to them being caught as bycatch, but they’ve also been affected by local developments.
4/8 Wandering albatross (Diomedea exulans)
Where: South Atlantic. What: A rapid decline. One population, from Bird Island, South Georgia, declined by 50 per cent between 1972-2010, according to the British Antarctic Survey. Why: being caught in various commercial longline fisheries.
5/8 Saiga Antelope (Saiga tatarica)
Where: Kazakhstan, Mongolia, Russia, Turkmenistan, Uzbekistan. What: fall in populations has been dramatic. In the early 1990s numbers were over a million, but are now estimated to be around 50,000. Why: the break up of the former USSR led to uncontrolled hunting. Increased rural poverty means the species is hunted for its meat
6/8 Swordfish (Xiphias gladius)
Where: found worldwide in tropical, subtropical and temperate seas. Why: at risk from overfishing and as a target in recreational fishing. A significant number of swordfish are also caught by illegal driftnet fisheries in the Mediterranean
7/8 Argali Sheep (Ovis mammon)
Where: Central and Southern Asian mountains,usually at 3,000-5,000 metres altitude. Why: domesticated herds of sheep competing for grazing grounds. Over-hunting and poaching.
8/8 Humphead Wrasse (Cheilinus undulatus)
Where: the Indo-Pacific, from the Red Sea to South Africa and to the Tuamoto Islands (Polynesia), north to the Ryukyu Islands (south-west Japan), and south to New Caledonia. Why: Illegal, Unregulated and Unreported (IUU) fishing and trading of the species
Dr Stephen Votier, also of Exeter University, said the ability to track the penguins movements was a “crucial tool in conservation biology”.
“This ecological trap was only discovered when young penguins were tracked from multiple colonies,” he said.
“This highlights the power of studying animal movements, particularly for long-lived marine species like penguins.”
The results of the research were published in the journal Current Biology in a paper called Metapopulation tracking juvenile penguins reveals an ecosystem-wide ecological trap.
According to the IUCN’s Red List of endangered species, the African penguin is “undergoing a very rapid population decline, probably as a result of commercial fisheries and shifts in prey populations”.
“This trend currently shows no sign of reversing, and immediate conservation action is required to prevent further declines,” it adds.