The Insane Biology of: The Elephant Seal

Southern elephant seals exhibit the most extreme sexual size dimorphism among Carnivora order members, surpassing wolves, tigers, grizzly bears, and polar bears in absolute mass.

Southern elephant seals rank as the deepest diving seals and second-deepest diving mammals overall, reaching depths recorded at 2,388 meters and remaining submerged for two hours—comparable to sperm whales and exceeded only by Cuvier’s beaked whales.

Elephant seals avoid decompression sickness—the “bends” afflicting human scuba divers—despite performing dives deeper and more frequent than conventional diving physiology models predicted possible for marine mammals.

Southern elephant seals were initially hypothesized to require anaerobic metabolism for their deepest and longest dives because scientists calculated that stored oxygen couldn’t sustain two-hour submersions aerobically.

Beach masters represent the approximately 1% of male Southern elephant seals responsible for 85-90% of successful inseminations, with top-ranking individuals potentially siring 500 pups across their lifetimes while most males never reproduce.

Male Southern elephant seals develop an elongated nasal appendage called a proboscis that distinguishes them from females and gives the species its common name, first described by Charles Darwin as reaching one foot in length when erected during breeding season.

Female Southern elephant seals exhibit strong natal philopatry, returning annually to their birth sites for breeding, while males establish territories at the same locations, creating predictable congregation points for reproduction.

Southern elephant seals undergo annual catastrophic molts where they simultaneously shed both fur and the entire upper cornified epidermal layer—an extreme process compared to gradual continuous shedding in humans or seasonal fur changes in other mammals.

Newly weaned Southern elephant seal pups face the highest mortality period of their lives, with only 30-40% surviving their first dive into the ocean, making Neil the seal’s successful development particularly remarkable given his rare Tasmanian weaning location 1,500 km from the nearest breeding colony.

Southern elephant seals exhibit strong natal philopatry, with individuals showing lifelong attachment to their birth locations, as demonstrated by Neil the seal repeatedly returning to Tasmania’s Salem Bay despite relocation attempts by conservation programs.

Southern elephant seals function as apex open ocean predators specializing in deep-water fish and squid, consuming 4.8 to 16 kg daily while spending approximately 90% of their time at sea when not breeding or molting.