The ocean sunfish (Mola mola) is the world's largest known bony fish (sharks and rays are cartilaginous, not bony). At least one estimate over 3000 lb. has been recorded and individuals reaching 11 ft. (3 m.) from fin tip to fin tip have been seen. It is found in all oceans in tropical and temperate climes, and is known to eat gelatinous zooplankton (jellyfish) and probably small fishes and algae. In the eastern Pacific, Mola mola is normally found from British Columbia to South America, although in El Nino events it has been recorded as far north as Alaska.Ocean sunfish are native to the temperate and tropical waters of every ocean in the world.[8] Molagenotypes appear to vary widely between the AtlanticPacific, but genetic differences between individuals in the Northern and Southern Hemispheres are minimal.[18] and
Sunfish are pelagic and swim at depths of up to 591 metres (1,939 ft). Contrary to the general perception that sunfish spend much of their time basking at the surface, research suggests that adult M. mola actually spend a large portion of their lives submerged at depths greater than 200 metres (656.2 ft), occupying both the epipelagic and mesopelagic zones.[19] They stay in water warmer than 10 °C (50 °F) most of times.[19] In fact, prolonged periods spent in water at temperatures of 12° C (53 °F) or lower can lead to disorientation and eventual death.[16][18] Others point to sightings of the fish in colder waters such as those southwest of England outside of its usual habitat as evidence of increasing marine temperatures.[20] Researches theorize that the basking behavior at the surface may be a method of "thermally recharging" following dives into deeper, colder water.
Sunfish are usually found alone, but occasionally in pairs.[8] They swim primarily in open waters, but are sometimes seen near kelp beds taking advantage of resident populations of smaller fish which remove ectoparasites from their skin. Because sunfish must consume a large volume of prey, their presence in a given area may be used as an indicator of nutrient-rich waters where endangered species may be found.
Despite their size, ocean sunfish are docile, and pose no threat to human divers.[14] Areas where they are commonly found are popular destination for sport dives, and sunfish at some locations have reportedly become familiar with divers.[7] In fact, the fish is more threatening to boaters than swimmers, as its immense size and weight can cause significant damage when impacted by watercraft. Collisions with sunfish may cause damage to the hull of a boat,[24] and their bodies can become lodged in the propellers of larger ships.[25]
The flesh of the ocean sunfish is considered a delicacy in some regions, the largest markets being Taiwan and Japan. All parts of the sunfish are used in cuisine, from the fins to the internal organs.[10] Some parts of the fish are used in some areas of traditional medicine.[7]
Sunfish are accidentally but frequently caught in drift gillnet fisheries, making up nearly 30% of the total catch of the swordfish fishery employing drift gillnet in California.[9] The by-catch rate is even higher for the Mediterranean swordfish industry, with a 71% to 90% of total catch being sunfish.[10][23]
The fishery, bycatch and destruction of ocean sunfish is unregulated worldwide. In some areas, the fish are "finned" by fishermen who regard them as worthless bait thieves. This process, in which the fins are cut off, results in the eventual death of the fish, because it can no longer propel itself without its dorsal and anal fins.[26] The species is also threatened by floating trash such as plastic bags which resemble jellyfish, its main diet. Bags can choke and suffocate an individual or fill its stomach to the extent that it starves.[15]
Many areas of sunfish biology remain poorly understood, and various research efforts are underway, including aerial surveys of mola populations,[27] satellite surveillance using pop-off satellite tags,[27][10] genetic analysis of tissue samples,[10] and collection of amateur sighting data.[28] Recent studies indicate a decrease in sunfish populations that may be caused by more frequent bycatch and the increasing popularity of sunfish in human diet.[8]
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