Adult African penguin at the edge of the Robben Island colony.

The way adult penguins hunt and the body condition of their chicks are both directly linked to local fish abundance and could potentially inform fishery management. This is according to a new study involving University of Cape Town (UCT) researchers. The researchers studied an endangered African penguin colony during a rare three-year closure of commercial fisheries around Robben Island, South Africa.

“Understanding how African penguins forage to feed their chicks in their variable marine environment can help us identify conservation measures for these endangered populations,” said Dr Kate Campbell, who led the research at UCT.  

“A three-year commercial fisheries closure around Robben Island created a unique opportunity to study how African penguins directly respond to natural changes in local abundance of their prey – anchovies and sardines.”

 

“A three-year commercial fisheries closure around Robben Island created a unique opportunity to study how African penguins directly respond to natural changes in local abundance of their prey – anchovies and sardines.”

Fishing is often considered to be one of the biggest drivers of biodiversity loss in the ocean. It is so widespread that we lack an understanding of the ‘natural’ relationships between marine predators and their prey, and thus the extent to which predators are disrupted by competition from fisheries.

This is a critical knowledge gap since many marine predators such as penguins are considered indicator species: a species whose success indicates the condition of their habitat.

The researchers found that the abundance of anchovies and sardines was directly linked to the foraging behaviour of African penguins and the conditions of their chicks.

The researchers estimated fluctuations in population size of prey fish over three years within the area that the fishery was closed (a 20-kilometre radius around Robben Island). Over the same time, the researchers also monitored adult penguins’ fishing behaviours. At the Robben Island colony, the team also measured the diet of breeding adults and the body condition of chicks.

They found that the abundance of anchovy and sardine was directly linked to the foraging behaviour of African penguins and the conditions of their chicks. This is a common assumption about predator–prey relationships that has rarely been tested in the absence of fishing.

When fish abundance was lower, the penguins increased the effort they put into foraging by foraging for longer, swimming further and diving more often. This likely explains why the body condition of the chicks also declined: finding fish became more challenging for breeding adults and required more energy.

“Interestingly, the variation in foraging behaviour between individuals also increased when prey fish were scarcer,” said Dr Richard Sherley of the University of Exeter.

 

When fish abundance was lower, the penguins increased the effort they put into foraging by foraging for longer, swimming further and diving more often.

“While some ‘superstar’ penguins find food easily, others are less successful,” he added. “Once food gets harder to find, more individuals will start to struggle and work harder, but they will do so at different rates, increasing the variation we see in foraging effort.”

The results indicate that penguin foraging behaviour and chick condition could be key indicators for local fish abundance, making a case for their inclusion in monitoring the health of local ecosystems.

“Since these short-term changes will likely have knock-on effects for chick survival and penguin population size, they could be used as powerful early warning signs to inform fisheries’ policies and marine conservation efforts,” said Campbell.

 

The results indicate that penguin foraging behaviour and chick condition could be key indicators for local fish abundance.

“Technological advances also mean there’s exciting potential to better understand how these endangered penguins behave when prey resources are scarce,” she added.

“Hopefully, in the future, we could aim to effectively balance fishery management with penguins’ needs, to reduce the impact on local economies whilst maximising the benefits to our oceans,” Sherley concluded.

• Campbell KJ, Steinfurth A, Underhill LG, Coetzee JC, Dyer BM, Ludynia K, Makhado AB, Merkle D, Rademan J, Upfold L, Sherley RB (2019) Local forage fish abundance influences foraging effort and offspring condition in an endangered marine predator, Journal of Applied Ecology 00: 1–10.

Story:  Supplied

Photos:  Richard Sherley