Every few years, there is in South America a climatic change, called "El Nino" (also called ENSO = El Nino Southern Oscillation).
This means "Christ-child", because it happens in the same period. On that moment the water surface is very warm and poor on food. The colder, food-rich layers are pushed down and the phytoplankton has to follow when it needs food. Therefore, the places with much light (necessary for the photosynthesis) are those places with less food and vice versa. The phytoplankton starves, and while krill needs this plankton to survive, it decreases too. The anchovies and other fishes who need this krill, are forced to follow the stream and move to colder, more southern waters. Because Humboldt penguins need those fish, they have to follow too and must give up their brood and desert their chicks in search for food.
This "El Nino" takes place about every ten years (intervening periods decreasing), followed by the opposite phenomena "La Nina", where the water surface is much colder. Each change, the entire ecological system needs time for recovery. When on that moment people fish too much anchovies, this "recovery" is in danger and this could cause a collapse of the anchovies stocks and is a threat for the penguins too.