The Megamouth Shark: Gentle Giant of the Deep
By Dave van Beuningen, Rhett Bennett, and Abdalla Abdulla
March 13, 2024
Sharks and rays are among the most threatened animals on the planet (with over 32 percent of the approximately 1200 species globally now threatened with extinction). This imperilled group of animals has thus become a core focus for WCS (Wildlife Conservation Society).
In the United Republic of Tanzania, which includes mainland Tanzania and the islands of Pemba and Unguja that together form the Zanzibar Archipelago, fisheries are predominantly artisanal and sharks and rays have been targeted for centuries. Although sometimes caught as bycatch, sharks and rays are commonly targeted using gear types like handlines, longlines, and bottom-set gillnets (known locally as ‘jarife’). Shark and ray meat is a relatively cheap staple food in Tanzania, and shark liver oil can be used to maintain traditional wooden boats.
Although the megamouth shark grows to an impressive 8 metres (26 feet) in length and has an enormous, gaping mouth, only around 270 have ever been recorded.
Since 2017, WCS has been monitoring coastal shark and ray landings and trade, through surveys at landing sites and fish markets in mainland Tanzania and Zanzibar, to obtain information for improved conservation and management. These surveys have recorded at least 44 shark and 28 ray species landed. That includes one very unusual shark species rarely seen globally, and less so in the Indian Ocean: the megamouth shark.
Megamouth sharks are fascinating creatures that have captured the curiosity of humans since their discovery off Hawaii in 1976. Although they grow to an impressive 8 m (26 ft) in length and have an enormous, gaping mouth reaching up to 1.3 metres (4 feet) in width, their rare sightings by people (only around 270 have ever been recorded) have earned them a place among the most intriguing ocean dwellers, with much about this gentle giant still unknown.
Yet, its most remarkable feature is not its size, but its feeding method. Unlike most sharks who actively hunt their prey, the megamouth is a filter feeder — one of only three filter feeding sharks (the others being the whale shark and basking shark). This massive mouth is lined with hundreds of small, hook-shaped teeth that are used to filter feed on plankton, particularly krill.
Unlike most sharks who actively hunt their prey, the megamouth is a filter feeder — one of only three filter feeding sharks (the others being the whale shark and basking shark).
Studies suggest megamouth sharks migrate vertically with their prey, generally spending their days in the deep ocean and moving closer to the surface at night. Their large, black eyes and numerous sensory organs suggest they are well-adapted to the darkness of their deep-sea environment, where they can reach depths of around 1500 metres (~5000 feet).
To add to their intrigue, megamouth sharks may possess luminescent tissue in their mouths, which are believed to play a role in attracting prey. This adaptation showcases the incredible diversity of strategies that organisms have developed to survive in their respective environments.
On the 29th of July 2022, a male megamouth shark was recorded in Chole market on Pemba Island, Zanzibar, measuring approximately 170 cm in length, which is roughly their size at birth. The market vendor suggested that the specimen could be sold for 40,000 Tanzanian Shillings (approximately US$17), and that the meat would likely be sold for local consumption.
However, the most interesting finding is that this was the first ever record of a megamouth shark from the United Republic of Tanzania or anywhere along the East African coastline, and is only the 6th record of this species off the coast of Africa and the 8th anywhere in the Indian Ocean. Furthermore, Pemba Island is over 3,500 km from the closest previous record of this species, an individual recorded off the coast of South Africa, thus considerably increasing the information available on the global distribution range of this species.
This discovery in Tanzania emphasizes the fact that sharks and rays are an important socioeconomic resource in the country that needs sustainable management solutions.
This discovery in Tanzania emphasizes the fact that sharks and rays are an important socioeconomic resource in the country that needs sustainable management solutions. At the same time, it adds to the excitement surrounding these enigmatic creatures and highlights the ongoing exploration of our planet’s oceans and the potential for new information to be uncovered.
As we continue to explore the vast oceans, the megamouth shark serves as a reminder of the wonders that still await discovery. This elusive giant shark, with its gentle nature and remarkable adaptations, holds a special place in the marine world, alerting us again to the importance of preserving the delicate balance of life within our oceans.
Should you encounter a megamouth shark, please notify your nearest aquarium, university, or government fishery department, or contact the Wildlife Conservation Society.
Acknowledgements
The authors would like to thank the Shark Conservation Fund, a philanthropic collaborative pooling expertise and resources to meet the threats facing the world’s sharks and rays, who funded these surveys. The Shark Conservation Fund is a project of Rockefeller Philanthropy Advisors. The authors also acknowledge collaboration with the Ministry of Blue Economy and Fisheries of the Revolutionary Government of Zanzibar, and would like to thank Ame Sikiani Juma, who collected the data on this megamouth shark specimen.
A link to the paper can be found here, where it is freely downloadable: https://mapress.com/zt/article/view/zootaxa.5380.6.7
Dave van Beuningen is Associate Conservation Biologist of the Western Indian Ocean Shark and Ray Conservation Program at WCS.
Rhett Bennett is Program Manager of the Western Indian Ocean Shark and Ray Conservation Program at WCS.
Abdalla Abdulla is Marine Program Research Assistant at WCS Tanzania.
