The southern elephant seal (Mirounga leonina) is an apex predator that plays a key role in the ecological integrity of marine ecosystems. It is the largest seal in the world and is notable for being an extreme species in terms of its social structure, behavior, and physiology. It is notable for having the greatest size difference between males and females of any mammal, a phenomenon known as sexual dimorphism. Adult males, characterized by their prominent trunk, can reach a length of up to 5 meters and weigh up to 4 metric tons, while females measure up to 3 meters in length and weigh between 500 and 900 kilograms. Males maintain a strict dominance hierarchy during the breeding season: they defend harems that can consist of up to 130 females and manage to mate with most of them.
Elephant seals spend more than 90% of their lives at sea, where they undertake feeding migrations of more than 10,000 kilometers, traveling as far as 2,000 kilometers from the coast. Their dives are extraordinary; they can last between half an hour and 2 hours, separated by 2–3 minutes at the surface, and they descend to depths between 400 and 2,000 meters. Another part of their annual cycle takes place on land: breeding between September and November, and molting between December and April, during which they fast. The breeding season peaks during the first week of October. Each female gives birth to a single calf weighing approximately 44 kilograms, which she cares for and feeds for 21 days until it triples its weight. After this time, the females return to the sea to feed and regain the weight lost during lactation.
The species has a circumpolar distribution, with island populations in all the southern oceans. However, the coast of Chubut is home to its only continental breeding colony in a temperate latitude. The Atlantic coast of the Valdés Peninsula Protected Natural Area is the epicenter of the population, where 80% of the population is concentrated. Outside the protected area, elephant seals are distributed southward along approximately 100 kilometers of coastline, from Punta Ninfas to Dos Pozos.
Challenges
Historically, the southern elephant seal has faced the threat of interaction with large-scale commercial fisheries, which have negative impacts through entanglement in fishing gear or by potentially affecting the availability of its food. Furthermore, in coastal zones—particularly in unprotected areas south of the Valdés Peninsula—the animals are exposed to disturbances caused by off-road vehicle traffic and the proximity of tourists, visitors, and pets, which can affect their behavior and lead to consequences such as the abandonment of a calf if the mother feels threatened, or excessive energy expenditure during periods of fasting due to the need to move around.
Despite these threats, the Valdés population remained healthy and experienced sustained growth for more than 50 decades until 2022. In 2023, it was severely affected by an epidemic caused by the highly pathogenic avian influenza virus (H5N1), which killed 97% of the chicks and an unknown number of breeding adults. The census conducted in 2024 by WCS Argentina recorded a 61% decline in this population. According to a study published in 2025 by WCS Argentina, CONICET, and the University of California, Davis, it will take decades for the population to recover; it could take three human generations—provided there are no further impacts—before these animals are as healthy and numerous as they were before the epidemic. In 2026, the species’ global conservation status changed from “Least Concern” to “Vulnerable,” according to the criteria of the International Union for Conservation of Nature (IUCN).
Our Work
Conservation strategies for this species must address not only the threats along the coast where they breed but also those in their feeding areas, thereby covering both the terrestrial and marine stages of their life cycle. For this reason, since the 1980s, we have been conducting demographic studies of the Valdés Peninsula population, performing terrestrial counts throughout its coastal range during the breeding season. In recent years, we have also incorporated the use of drones for hard-to-reach areas. Additionally, we study the marine stages of the species using satellite technology and state-of-the-art instruments. This information is highly relevant not only for understanding their oceanic trajectories, feeding areas, and behavior, but also for obtaining fine-scale oceanographic data on the habitats they use.
Long-term, sustained research has allowed us to monitor changes in population abundance and distribution, analyze the factors driving these changes, and evaluate the effectiveness of conservation efforts. Thanks to our persistence in monitoring the species for more than 40 years, we can assess the effects of the unexpected avian influenza epidemic and model possible scenarios for population recovery.
At the same time, we have supported the creation of marine and coastal protected areas that benefit this species throughout Patagonia, and we seek to expand coastal protection beyond these protected areas through the management and regulation of activities, particularly during the breeding months. As part of these initiatives, we have placed awareness signs on beaches where elephant seals are exposed to human disturbance and supported the enactment of the provincial law for the protection of southern elephant seals in Chubut, passed in 2025, with the aim of defining strategies to protect critical habitats and areas essential to the species from human and environmental impacts.