The sperm whale, Physeter macrocephalus, is a remarkable predator of the deep ocean. As the largest toothed whale, its massive head, comprising up to one-third of its body length, houses specialized organs that facilitate its unique hunting strategy. Understanding its diet is central to comprehending its biology and impact on the marine ecosystem. Their specialized feeding habits allow them to thrive in an environment largely inaccessible to most other creatures.
Primary Prey
The diet of sperm whales primarily consists of various deep-sea cephalopods, with squid being the primary component. This includes smaller species, as well as the elusive giant squid (Architeuthis dux) and colossal squid (Mesonychoteuthis hamiltoni). Though direct observations of battles are rare, scars on whales’ heads suggest intense struggles during predation. A single sperm whale can consume between 400 and 800 squid per day, depending on the size of the prey.
Beyond squid, they supplement their diet with deep-sea fish, including demersal rays, skates, and various bony fish. Sharks, such as megamouth, sleeper, basking, blue, and mako sharks, have also been found in their stomachs. Their expansive throat allows them to swallow large sharks whole, a capability not shared by most other whale species. Despite this varied menu, the low energy content of squid necessitates consuming a substantial amount, around 3% to 3.5% of their body weight daily, totaling about one ton of prey.
Hunting Methods
Sperm whales use sophisticated techniques to locate and capture prey in the dark ocean depths. They primarily rely on powerful echolocation, a form of biosonar, to navigate and pinpoint targets. Sounds are generated by forcing air through a pair of phonic lips below the blowhole. This sound travels through the spermaceti organ, a large, waxy oil-filled structure in their head, before being reflected off a frontal sac and focused into a powerful beam by the melon.
Echoes from prey are received by the whale’s narrow lower jaw, which contains a fat-filled canal transmitting vibrations to the inner ear. As the whale closes in on prey, echolocation clicks increase in frequency, becoming a rapid series known as a “creak,” indicating the final phase of pursuit. Once prey is secured, often by gripping with their cone-shaped teeth, they are believed to use a “suction feeding” technique, creating a vacuum to draw the slippery prey into their mouths. Their teeth, while robust, are primarily for holding and not for chewing, as prey is swallowed whole.
Deep-Sea Habitat and Prey Location
Sperm whales hunt in the mesopelagic and bathypelagic zones of the ocean, also known as the twilight and midnight zones. These environments are characterized by darkness, immense pressure, and cold temperatures. Typical dives range from 300 to 800 meters and can last over an hour, though they can descend to over 2,000 meters for up to two hours. The pressure at these depths can be hundreds of times greater than at the surface, posing significant challenges for air-breathing mammals.
In this challenging environment, sperm whales navigate and locate prey using their specialized senses. Their echolocation system allows them to create an acoustic map, detecting the size and density of objects, including potential prey, from hundreds of meters away. While their eyesight is poor in comparison to humans, their eyes are adapted to detect faint blue light. Some researchers suggest bioluminescent organisms or light from their jaws might assist in prey detection. The availability of deep-sea squid and fish in these layers dictates their deep-diving and hunting behaviors.
Dietary Adaptations and Ecological Role
The sperm whale’s deep-sea predatory lifestyle is enabled by anatomical and physiological adaptations. The spermaceti organ, beyond its role in echolocation, assists in buoyancy regulation and pressure equalization during deep dives. By altering the temperature of the spermaceti oil, the whale can change its density, allowing for easier descent and ascent. Their flexible ribcage allows the lungs to collapse under pressure, preventing nitrogen from entering the bloodstream and mitigating the risk of decompression sickness.
Physiological adaptations include a high concentration of oxygen-storing proteins like myoglobin in their muscles and dense red blood cells to carry oxygen in their blood. During deep dives, they can lower their heart rate and direct oxygenated blood primarily to the brain and other essential organs. As apex predators, sperm whales play a significant role in the deep-sea food web by regulating populations of squid and deep-sea fish. Their consumption of prey at depth and defecation of nutrient-rich waste at the surface contribute to nutrient cycling, a process sometimes called the “whale pump,” which can stimulate phytoplankton growth and carbon removal from the atmosphere.