Leopard Seals Frequently Target Southern Right Whales, Threatening the Recovery of This Endangered Species.
Every year, thousands of Southern Right Whales migrate to the calm waters of the Valdés Peninsula off the coast of Argentina to mate and give birth. These marine mammals, which can reach lengths of up to 17 meters, create an impressive spectacle, especially with their calves swimming closely behind. However, over the past 50 years, leopard seals in the Valdés Peninsula have routinely attacked any Southern Right Whale that surfaces to breathe, feeding on the skin and blubber ripped from the whales’ backs. Recent studies published on June 7 in the journal Biology Letters indicate that this issue has escalated to the point where young Southern Right Whales are dying prematurely.
Leopard seals attacking Southern Right Whales. (Photo: Rodrigo A. Martínez Calatalán).
While leopard seals and many other seabirds occasionally consume fresh flesh (even eyeballs) from marine mammals, the study found that the number of young Southern Right Whales dying before their first birthday has increased over the past few decades, along with the frequency and severity of the injuries inflicted by the seals. According to Macarena Agrelo, a marine ecologist at the Federal University of Santa Catarina in Brazil and co-author of the study, this is a troubling reality.
Although Southern Right Whales and leopard seals have coexisted for a long time, their relationship became peculiar in the 1970s. Prior to that, the seals seemed satisfied with eating naturally molted whale skin. Somehow, they discovered that they could secure better meals by targeting the living whales directly. Since then, this knowledge has been passed down from generation to generation.
“The attacks are very painful and cause extensive, deep injuries, especially on the backs of the calves,” said Mariano Sironi, scientific director at the Argentine Whale Conservation Institute. “While some of the wounds are fairly small, in most cases, the largest injuries cover a wide area on the back of the young whales, measuring a meter or more in length.”
Initially, the seals attacked both calves and adult whales, but over time, adult whales adjusted their surfacing behavior, curving their backs so that only their heads protruded. Calves cannot do this. The frequent attacks by leopard seals not only inflict painful injuries on young Southern Right Whales but also affect their ability to rest. Combined with other pressures, this leads to early mortality among the calves.
After analyzing thousands of aerial observations and images collected from 1970 to 2017, the research team found that the number of injured juvenile Southern Right Whales in the Valdés Peninsula increased tenfold over two decades. During this same period, they correlated the decline in survival rates of calves with the severe injuries caused by the seals.
Once on the brink of extinction, Southern Right Whales have been recovering since the hunting ban in 1935. However, like all whale species today, their recovery is threatened by food availability, entanglement in nets, and collisions with boats. Additionally, leopard seals contribute to these challenges.
