A recent study shows South African Penguins being affected by an Ecosystem-wide Ecological Trap, contributing to a decrease in population size, and their endangered status.
The study, undertaken by Dr Richard Sherley of the University of Exeter, entailed the tracking of Juvenile penguins to reveal this Trap.
In recent years, the South African Penguin species Sphensicus Demersus has become endangered after seeing a rapid decline in population size. This is thought to be due to commercial fisheries and shifts in prey populations. This research shows that both of these factors, as well as climate change, contribute to creating what are known as Ecological Traps, where food is scarce.
The penguins that the researchers monitored where shown to disperse to three main foraging regions off the western coast of South Africa. These regions were previously rich in sardines and anchovies, the penguins’ main prey, but are currently void of such fish. The scarcity of sardines in particular in these regions is strongly linked to the low survival of these juvenile penguins. Therefore, the areas which the penguins now disperse to are considered as Ecological Traps.
“Environmental degradation can cause maladaptive habitat selection, meaning cues which used to work for a species now put them in danger,” said first author Dr Richard Sherley.
“Juvenile African penguins look for areas of low sea temperatures and high chlorophyll-a, which indicates the presence of plankton and therefore the fish which feed on it. These were once reliable cues for prey-rich waters, but climate change and industrial fishing have depleted forage fish stocks in this system.”
Not being able to determine the definite mechanism behind choosing these traps, Sherley suggests that there may be an innate control in the dispersal selection; but he believes that this can’t explain the targeting of specific areas alone. He writes that adult penguins seem less at risk of falling into these traps, which indicates that this species refines its foraging skills over many years. He also highlights that social information passed on from adult birds who select the correct region seems unlikely, as adults actively exclude juveniles from foraging groups and move to different areas.
Juvenile penguins are very vulnerable to forage fish depletion, so Sherley calls for further conservation efforts to be put in place in order to limit the consequences of heightened juvenile mortality. The immature dispersal of these birds is important to gene flow, which in turn has an impact on their adaptability to change. A reduced adaptability would be disastrous to the species’ survival as a whole.
African penguins are on the IUCN List of Endangered Species since 2010, due to a decrease in population size from approximately 70,000 pairs in 1978 to 9,300 in 2015. Conservation efforts are therefore underway, including monitoring of population trends, protecting most breeding areas, decreasing predation of eggs, chicks and grown birds, but also reducing extensive industrial fishing and limiting the increasing effects of climate change.
- Sherley et al. (2017) Metapopulation Tracking Juvenile Penguins Reveals an Ecosystem-wide Ecological Trap, Current Biology 27, 1-6
- IUCN Red List of Threatened Species (2000) Spheniscus Demersus (African Penguin, Black-Footed Penguin, Jackass Penguin) [online], available: http://www.iucnredlist.org/details/22697810/0 [accessed 22 Feb 2017].