Mudjekeewis D. Santos2
,
Jade Tiffany S. Rey2
,
Princess Ann P. Tayag3,
Clien Yvan A. Ongkiatco4
Marine Wildlife Watch of the Philippines, Barangay San Isidro, Makati City, 1234 Metro Manila, Philippines
Corresponding author
aayaptinchay@mwwphilippines.org
Megachasma pelagios, commonly known as the megamouth shark, is the lone extant shark species belonging to the family Megachasmidae and genus Megachasma. It was first described in 1978 by Taylor et al. (1983), with fewer than three hundred specimens recorded to date. Given its rarity and elusiveness, no pregnant or neonate megamouth sharks have ever been documented. On 14 November 2023, a freshly dead adult female megamouth shark carrying seven pups washed up on the shores of Barangay Ipil, Dipaculao, Aurora, Luzon Island, Philippines. This event has confirmed that megamouth sharks are ovoviviparous. Here, we establish the identity of the specimens using morphological and molecular methods and identify their morphometric differences through allometric analysis. Morphological identification was performed using available photo documentation and morphometric data, with results compared with published literature. On the other hand, the mitochondrial cytochrome c oxidase subunit 1 (MT-COI) gene was used for molecular identification. A phylogenetic tree was constructed using the Kimura two-parameter (K2P) model with 1000 bootstrap replicates. Allometric analysis was investigated using linear regression of each of the 19 morphometric trait measures against the total body length of the specimens. Based on morphological and molecular evidence, the results confirmed the identity of the stranded sharks as M. pelagios. Furthermore, morphological scaling of the mother vis-à-vis pups revealed that while some traits scale isometrically, the presence of negative and positive allometry in most traits indicates that the offspring are not completely isometric with the mother. Thus, it implies that the pups are morphologically distinct from the mother. Overall, this study provides a definitive identification of the stranded megamouth sharks, and the allometric measurements show new information on the basic biology of this rare fish species.