Elephant seals are among the largest marine mammals. Their immense bulk is a defining characteristic, allowing them to navigate vast ocean distances and endure challenging conditions.
Understanding Elephant Seal Mass
Elephant seals exhibit significant weight differences between their two species and sexes, a phenomenon known as sexual dimorphism. Northern elephant seal males can weigh up to 3,700 kilograms (8,200 pounds) and measure up to 5 meters (16 feet) in length. Females are considerably smaller, weighing between 400 to 900 kilograms (880 to 1,980 pounds) and reaching lengths of up to 3.6 meters (11.8 feet), roughly one-third the mass of males.
Southern elephant seals are generally larger than their northern counterparts, making them the largest seals on the planet. Male southern elephant seals can range from 2,200 to 4,000 kilograms (4,900 to 8,800 pounds) and extend from 4.2 to 5.8 meters (14 to 19 feet) in length. Females of the southern species weigh between 400 to 900 kilograms (880 to 1,980 pounds) and are 2.6 to 3 meters (8.5 to 9.8 feet) long, showing an even greater size disparity between sexes.
Weight Fluctuations Across Life Stages
An elephant seal’s weight changes throughout its life, influenced by stages such as birth, growth, breeding, and molting. Newborn northern elephant seal pups weigh around 34 kilograms (75 pounds) and are about 1.2 meters (4 feet) in length. Southern elephant seal pups are born weighing 45 kilograms (100 pounds). Pups gain weight rapidly, with northern elephant seal pups gaining about 4.5 kilograms (10 pounds) per day during their one-month nursing period. Southern elephant seal pups can triple or even quadruple their birth weight within three weeks due to their mother’s fat-rich milk.
Adult elephant seals experience significant weight loss during their time ashore for breeding and molting, periods when they fast. Male elephant seals can fast for up to three months during the breeding season, losing around 40% of their body weight, which can be 900 kilograms (2,000 pounds). Females also fast while on land to give birth and nurse their pups, and again for molting. During the annual molt, adult female northern elephant seals can lose 25% of their body mass over about 40 days.
The Significance of Their Size
The immense size and thick blubber layer of elephant seals offer several biological advantages for survival in harsh marine environments. Blubber, a specialized fatty tissue, acts as an effective insulator, helping these animals maintain a stable internal body temperature in frigid ocean waters, which can be below 4.5°C (40°F) at foraging depths. This thick layer of fat, which can constitute nearly 50% of a male’s weight at the start of the breeding season, is also an energy reserve.
During extended fasting periods on land for breeding or molting, elephant seals metabolize their blubber for energy, nourishment, and water, as water is a byproduct of fat metabolism. This allows males to sustain themselves for up to three months during breeding without foraging, enabling them to maintain their mating advantages. The substantial body mass and blubber also play a role in their deep-diving capabilities, contributing to buoyancy control and pressure resistance at depths that can exceed 1,500 meters (5,000 feet). Their large blood volume and high oxygen storage capacity further support their ability to perform long, deep dives for foraging.