The ocean sunfish, Mola mola, is one of the largest bony fish in the marine world. Its unusual appearance, a large, flattened head with prominent dorsal and anal fins, propels it through the water. Its Latin name, “mola,” means “millstone” due to its round form.
Adults typically weigh between 247 and 1,000 kilograms (545 to 2,205 pounds) and grow up to 3.3 meters (10 feet 10 inches) in height. They are the heaviest bony fish known. Their thick, leathery skin ranges in color from brown to silvery-grey or white.
Global Distribution
Ocean sunfish are widely distributed across the globe, inhabiting both temperate and tropical oceans. Their range includes the Atlantic, Pacific, and Indian Oceans, allowing them to be found from colder temperate to warmer tropical waters.
They undertake long-distance migrations across ocean basins. Their presence across a wide latitudinal spread indicates significant movement, and they are found in all major oceans. They are often observed in areas like the Mediterranean Sea and the North Sea, demonstrating their expansive distribution.
Preferred Habitat Conditions
Within their vast global range, Mola mola primarily inhabits pelagic, or open ocean, waters. This preference means they spend most of their lives away from coastal shores, navigating the expansive blue water environments. They can be found in depths ranging from the surface down to several hundred meters, with some documented sightings as deep as 480 meters (about 1,575 feet) or even 1515 meters (about 4,970 feet).
While they are largely open-ocean dwellers, ocean sunfish are occasionally observed closer to coastal areas. These visits often occur for specific purposes, such as “sun basking” near the surface or utilizing “cleaning stations” where smaller fish remove parasites from their skin. These behaviors allow them to maintain their health and regulate body temperature.
Ocean sunfish prefer waters with temperatures typically ranging between 12°C and 25°C (53.6°F and 77°F). They often come to the surface to warm themselves, a behavior from which they derive their common name, “sunfish.” This thermoregulation allows them to then dive into cooler, deeper waters for foraging, showcasing their ability to navigate different thermal layers of the ocean.
Threats to Their Habitat
The habitats of ocean sunfish face several environmental challenges. One significant threat is bycatch, where Mola mola are unintentionally caught in fishing gear designed for other species. Their large size and presence in active fishing grounds increase their vulnerability to entanglement in nets and lines.
Ocean pollution, particularly plastic debris, also poses a risk to these creatures. Sunfish can mistakenly ingest plastic bags or other floating waste, mistaking them for their primary prey, such as jellyfish. This ingestion can lead to internal injuries or blockages, affecting their ability to feed and survive. The increasing amount of plastic in marine environments directly impacts their feeding grounds.
Climate change presents another potential long-term threat to Mola mola habitat. Changes in ocean temperatures could alter the distribution of their preferred prey, such as jellyfish and other gelatinous zooplankton. Shifts in ocean currents and thermal stratification due to climate change may also impact their migratory patterns and foraging efficiency, influencing the overall suitability of their living spaces.