Male southern elephant seals are extremely picky eaters

Given their size and status as one of the top predators in Antarctica, one might expect that male southern elephant seals are indiscriminate feeders. 

However, new research from UNSW Sydney reveals that these elephant seals are surprisingly picky eaters, preferring specific favorites over the wide array of food choices available in their Antarctic habitat.

Unexpected findings 

Study lead author Andrea Cormack is a PhD candidate at UNSW Science. “They could have the pick of the buffet, and yet each male southern elephant seal eats a lot of the same food, which is just a fraction of what’s on offer,” said Cormack. 

“So, they are extremely picky eaters, each with their own unique favorite foods they go after, whether it be fish, squid species, crustaceans or octopus.”

Extreme specialists 

The research provides one of the first in-depth insights into the diet of adult male southern elephant seals. Compared to their female counterparts, the dietary habits of these males, who can weigh up to four tons, have been relatively understudied. 

Interestingly, while female seals maintain a specialized diet, the males’ preferences are far more extreme.

“We didn’t specifically compare males to females in this study,” said Cormack. “But females are known to maintain a fairly specialized diet between one another, just nowhere near as extreme as what we found with the males in our research.”

How the research was conducted 

Studying these creatures in their natural habitat poses significant challenges due to their size and temperament. Instead, the research team analyzed whiskers collected from 31 male seals. 

The whiskers contain stable isotopes that provide a chemical record of the seals’ diet over time. This method allowed the researchers to construct the most comprehensive picture yet of the males’ dietary habits, encompassing up to a year of eating behavior per seal.

“These guys are out in the water foraging for months, and then fasting for two to three months on land during breeding season, so it’s hard to gather a lot of information about their diet through study methods like stomach analysis,” said Cormack. “But by analyzing hard tissues that store an inert chemical record of what they’ve eaten, we can start putting together the pieces about their eating habits.”

Key insights 

The study revealed that nearly all the sampled seals were specialists, consistently eating the same types of food with little variation. A majority were extreme specialists, feeding on less than 20% of the available food types, while only one seal demonstrated a more generalist diet.

“The Antarctic ecosystem has a lot of variety, but male southern elephant seals don’t like to mix it up,” said study senior author Professor Tracey Rogers. “They each have their own favorite foods, and they stick to them despite all the options available.”

Consistently picky 

An interesting correlation emerged between body size and dietary specialization. Larger seals tended to eat higher up the food chain, opting for energy-dense prey like large squid, especially leading up to the breeding season. 

However, size was not the sole determinant of specialization, as even smaller seals showed extreme pickiness in their diet from early adulthood.

“They were all consistently picky on their food type regardless of size,” said Cormack. “For these guys, who can lose up to 50 percent of their body weight during the breeding season when they’re fasting on land, what you choose to eat could be very important.”

Study significance 

Cormack noted the significance of these findings, especially considering the potential impact on breeding success. The specialization in diet could be driven by various factors, from physical attributes like gape size to fluctuations in food availability.

According to the experts, this specialization may help improve foraging success rates between male seals and allow them to gain the size needed to compete with other males for breeding rights.

“We know from previous studies that individuals will often return each year to the same feeding grounds in search of their favorite foods,” said Cormack. “But we need more studies to be confident about exactly what’s driving specialization and how it impacts breeding success.”

The study is published in the journal Marine Ecology Progress Series. 

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