Whale breaching, the dramatic display of a cetacean leaping clear of the ocean surface, is one of the most powerful and recognizable marine behaviors. This leap, where a whale propels a significant portion of its body into the air, is a frequent topic of inquiry. Scientists often ask whether this energetic activity continues once the sun sets and the ocean is cloaked in darkness. Understanding the timing requires looking closely at the substantial effort involved and the underlying motivations for the behavior.
The Mechanics and Purpose of Breaching
Breaching demands a tremendous amount of physical power. To successfully clear the water, a humpback whale must accelerate rapidly, reaching speeds between 6.2 and 8.2 meters per second. This maneuver is metabolically costly, expending up to 2.3% of the whale’s entire daily energy budget. The energy required for one full breach is comparable to a 60-kilogram human running a marathon.
Given this energy expenditure, scientists believe breaching serves several biological functions. The forceful impact with the water dislodges external parasites, such as barnacles and whale lice. Breaching is also a form of long-distance communication, with the loud splash acting as an acoustic signal that travels clearly through the water. Additionally, repeated breaching may serve as exercise, helping young whales develop myoglobin stores to improve their diving ability.
Nocturnal Versus Diurnal Activity Patterns
Whales do breach at night, but the frequency is lower than during daylight hours. This reduction is tied to the motivation behind the behavior, which shifts with the absence of light. Behaviors intended for visual communication, such as dominance displays or courtship rituals, are less effective in darkness. Therefore, social-related breaching tends to follow a strong diurnal pattern.
Activity patterns for many whale species reveal a change in vertical movement after sunset. Humpback, fin, and blue whales often exhibit shallower diving behavior at night, spending more time closer to the surface. This nocturnal shift is frequently linked to following the vertical migration of their prey. While whales spend more time near the surface, breaching may be less necessary for visual signaling, though acoustic communication and parasite removal can still occur.
Observing Whale Behavior in Darkness
Studying surface activity like breaching after dark presents a significant challenge for scientists who traditionally rely on visual observation. Researchers overcome this limitation by deploying advanced technologies that record data continuously, regardless of light conditions.
Suction-Cup Tags (DTAGs)
One primary tool is the suction-cup tag, or DTAG, which is temporarily affixed to the whale’s body. These tags contain three-axis accelerometers and pressure sensors. They record the massive, sudden acceleration required for a breach, providing quantitative data on the event’s trajectory and force.
Passive Acoustic Monitoring
Passive acoustic monitoring is another valuable method, employing arrays of hydrophones to listen for the loud splash sound characteristic of a breach. Although hydrophones are more often used to track the whales’ vocalizations, they can detect surface-active behaviors like breaching and tail-slapping across vast areas, 24 hours a day.
Thermal Imaging
Thermal imaging cameras, often mounted on research vessels or land stations, are used to detect the warm exhalation, or blow, of a whale against the colder ocean background. This technique allows scientists to visually confirm the presence of a whale at the surface in total darkness, confirming that surface activity is not strictly confined to the day.