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

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.

First records of the megamouth shark Megachasma pelagios (Taylor, Compagno & Struhsaker, 1983) as bycatch in Peruvian small-scale net fisheries

Between October 2018 and October 2019, seven megamouth sharks were reported as bycatch in the small-scale surface and midwater gillnet fisheries operating from the ports of Mancora and Salaverry in northern Peru. Here we present details of these specimens and bycatch events that represent the first documented records of this species in Peruvian waters, confirming their occurrence as fisheries bycatch. We recommend continued monitoring programs in small-scale fisheries toward assessing the extent of this species’ occurrence in Peru and its vulnerability to fishery interactions.

The megamouth shark, Megachasma pelagios, is not a luminous species

Despite its five meters length, the megamouth shark (Megachasma pelagios Taylor, Compagno & Struhsaker, 1983) is one of the rarest big sharks known in the world (117 specimens observed and documented so far). This filter-feeding shark has been assumed to be a luminous species, using its species-specific white band to produce bioluminescence as a lure trap. Another hypothesis was the use of the white band reflectivity to attract prey or for social recognition purposes. However, no histological study has ever been performed to confirm these assumptions so far. Two hypotheses about the megamouth shark's luminescence arose: firstly, the light emission may be intrinsically or extrinsically produced by specific light organs (photophores) located either on the upper jaw white band or inside the mouth; secondly, the luminous appearance might be a consequence of the reflection of prey luminescence on the white band during feeding events. Aims of the study were to test these hypotheses by highlighting the potential presence of specific photophores responsible for bioluminescence and to reveal and analyze the presence of specialized light-reflective structures in and around the mouth of the shark. By using different histological approaches (histological sections, fluorescent in situ hybridization, scanning electron microscopy) and spectrophotometry, this study allows to unravel these hypotheses and strongly supports that the megamouth shark does not emit bioluminescence, but might rather reflect the light produced by bioluminescent planktonic preys, thanks to the denticles of the white band.

First reports of Megamouth Shark, Megachasma pelagios Taylor, Compagno & Struhsaker, 1983 (Lamniformes, Megachasmidae),& in Peru

Megamouth Shark, Megachasma pelagios Taylor, Compagno & Struhsaker, 1983, is one of the least-known shark species worldwide. We report the encounters of four megamouth sharks: one caught in a driftnet off Piura (November 2016; sex indeterminate), one landed in Los Organos (July 2018; female), one stranded in El Ñuro (July 2018; sex indeterminate, ca 300 m total length), and one caught in a purse seine off Lambayeque (June 2019; female, total length ca 300 cm). These are the first records from Peru and expand the species’ known southern limit by 415 km. With the addition of M. pelagios, there are 67 species of sharks in Peru.

A megamouth shark (Lamniformes: Megachasmidae) in the Burdigalian of Belgium

The enigmatic megamouth shark is a rare occurrence in both Recent oceans and in the fossil record. A temporary construction site in the city of Antwerp (NW Belgium) gave the opportunity to study the poorly known early Miocene Kiel Sand Member of the Berchem Formation. In this Burdigalian deposit, a previously unknown fossiliferous horizon with Glycymeris and Cyrtodaria was sampled which contained a single Megachasma tooth. This specimen, attributed to Megachasma aff. pelagios by its resemblance with extant M. pelagios, is the first in situ record from un-reworked strata in Belgium. Only around a dozen fossil Megachasma teeth have been reported from Europe. It is concluded that a circumglobal megamouth population existed during the Burdigalian. Some evolutionary remarks are made.

Genetic diversity and connectivity of the megamouth shark (Megachasma pelagios)

The megamouth shark (Megachasma pelagios) was described as a new species in 1983. Since then, only ca. 100 individuals have been observed or caught. Its horizontal migration, dispersal, and connectivity patterns are still unknown due to its rarity. Two genetic markers were used in this study to reveal its genetic diversity and connectivity pattern. This approach provides a proxy to indirectly measure gene flow between populations. Tissues from 27 megamouth sharks caught by drift nets off the Hualien coast (eastern Taiwan) were collected from 2013 to 2015. With two additional tissue samples from megamouths caught in Baja California, Mexico, and sequences obtained from GenBank, we were able to perform the first population genetic analyses of the megamouth shark. The mtDNA cox1 gene and a microsatellite (Loc 6) were sequenced and analyzed. Our results showed that there is no genetic structure in the megamouth shark, suggesting a possible panmictic population. Based on occurrence data, we also suggest that the Kuroshio region, including the Philippines, Taiwan, and Japan, may act as a passageway for megamouth sharks to reach their feeding grounds from April to August. Our results provide insights into the dispersal and connectivity of megamouth sharks. Future studies should focus on collecting more samples and conducting satellite tagging to better understand the global migration and connectivity pattern of the megamouth shark.