INTRODUCTION
The megamouth shark, Megachasma pelagios Taylor, Campagno & Struhsaker, Reference Taylor, Compagno and Struhsaker1983, is considered one of the most spectacular new shark discoveries of the late 20th Century. The discovery of such a large shark species, reaching over 5.5 m total length (TL), not only represented a new genus, but an entirely new shark family. The first capture of this pelagic shark species occurred in 1976, north-west of the Hawaiian Island of Oahu (21°51′N 157°46′W), but the species was not formally described for another seven years (Taylor et al., Reference Taylor, Compagno and Struhsaker1983). Since the capture of the first M. pelagios, an additional 64 specimens have been reported (Burgess, Reference Burgess2015a). The majority of records have come from the western North Pacific, particularly from off Japan (N = 16), the Philippines (N = 15) and Taiwan (N = 11), with an additional ten records from the eastern Pacific (Burgess, Reference Burgess2015b). Atlantic Ocean records are relatively sparse, with only three confirmed records, two from Brazil and one from off Senegal (Séret, Reference Séret1995; Amorim et al., Reference Amorim, Arfelli and Castro2000).
Indian Ocean records are limited to four widely scattered records; one from off South Africa and one each from off Western Australia, north of Sumatra and the high seas of the East Indian Ocean (Berra & Hutchinson, Reference Berra and Hutchinson1990; Smale et al., Reference Smale, Compagno and Human2002; White et al., Reference White, Fahmi and Sumadhiharga2004). The species may be captured incidentally more frequently, but, given its relatively low economic value is likely to be discarded at sea rather than returned to fish markets for sale. Furthermore, records of small juvenile specimens (<200 cm TL) are rare, since most specimens that have been reported are over 400 cm TL. Here we report on only the fifth known record of M. pelagios from the Indian Ocean – a small juvenile.
MATERIALS AND METHODS
An unusual shark landing was reported at Negombo fisheries harbour, Sri Lanka (7°12′11.67″N 79°49′44.35″E) on 5 July 2012. The shark was caught in a pelagic gillnet at night by a commercial multi-day fishing vessel operating out of Negombo. Anecdotal information from the boat captain revealed that the specimen was captured while fishing within the Sri Lankan Economic Exclusive Zone (EEZ) and in relative close proximity to the coast (<92 km offshore). This would place the catch location off the continental shelf in water depths ranging from approximately 2300 to 2600 m. The fishermen had brought the specimen back since they had never encountered one before, but discarded it into the Negombo lagoon after displaying it for a few hours at the market.
RESULTS
Upon examination of photographs received from fishers (Figure 1), the specimen was identified as a megamouth shark, Megachasma pelagios (Taylor et al., Reference Taylor, Compagno and Struhsaker1983), making it the first record of this species within Sri Lankan waters, and the first known record from the northern Central Indian Ocean. This specimen was estimated to be around 180 cm TL, a small juvenile, but the sex could not be determined from the photographs.
Megachasma pelagios Taylor, Campagno & Struhsaker Reference Taylor, Compagno and Struhsaker1983, juvenile: (A) dorsal view; (B) right lateral view.
DISCUSSION
This record of Megachasma pelagios, the first in northern Central Indian Ocean, is important in understanding the wide geographic range and ecology of this species. Records of small juvenile M. pelagios, measuring less than 2 m TL, are extremely rare with only two previously confirmed records and all other records being of adults and sub adults (Séret, Reference Séret1995; Amorim et al., Reference Amorim, Arfelli and Castro2000; White et al., Reference White, Fahmi and Sumadhiharga2004). The birth size of M. pelagios is estimated at below 170 cm TL (Ebert et al., Reference Ebert, Fowler and Compagno2013), with the smallest specimen on record being a juvenile male of 176.7 cm TL found stranded in Sumatra, Indonesia (White et al., Reference White, Fahmi and Sumadhiharga2004). Adult M. pelagios are estimated to reach sexual maturity at around 4.5 m TL for males and over 5.5 m TL for females (Ebert et al., Reference Ebert, Fowler and Compagno2013); maximum length is estimated at about 7 m TL.
Recently, the Food and Agriculture Organization (FAO) has initiated a program to assist in the identification of pelagic sharks and rays in the Western Indian Ocean (FAO, 2014). The program is designed to improve the identification of pelagic sharks and rays that are of major, moderate or minor importance. Species such as M. pelagios are among those little known species that the program aims to alert fishers about and to record their occurrence should they encounter this and other little known species.
The capture in a pelagic gillnet of M. pelagios off the continental shelf further supports other records of this species as preferring a pelagic habitat. Capture at night is also consistent with other records and can be attributed to the diel vertical migration of this species; ascending to upper layers at night and descending by day (Nelson et al., Reference Nelson, Mckibben, Strong, Lowe, Sisneros, Schroeder and Lavenberg1997; Ebert et al., Reference Ebert, Fowler and Compagno2013). The widespread records of M. pelagios from around the Indian Ocean, and elsewhere, indicates that this species is fairly wide-ranging and may be encountered more frequently than previously thought in pelagic fisheries. Improved species identification products for fishers such as those available through the FAO will be invaluable to refining species-specific catch information. The information gathered may eventually provide a useful resource for learning more about the life history and ecology of little known species such as M. pelagios. The occurrence of M. pelagios in Sri Lankan EEZ waters brings the number of shark species known to occur here to 61 (De Silva, Reference De Silva2015).
ACKNOWLEDGEMENTS
We are grateful to J. Fernando of Negombo, Sri Lanka for informing us about this unusual landing and for providing photographs for publication. This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
