What happens to Antarctic seals when sea ice vanishes?

In a groundbreaking study, scientists have discovered that when sea ice disappears, Antarctic seals fall silent. 

The research was conducted by Dr. Ilse van Opzeeland and her team at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and the Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg (HIFMB).

Dr. Opzeeland’s team analyzed audio recordings from an underwater microphone that automatically captured the vocalizations of marine mammals such as seals and whales. 

“What’s unique about our study is that, for the first time, we were able to assess recordings covering eight years and all four Antarctic seal species,” said study lead author Dr. Irene Roca, a biologist at HIFMB and AWI at that time, and currently working at the Université du Québec en Outaouais. 

The extensive data collection allowed the researchers to examine the seals’ behavior over an extended timeframe and compare individual years.

What the researchers focused on in the study

The study, published in the journal Frontiers in Ecology and the Environment, was focused on data collected between 2007 and 2014, with the 2010/2011 season proving to be particularly noteworthy. During that time, the research area, situated in the Southern Ocean near AWI’s Neumayer Station III, experienced a significant reduction in ice cover. Less than ten percent of the usually frozen waters had ice, resulting in a near-total absence of sea ice.

This lack of ice had a dramatic effect on the seals’ presence in the area. Audio recordings from underwater microphones showed a significant decrease in seal vocalizations during this period compared to the other seven years of data. 

Antarctic seals rely on sea ice for giving birth and nursing their young, which typically occurs during the Southern Hemisphere’s spring and summer months, from October to January.

Under normal conditions, the sea ice provides an ideal environment for seals to raise their offspring. However, during the 2010/2011 season, the ice all but disappeared. Due to the researchers having installed only one underwater microphone in the area, it remains uncertain whether the seals migrated during this time and, if so, where they went.

Unfortunately, the AWI’s Perennial Acoustic Observatory in the Antarctic Ocean (PALAOA) broke away from the coast along with a calving glacier. In the upcoming Antarctic season, they will install a new underwater microphone on the coast. Installation will begin at the end of this year.

“However, our underwater recordings clearly show that there were far fewer calling seals than usual in the observed waters,” said Irene Roca. This applies, she claims, to all seal species native to the region: the crabeater seal, Weddell seal, leopard seal and Ross seal.

Where the Antarctic seals study was done

Located approximately 2,000 kilometers south of Cape Town in the Weddell Sea, the research area chosen by experts from the Alfred Wegener Institute (AWI) is of particular interest due to its diverse marine life. 

The coastal region in the eastern Weddell Sea is home to all four Antarctic seal species and several species of whale, making it a crucial area for marine research. Scientists believe the region’s abundance of food and typically favorable ice conditions make it an ideal habitat for seals.

However, observations from the 2010/2011 season have raised concerns among the AWI team. If climate change leads to more frequent and extreme variations in sea ice cover, the region may become less reliable as a breeding ground for seals. Recently, the SEA ICE PORTAL reported that below-average sea-ice extents have characterized the Antarctic for the past eight years. Sea-ice extent reached an all-time low in February 2023.

The potential impact of reduced sea ice on seal populations remains unclear due to limited knowledge about the four Antarctic seal species. However, studies on Arctic ringed seals, which are better understood, reveal that the species requires thick snow cover on sea ice to create small caves for their young. Research has shown that many Arctic ringed seal pups perish when there is insufficient sea ice and snow.

“I surmise that the low-ice years also have an effect on Antarctic seals’ reproduction – not only in terms of the young’s survival, but possibly also the adults’ mating behavior or other aspects,” said project coordinator Ilse van Opzeeland.

New equipment will allow the Antarctic seals study to continue

Van Opzeeland considers the eight years of acoustic data collected by the team as a unique asset. Gathering data on seals is typically challenging. Scientists can only count seals from vessels or helicopters. Both options offer limited observational radius. Vessels and helicopters also lack the ability to continuously monitor entire ocean regions.

In contrast, underwater “listening posts” provide round-the-clock monitoring of extensive regions. Additionally, sounds travel farther underwater than in the air. Based on the volume of their vocalizations, some marine fauna can be detected from several kilometers away.

Unfortunately, the AWI’s Perennial Acoustic Observatory in the Antarctic Ocean (PALAOA) recently broke away from the coast along with a calving glacier. Plans to install a new underwater microphone on the coast are in place for the upcoming Antarctic season, beginning at the end of this year. This new installation will continue to provide valuable insights into the lives of Antarctic seals and the potential consequences of diminishing sea ice in their habitat.

This study highlights the potential consequences of declining sea ice for Antarctic seals and the broader marine ecosystem. It serves as a crucial reminder of the importance of understanding and preserving the delicate balance between marine species and their environment, especially as the climate continues to change.

More about Antarctic seals

Antarctic seals are an essential component of the Antarctic marine ecosystem. There are four primary species of seals found in the region: the Weddell seal, the Ross seal, the crabeater seal, and the leopard seal. Each species exhibits distinct adaptations to the unique and harsh Antarctic environment. Here’s a brief overview of each species:

Weddell seals (Leptonychotes weddellii)

These seals are known for their ability to inhabit the icy waters of Antarctica. They have an exceptional diving ability, reaching depths of over 600 meters and holding their breath for up to 90 minutes. Weddell seals primarily feed on fish, squid, and krill. They are very docile in nature. This makes them relatively easy to approach and study.

Ross seals (Ommatophoca rossii)

Ross seals are the least common and least studied of the Antarctic seals. They are relatively small and slender compared to other seals, with a distinctive wide, round head and large eyes. Ross seals are known for their unique vocalizations. They have a diet consisting of fish, squid, and krill. Researchers typically find ross seals in the pack ice surrounding the Antarctic continent.

Crabeater seals (Lobodon carcinophaga)

Despite their name, crabeater seals primarily feed on krill rather than crabs. They have specialized teeth that act as a sieve, allowing them to filter krill from the water. Crabeater seals are the most abundant seal species in the Antarctic region and play a crucial role in the marine food web. They inhabit the pack ice zones and are known for their long, slender bodies.

Leopard seals (Hydrurga leptonyx)

Leopard seals are the most formidable predators among the Antarctic seals. They have a large, reptile-like head and powerful jaws with sharp teeth, making them efficient hunters. Leopard seals primarily feed on other seals, penguins, fish, and krill. They are solitary animals and occupy a higher trophic level in the Antarctic marine ecosystem.

Antarctic seals rely heavily on sea ice for their survival, as they use it as a platform to rest, breed, and give birth to their pups. The effects of climate change on sea ice levels may have significant consequences for the long-term survival of these species and the overall health of the Antarctic ecosystem.

Impact of climate change on Antarctica

Climate change has a profound impact on Antarctica and its marine life, including Antarctic seals. The primary consequences of climate change in the region include rising temperatures, ocean warming, melting ice sheets, and sea level rise. These changes directly and indirectly affect Antarctic seals in several ways:

Loss of sea ice

Antarctic seals depend on sea ice for various aspects of their life cycle, such as breeding, giving birth, and nursing their pups. As climate change leads to a decline in sea ice, seals face challenges in finding suitable habitats for these critical activities. Insufficient sea ice may lead to reduced reproductive success, as seals may struggle to find safe and stable platforms for breeding and raising their young.

Changes in prey availability

Climate change can alter the distribution and abundance of prey species like krill, fish, and squid in the Antarctic region. Changes in prey availability can affect the foraging behavior and diet of seals, potentially impacting their overall health and reproductive success. For example, a decline in krill population due to ocean warming and reduced sea ice may negatively affect crabeater seals, which primarily feed on krill.

Habitat shifts

The decline of sea ice and the rise in ocean temperatures may force seals to shift their habitat ranges in search of suitable breeding and foraging grounds. These shifts could lead to increased competition for resources among different seal species and other marine predators, such as penguins and whales. Additionally, habitat shifts may expose seals to new threats, such as predation or human activities like fishing and shipping.

Ocean acidification

The increased absorption of carbon dioxide by the ocean leads to ocean acidification, which can have adverse effects on marine ecosystems. Acidification can negatively impact the base of the food chain, including phytoplankton and other organisms that krill rely on for sustenance. This disruption can ultimately affect seal populations that depend on krill and other affected species as a primary food source.

Overall, the impacts of climate change on Antarctica and Antarctic seals pose significant challenges for the long-term survival of these species and the health of the entire Antarctic ecosystem. Continued research and monitoring are essential to better understand these impacts and develop effective conservation strategies to protect Antarctica’s unique marine life.

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