Spatial–Temporal Distribution of Megamouth Shark, Megachasma pelagios, Inferred from over 250 Individuals Recorded in the Three Oceans

Abstract

The megamouth shark (Megachasma pelagios) is one of the rarest shark species in the three oceans, and its biological and fishery information is still very limited. A total of 261 landing/stranding records were examined, including 132 females, 87 males, and 42 sex unknown individuals, to provide the most detailed information on global megamouth shark records, and the spatial–temporal distribution of M. pelagios was inferenced from these records. The vertical distribution of M. pelagios ranged 0–1203 m in depth, and immature individuals were mostly found in the waters shallower than 200 m. Mature individuals are not only able to dive deeper, but also move to higher latitude waters. The majority of M. pelagios are found in the western North Pacific Ocean (>5° N). The Indian and Atlantic Oceans are the potential nursery areas for this species, immature individuals are mainly found in Indonesia and Philippine waters. Large individuals tend to move towards higher latitude waters (>15° N) for foraging and growth from April to August. Sexual segregation of M. pelagios is found, females tend to move to higher latitude waters (>30° N) in the western North Pacific Ocean, but males may move across the North Pacific Ocean.

Allometric Growth of the Enigmatic Deep-Sea Megamouth Shark Megachasma pelagios Taylor, Compagno, and Struhsaker, 1983 (Lamniformes, Megachasmidae)

“…Currently, Megachasmidae is considered to be an early-diverging lineage located outside the Lamnidae + Cetorhinidae clade within the Lamniformes [6]. After description and naming by Taylor et al [1], more than 200 individuals of megamouth sharks have been reported to date [7]. Increasing…”

“…Currently, megamouth sharks are listed as "Least Concern" on the IUCN Red List. They can reach 7 m in body length [10,11] and are found at various depths, ranging from the surface to 1500 m [7,10,13]. A possible segregation among different ontogenetic stages or between sexes as well as seasonal migrations are also recognized [9,12].…”

“…Amorim et al [23] noted that despite some minor differences, the body proportion of a juvenile megamouth shark "agrees well" with that of adults, indicating an isometric growth; however, this has yet to be confirmed through morphometric analyses. Nakaya [8], Watanabe and Papastamatiou [11], and Yu et al [7] investigated the allometric relationships among multiple variables of different-sized megamouth sharks, but these studies only examined several basic variables (e.g., total length, body mass) and did not compare results to other species.…”

First record of the megamouth shark Megachasma pelagios (Lamniformes: Megachasmidae), from the United Republic of Tanzania

“…From 1976 to 2010 M. pelagios was considered rare, with only 50 individuals recorded globally during that time (Nakaya 2010). In recent years it is apparent that it is more common and widespread than previously thought, with 273 confirmed records to date across 16 countries in the Atlantic, Indian and Pacific Oceans (Yu et al 2021;Diez et al 2022;Skelton et al 2023). This species is classified as Least Concern on the IUCN Red List of Threatened Species, as it is globally distributed and does not appear to be heavily impacted by fisheries (Kyne et al 2019).…”

“…The species reaches a maximum total length (TL) of 820 cm, while size at birth is thought to be less than 170 cm TL (Ebert et al 2021), based on the smallest individual recorded to date (176.7 cm TL, from northern Sumatra, Indonesia) (White et al 2004). However, most individuals recorded to date have been between 400 and 500 cm TL (Yu et al 2021). Until August 2020, M. pelagios was primarily recorded from the Pacific Ocean (n = 214 in the western Pacific and n = 35 in the eastern Pacific) with just six specimens each from the Atlantic and Indian oceans (Yu et al 2021).…”