A team of scientists has found that endangered African penguins are struggling because they’re trying to find food in areas that no longer contain enough fish to sustain them. Juvenile penguins are foraging in habitats based on qualities that used to signify food. Overfishing and climate change has caused the fish to move, however, and young penguins can’t catch on quick enough. The findings are in a paper that was just published in the journal Current Biology.
African penguins (Spheniscus demersus), also known as black-footed penguins, are found on coasts throughout southern Africa. The bulk of their diet consists of fish and squid. Their main prey species, anchovies and sardines, are also consumed by humans. Overfishing and recent oil spills are considered to be two of the major drivers of their rapid population decline, leading to the placement of African penguins on the endangered species list. Captive-breeding programs have been established in an attempt to save the species.
Researchers from the University of Exeter collaborated with scientists from the University of Cape Town to better understand the reasons behind the sharp decline in African penguin populations. New information could help with conservation efforts. The team used satellite tracking to observe penguins at eight research sites. They focused on juvenile penguins, which currently have very low survival rates. The researchers tracked 54 individual penguins to see where they ended up after gaining independence.
The team found that the juvenile penguins were falling into an “ecological trap.” Ecological traps occur when the environment changes or degrades rapidly, before animals can evolve or learn new coping mechanisms. In the case of the penguins, the trap was leading to another phenomenon called maladaptive habitat selection, in which animals choose poor habitats based on old cues. The juvenile penguins were seeking out habitats with cooler water and high levels of chlorophyll-a, an indicator of plankton-rich waters. These habitats used to contain large numbers of sardines and anchovies, which prefer cool temperatures and eat plankton. Unfortunately, these cues no longer mean the regions contain fish. Fisheries have been established in these areas, leading to sharp drops in the fish populations. To make matters worse, these same fish are migrating to new areas due to temperature and salinity changes caused by climate change.
The team’s study shows that African penguins have fallen into an ecological trap. Juveniles are choosing habitats based on old ecological cues but these areas no longer contain the penguins’ main food sources. Anchovies and sardines are being overfished; both fish species are also migrating as climate change affects water conditions. This deadly combination is leading to starvation and explains the low survival rates for juveniles. These issues need to be taken into account when developing conservation plans for African penguins.
Sherley et al. Metapopulation Tracking Juvenile Penguins Reveals an Ecosystem-wide Ecological Trap. Current Biology (2017).