Leopard seal diets are reshaping Antarctic ecosystems

We used to think leopard seals had broad diets, but new research suggests that many individuals are picky eaters – with big consequences.

While the species as a whole eats many prey types, individual seals often specialize. This pattern has ecosystem-wide effects, especially in the predator-rich waters off Cape Shirreff.

Leopard seals prefer specific diets

The research team analyzed stable isotope values (δ15N and δ13C) from 46 whiskers of 34 seals. This long-term data covered a decade.

The results showed that 59% of the seals were dietary specialists, 28% were intermediates, and only 13% were true generalists.

Specialists fall into two categories. High trophic level specialists likely hunt fur seal pups and large fish. Medium to low trophic level specialists target krill, penguins, and cephalopods.

The research suggests that individual differences in diet shape local food webs more than previously assumed.

“Even though leopard seals as a species eat a wide variety of prey, most individuals actually focus on just a few types of food,” said study co-author Dr. Emily Sperou from Baylor University.

“This means that a few highly specialized seals can have a much bigger effect on certain prey populations than we previously thought.”

Some seal diets don’t change

The study revealed two long-term foraging styles. Some individuals, like seal 397, maintained high trophic level specialization for up to ten years.

Others, like seal 12, changed diets significantly across five years, from specialist to generalist.

This variability suggests behavioral flexibility. Seals might shift strategies depending on prey availability or competition. Such changes could buffer the species against ecosystem shifts.

“A few specialists can help shape entire ecosystems,” said study co-author Dr. Patrick Charapata.

“Understanding these patterns in leopard seals and other top predators can help us better predict and manage changes to prey populations and the greater ecosystem these species live in.”

Leopard seal diets and prey populations

Larger female leopard seals were found to consistently feed at higher trophic levels compared to males. This means they targeted prey that are themselves predators or occupy higher positions in the food web.

Interestingly, all the individuals identified as high-level dietary specialists in the study were female. Their greater body size likely plays a key role in this pattern.

Bigger seals are physically capable of capturing and consuming larger, more energy-dense prey, such as Antarctic fur seal pups. This access to richer food sources gives them an energetic advantage and increases their impact on prey populations.

Individuals with a large impact

The data also showed that females had broader isotopic ranges in their whisker samples. This suggests they influence a wider range of the ecosystem through their feeding habits. They do not just eat more; they affect more parts of the food web.

A few large females were found to be responsible for most of the observed predation on fur seal pups. One individual, identified as seal 397, stood out in particular. She had the highest number of recorded pup captures in the study.

Her method involved ambush style attacks, showing strategic hunting behavior that likely made her even more effective. This highlights how a small number of powerful individuals can have an outsized effect on an ecosystem.

Diets change with prey numbers

The data revealed a sharp drop in δ15N values between 2015 and 2017. This trend aligns with a known decline in Antarctic fur seals and some penguin species. Researchers believe the drop reflects a reduction in nitrogen-rich prey.

From 2017 to 2023, the number of leopard seals at Cape Shirreff fell by 76 percent. The few that remained, like seal 397, regained access to higher trophic prey. As competition dropped, δ15N values began rising again.

The study reshapes how we think about predator roles. Individual specialization can reshape ecosystems. Just a few high-impact predators may shift prey dynamics dramatically.

For instance, a pod of five orcas once consumed 8,500 sea otters annually. Leopard seals may be exerting similar pressure on fur seal colonies.

Current conservation strategies often assume that all individuals in a species behave alike. But this study warns against such assumptions. Ignoring individual-level behavior might cause poor management decisions, especially under climate stress.

Leopard seals and prey dynamics

The study relied on stable isotope data but did not include direct prey identification. Future research could pair isotopic signatures with tracking and observational data.

While this study was focused on Cape Shirreff, genetic data indicate that these findings may apply to leopard seals across the Southern Ocean.

The research shows how a few individual predators can shape the fates of entire species. Leopard seals remind us that even in the coldest oceans, personal dietary choices matter.

The study is published in the journal Ecology and Evolution.

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