A devastating blow has struck the world's largest breeding colony of southern elephant seals, and the culprit is a highly pathogenic avian influenza virus (HPAIV). This crisis, unfolding on the remote island of South Georgia in the sub-Antarctic, has led to a nearly 50% decline in the breeding population of female seals, as reported by scientists in Communications Biology.
The researchers from the British Antarctic Survey in England warn that this loss could threaten the future of the population, especially considering the reduced number of surviving pups. It highlights the urgent need for continuous and intensive monitoring to understand the long-term effects of HPAIV on these magnificent creatures.
During the breeding seasons of 2022 and 2024, the team kept a close eye on the elephant seal populations at their breeding grounds on South Georgia, located in the South Atlantic Ocean. Using aerial imagery from three beaches, which represented a significant 15.6% of the island's colony based on the last population count in 1995, they witnessed a disturbing trend.
In 2024, the researchers estimated that approximately 53,000 female seals were absent from the population when compared to long-term average counts from 1958 to 2022. This represents a staggering 33.7% decline in the projected number of females, with a 47% decrease specifically among breeding females on those three beaches between 2022 and 2024.
South Georgia, along with the South Sandwich and Falkland Islands, is one of the four primary breeding grounds for the Mirounga leonina seal species in the Southern Ocean. As of 1995, it was home to around 54% of the global breeding population of these seals, making it a critical site for their survival.
The long-term impact of this population decline remains a mystery. However, the authors point out that HPAIV has caused mass mortalities in marine mammals and seabirds across South America, including a 67% drop in the female elephant seal population on Argentina's Valdes Peninsula.
The researchers suggest that the conditions during the 2023 breeding season, affected by HPAIV, could be to blame for the high number of pup deaths and abandonments, as well as deaths among adult males and females. While it is impossible to confirm that all absent females have perished, it is highly probable that a significant portion of them have succumbed to the virus.
After losing their pups or abandoning them due to their own HPAIV infections, female seals may have left the breeding colony beaches before the optimal time for reproduction, leading to reduced breeding opportunities. This could result in fewer pregnancies and, consequently, fewer females returning to give birth the following season.
Alternatively, the emergence of HPAIV could have caused some females to seek refuge in other colonies, dispersing the population and thus lowering counts at their usual beaches.
Additionally, an unusual sea-ice anomaly in the South Atlantic during the 2023/2024 austral winter may have influenced the distribution and foraging patterns of elephant seals, potentially impacting their recovery from HPAIV. However, given their wide-ranging movements and association with sea ice, the researchers believe that these localized conditions are unlikely to have had a significant impact on their recovery or altered their natural timing of events.
The long-term consequences of this population decline are unknown, but research on adjacent populations has shown that female survival is a critical factor in population growth.
"The future of this iconic species hangs in the balance, and we must act now to understand the full extent of this crisis." the researchers urge. "Follow-up monitoring in the coming years is crucial to distinguish between short-term fluctuations and enduring population-level impacts. With the increased availability of high-resolution satellite imagery, we have an opportunity to track these trajectories and make informed decisions to protect these seals."
And this is where you, the audience, come in. What are your thoughts on this devastating situation? Do you think enough is being done to monitor and protect these seals? Join the discussion in the comments and let's raise awareness together!
