King penguins see no alternative to lanternfish | Polarjournal
Ratmanoff walkers return to the colony on foot when they haven’t landed directly on it from the sea. Image: Camille Lin

A Franco-Canadian study of king penguins in the largest colony on the Courbet Peninsula in Kerguelen shows that these birds are highly specialized, making them vulnerable to geographical changes in the polar front.

King penguins obstinately hunt lanternfish to feed their chicks, even if access to this resource is diminishing. So they intensify their hunting effort and stay at sea longer. These are the latest findings from the Centre d’Études Biologiques de Chizé and McGill University’s Natural Resource Sciences, published in Ibis, the International Journal of Avian Science, on November 12.

In practical terms, this is how the parents work. While one partner regurgitates, little by little, the contents of his stomach, ensuring that his youngster always has something to eat, the other spends between five and twelve days at sea. “They go beyond the polar front,” explains Émile Brisson-Curadeau, PhD student and principal author of the study.

The latter visited the Kerguelen archipelago three times, between 2019 and 2022, and worked on the Ratmanoff colony with the support of the French Polar Institute. One of the largest in the world, with over 100,000 pairs that gather around an estuary, on the heights of an immense dark sandy beach, facing the Southern Ocean.

The early career scientist has equipped some nesting birds with GPS to track their movements. On their return, he took blood samples, to complete a follow-up that has been running since 2015. These samples were used to measure carbon and nitrogen isotopes in the blood.

Birds congregate between the freshwater lake and the sea. The landscape is very flat in this part of the archipelago. Image: Camille Lin

What can nitrogen and carbon reveal about the animal’s diet? These two chemical elements form the basis of most of the molecules that make up living beings, and when penguins draw on the food they consume to regenerate, they accumulate the isotopic signatures of their prey.

“We study blood because it renews itself very quickly and proves useful for associating isotopes with sea journeys. Unlike feathers, another indicator, which are renewed during moulting, which takes place long before the breeding period”, he explains.

Isotope signatures show that king penguins have been concentrating exclusively on lanternfish, and GPS data reveal longer times at sea in the event of unsuccessful fishing.

These birds could have switched targets, hunting squid or other fish species. “Of all the closely related species, king penguins are by far the most specialized,” notes Émile Brisson-Curadeau. “They are therefore more sensitive to changes in the distribution of lanternfish.”

A fluctuating front

The distance from the polar front is therefore decisive for the colonies. The lanternfish live to the south of this front, on the Antarctic side. Around Kerguelen, it runs along the southern part and then climbs to the east of the island, off Ratmanoff. Here, “the front doesn’t move too much because it is constrained by underwater canyons offshore”, he explains.

On the other hand, on Crozet and Marion Island, the front moves away when summers are warm. This makes it harder for the colonies to reach it. “They’re at the mercy of the temperature,” says the researcher. Other colonies, such as those in South Georgia, should not feel these effects, because the island is located to the south of these currents.

This latest study provides the scientific community with new information for observing king penguins. Émile Brisson-Curadeau insists: king penguins are hyper-specialists and “from their behaviors, we can learn about changes in their prey and in the ocean.”

Camille Lin, PolarJournal

Link to study: Brisson-Curadeau, É., Bost, C.-A., Cherel, Y., Elliott, K., n.d. King Penguins adjust foraging effort rather than diet when faced with poor foraging conditions. Ibis n/a. https://doi.org/10.1111/ibi.13287.

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