Elephant seals are marine mammals known for their ability to navigate the ocean’s depths. They spend a significant portion of their lives far below the surface, accessing resources and evading dangers. Their deep-diving capabilities highlight their adaptation and survival in challenging environments.
Unveiling Their Deep Dive Records
Elephant seals are among the deepest diving non-cetacean mammals. Southern elephant seals have been recorded reaching a maximum depth of 2,388 meters (approximately 7,835 feet), while northern elephant seals can dive to at least 1,735 meters (around 5,692 feet). On average, they typically dive to depths ranging from 300 to 600 meters (about 1,000 to 2,000 feet).
These dives are also long in duration. Females generally spend about 20 minutes underwater per dive, while males can extend their dives to around 60 minutes. Some individual dives have been observed lasting up to two hours. Elephant seals spend approximately 90% of their time at sea submerged, making repetitive dives with brief surface intervals, typically lasting just two to three minutes.
Biological Adaptations for Extreme Depths
Elephant seals possess physiological adaptations that enable deep-diving and tolerance to immense pressure. One adaptation involves their respiratory system; they exhale almost all air from their lungs before diving. This reduces buoyancy for easier descent and helps prevent decompression sickness by minimizing nitrogen absorption, as their lungs and rib cage collapse under pressure, forcing residual air into reinforced airways.
Their circulatory system is specialized for oxygen storage and management. Elephant seals have a larger blood volume compared to terrestrial mammals, making up about 20-22% of their body weight, compared to approximately 8% in humans. Their blood is rich in hemoglobin, and their muscles contain high concentrations of myoglobin, both proteins that bind and store oxygen efficiently.
During a dive, their heart rate slows, a phenomenon known as bradycardia, decreasing from a surface rate of 80-110 beats per minute to as low as 3-15 beats per minute. Blood flow is shunted away from less critical areas like the extremities to prioritize vital organs such as the brain and heart. These adaptations allow them to tolerate low blood oxygen levels, utilizing nearly all available oxygen stores during underwater excursions.
The Purpose Behind Their Deep Dives
Elephant seals undertake deep dives primarily for foraging, seeking prey in the deeper parts of the ocean. Their diet consists mainly of deep-dwelling squid, various fish species, rays, and small sharks. By accessing these deeper zones, they exploit food sources unavailable to many other marine predators. This strategy also reduces competition for food in shallower waters.
Another reason for their deep-diving behavior is to avoid surface predators. Killer whales and large sharks, common threats to seals, typically hunt in shallower waters. Descending to great depths provides a refuge from these dangers. Elephant seals can also engage in brief periods of sleep while submerged, either by sinking slowly or resting on the seabed, using deep water as a safe haven during their time at sea.