Basking sharks, the world’s second-largest fish, are known for their gentle, slow-moving nature as they filter-feed on microscopic plankton near the ocean’s surface. Despite their calm demeanor, these massive creatures exhibit a surprising and powerful behavior: breaching. This sudden, explosive leap offers a contrast to their usual movements, highlighting an unexpected athletic capability.
Understanding Basking Shark Breaching
Basking shark breaching involves these enormous animals propelling nearly their entire bodies out of the water. This impressive act often concludes with a significant splash as they re-enter the surface. Studies indicate these sharks can achieve vertical speeds comparable to the great white shark, around 5 meters per second. Unlike white sharks, which often breach during prey pursuit, basking sharks perform this feat from shallower depths, around 20 meters. This powerful ascent often involves rotation, with many individuals rolling to their right side during the breach.
Basking sharks sometimes breach multiple times in quick succession; one individual was recorded performing four breaches within 47 seconds. This behavior occurs both day and night, with a peak in activity around 4 AM. The power required for such a large animal, reaching lengths of up to 11 meters and weighing over 5,000 kg, to launch itself airborne is considerable, consuming significant mechanical energy. An 8-meter shark, for instance, might expend 63–72 kilojoules for a single breach.
Reasons for Breaching Behavior
The reasons why basking sharks breach remain a subject of scientific study, with several hypotheses explored for this energetically costly behavior. One theory suggests breaching could serve as a method for removing parasites or commensals from their skin. However, research involving tagged sharks indicates that common parasites like lampreys were not dislodged during breaching events, making this reason less likely.
Another hypothesis centers on communication among sharks. Breaching could function as a visual signal or, more likely given that breaches occur day and night, an acoustic signal that travels far underwater. The loud impact of a large shark hitting the water could communicate with other individuals, potentially for social interactions or to reunite with a group. This aligns with observations of basking sharks forming aggregations, particularly during summer months.
Breaching may also play a role in courtship or mating displays. While little is definitively known about basking shark mating behaviors, close following and breaching have been observed in areas like Scottish waters where mating events are thought to occur. The behavior could signal a shark’s readiness to mate or be part of a display of strength and size to attract potential partners. Breaching could also be a form of play or related to prey aggregation, though these are less explored possibilities.
When and Where Breaching Occurs
Observing a basking shark breaching is rare due to its infrequent occurrence. This behavior is most commonly witnessed during the summer months when basking sharks gather in areas with dense zooplankton concentrations. These aggregations often lead to increased social interactions, including breaching.
Hotspots for observing basking shark breaching include coastal waters around the United Kingdom and Ireland. The Sea of the Hebrides off the west coast of Scotland is an area where breaches are frequently reported. In Ireland, sightings are common along the south coast, from Cork to Kerry, and on the north coast in Mayo, Sligo, and Donegal. Witnessing a breach remains a special sight.