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Penguin poo reveals secrets to hoiho colony's health, and raises concerns

Blue cod has been identified as making up a large proportion of the yellow-eyed penguin (hoiho) diet, causing concern, according to University of Otago researchers who examined the penguins' excrement.

A yellow-eyed penguin (hoiho) and two chicks. Source: Supplied

The research, published in journal Wildlife Research earlier this month, found that blue cod occurred in all of samples and accounted for more than 55 per cent of the DNA sequences identified.

The prevalence in their diet of a single fish species has raised concern for the resilience of the endangered animal and highlights the importance for measures such as the protection of marine habitats, researchers said of the findings. 

Study co-author Ludovic Dutoit noted that a healthy diet has previously been shown to be important for breeding success and survival.

“Yellow-eyed penguins are known to be highly selective feeders, and traditionally their diet has consisted of a small number of fish and squid species,” Dutoit said.

“To find that their current diet is dominated by blue cod, and very few other prey species, is not what we would have liked to have found.”

In a first for assessing the diet of New Zealand’s penguins, the hoiho research team, based in the Department of Zoology, used DNA analysis of hoiho faeces to reconstruct what the birds were eating.

Lead author and PhD candidate Melanie Young collected over 300 faecal samples from hoiho along the Otago coast for the study. The research team then extracted a specific gene found in all animals - Mitochondrial 16S - to help identify individual prey species in their diet.

Co-author professor Yolanda van Heezik - whose research in the 1980s indicated the delicate relationship between diet quality, quantity, breeding success and survival of hoiho - raised concerns about the absence in the diet of several key species that were available to hoiho four decades ago.

Recent video footage has also confirmed the absence of the fish in the marine environment where penguins forage.

“Excessive reliance on one or very few prey species is unlikely to promote resilience in this beleaguered species, and highlights the importance of protecting marine habitats through the creation of marine reserves that encompass penguin foraging habitat,” van Heezik said.

The penguin faeces, which can be collected from around nests while penguins are away at sea, has proven an efficient and non-intrusive way to capture baseline diet information that can be compared to future data collected.

Many more penguins can also be sampled through the collection of faeces than tracked using cameras, making DNA sampling of faeces ideal for monitoring long-term diet trends of many individuals at multiple breeding sites, researchers said. While the approach does not reveal other important information about foraging, it can be used in combination with other methods to provide a glimpse into underwater activity, they said.