Right whales sleep in an upright position.

Scientists have uncovered how the Mediterranean monk seal, known as Monachus monachus, can rest in an almost upright position in water, thanks to the release of gas bubbles. This unusual behavior during rest was first recorded by naturalists in 2008, and monk seals are the only known species of whales that rest in an upright position with their heads facing the surface. Researchers believe that staying directly beneath the surface allows them to sleep more peacefully because it protects them from waves while simultaneously avoiding additional energy expenditure required to descend to greater depths. How do they maintain this position? Until now, it has been unclear how they manage to stay in this position while seemingly sleeping. In a new study, scientists from the University of St Andrews in Scotland and the University of Neuchâtel in France discovered that monk seals release gas bubbles, which help them maintain a neutral position. Patrick Miller from the Marine Mammal Research Unit at the University of St Andrews explained that the main challenge is regulating the natural buoyancy of the animal, influenced by gases within its body. “Releasing air reduces the positive buoyancy of the animal, slowing its ascent to the surface,” he said. He added that monk seals initially start their descent into the depth where they will rest with their head pointing downward, but gradually turn so their head faces upward. “Once they assume an upright position, they still slowly rise toward the surface. This is prevented by releasing bubbles. Each released bubble slows their ascent and helps them remain just below the surface,” Miller said. Since they need to surface to breathe, each “rest dive” lasts around 20 minutes, and monk seals typically perform several such dives consecutively. How were these findings measured? Data for the study were collected using small devices attached to monk seals along the coast of Norway. The devices recorded sounds and three-dimensional movements of the animals, logging characteristic bubble sounds. Based on this data, scientists created a computer simulation that considered tissue density, water resistance, and the amount of gas in the animals' bodies. The simulation confirmed that releasing bubbles reduces the positive buoyancy of monk seals and enables them to remain submerged during rest. The research provides new insights into the unique adaptations of monk seals, highlighting their ability to conserve energy and ensure safety while resting in challenging aquatic environments. These findings contribute to a better understanding of marine mammal physiology and could inform future conservation efforts aimed at protecting these endangered creatures. The study underscores the importance of continued research into the behaviors and physiological mechanisms of marine mammals, offering valuable knowledge that can aid in their preservation. Scientists emphasize the need for further studies to explore other aspects of monk seal behavior and their ecological roles in marine ecosystems. The discovery adds to the growing body of scientific knowledge about the complex ways marine life interacts with its environment, revealing the intricate strategies animals employ to survive and thrive in underwater habitats. Researchers plan to conduct more fieldwork and simulations to refine their models and deepen their understanding of the factors influencing monk seal buoyancy and movement patterns. Future investigations may also examine how environmental changes, such as ocean temperature fluctuations and human activity, affect these behaviors. By continuing to monitor monk seal populations and their responses to external pressures, scientists hope to develop more effective measures to support their survival in increasingly dynamic marine environments.