While on the beach at Kei Mouth on Saturday afternoon, 4 July 2020, we came across a very strange looking, badly decomposed carcass. We at first thought it may be the skeletal remains of a dolphin found a few days earlier, but on closer inspection realised that this was a skull of something else. When examining it with Dr Deborah Robertson-Andersson, we concluded, by it’s mouth and tooth structure that it was a filter-feeder, but were certain it was not a Whale Shark or Basking Shark, the two filter-feeding sharks that we know of.
We took a photograph to send to Dr Kevin Cole, Chief Scientist at the East London Museum. Home to the first Coelacanth recorded. Meeting Elise Haber a little later, she let us know that she had also seen the carcass, photographed it, and sent the photographs to Bryan Church, who in turn sent the photographs to Dr Cole.
When Dr Cole received the photographs, he requested that Bryan move the carcass up the beach and bury it to keep it safe. On Monday morning Dr Cole was in Kei mouth to inspect the carcass, take DNA samples and remove the skull for further examination. The carcass is very decomposed and one of the proposed species may be the the extremely rarely encountered Megamouth Shark (Megachasma pelagios). Full measurements could not be undertaken because of the decomposition. The species can thus not be confirmed until the results of DNA tests are available.
Dr Cole has taken samples to be sent for DNA testing. Should this turn out to be a Megamouth Shark, this would be Dr Cole’s second one! He recorded another specimen washed up in East London in 2009. There have only been 4 records of this species in South Africa, the first being in 2002.
The Megamouth has only been known to science since 1976, when it was captured by Hugh Gallagher on a U.S naval ship on 15 November 1976, in Oahu, Hawaii. It wasn’t until Leighton Taylor examined the 4.5-m, 750-kg specimen in 1983, that it was found it to be an entirely unknown type of shark, making it – along with the coelacanth – one of the more sensational discoveries in 20th-century ichthyology.
There are so few records of this species, that scientists keep a detailed record of every specimen caught or found washed up. As of 5 March 2018 there were only been 99 records of this shark.
The Ichthyology section of the Florida Museum of Natural History has documented 69 sighting records from 1976 to 2016. In addition, with recently added records from Taiwan (34 individuals) and Puerto Rico (one individual) (Hsu et al., 2015; Rodriguez-Ferrer et al., 2017), only 99 individuals have been officially recorded (a global sighting record list based on scientific literature is given in Table S1). (Liu, Joung, Hsu, Tsai, & Liu, 2018).
The Megamouth Shark (Megachasma pelagios) is a species of mid to possibly deep water shark. It is rarely seen by humans and is the smallest of the three living species of filter-feeding sharks alongside the whale shark and basking shark
As very little is known about this shark, scientists have had to speculate and conclude much about it from the little that is known.
By investigating the stomach contents of specimens and studying the mouth structure of the shark, scientists have been able to conclude that like the Whale(First image right) and Basking Sharks(Second image Right) it swims with its huge mouth wide open to allow as much water as possible to filter through to capture its prey that consists of small invertebrate animals called plankton, it is also known to eat jellyfish. (Taylor, Compagno, & Struhsaker, 1983). The shark’s mouth has a bright silvery lining, that has been suggested to be bioluminescent and used as a light trap to lure prey (FAO Species Catalogue, 1983). It has also been suggested that this could be used for individuals to identify each other. Neither of these theories have as yet been confirmed
The specimen found at Kei Mouth was very decomposed, making it impossible to get a positive identification without DNA testing. The Megamouth Shark is however said to have a very distinctive look.
It is said to be unmistakable with its extremely short but rounded snout, very large long head, huge mouth that extends behind the eyes. The mouth has many small hooked teeth and moderately long gills with gill rakers to capture prey. (FAO Species Catalogue, 1983)
The top of the body is described as grey or greyish-black, with the underside being white. (FAO Species Catalogue, 1983)
Although there is very little footage of the Megamouth Shark swimming, it is believed to be a relatively poor swimmer with a soft, flabby, stout body.
There is however a video of the shark that a diver was lucky enough to capture while swimming off the coast of Indonesia's Komodo Island.
Habits & Habitat
The Megamouth is believed to occur in the open ocean, Itabashi et al, 1997, say that the coloration and composition of its liver suggest this not to be a deep ocean species, but more of an epipelagic species, meaning that it would mostly be found from the sea surface to about 200m. Specimens have been recorded at depths from 5m to 166m.
An adult male shark that was captured alive in 1990, was fitted with a telemetric acoustic tag and tracked for 2 days. The data from the tracking devise showed that the shark followed a daily migration pattern.
The tagged shark would swim down to a depth of between 100m and 166m when is started to get light. It would stay at this depth for the day, then in the early evening, just before sunset it would swim up to a depth of 12m to 25 m and spend the night at this depth. It has been suggested that the megamouth shark may also follow vertical migrations of euphausiid prey during diel cycles. The telemetric track suggested that the shark was indeed somewhat less active than makos or basking sharks, but that it could sustain a slow rate of swimming for extended periods (FAO Species Catalogue, 1983).
There have been no records of pregnant females being captured. Observations of captured females, have led scientists to believe that this shark is viviparous, meaning the embryos will develop inside the female’s body, and the young are born live. Many shark species have this form of reproduction, which is accompanied by uterine cannibalism (FAO Species Catalogue, 1983).
From records of known specimens, scientists have been able to conclude that the Megamouth Shark can reach a length of at least 7m and weigh more than 770kg. Most of the specimens found have been sub-adults.
"This giant pelagic filter-feeding shark is perhaps the most spectacular discovery of a new shark in the twentieth century."
FAO Species Catalogue. (1983). Retrieved from FAO: http://www.fao.org/tempref/docrep/fao/009/x9293e/X9293E04.pdf
Liu, S., Joung, S., Hsu, H., Tsai, W., & Liu, K. (2018). Genetic diversity and connectivity of the megamouth shark (Megachasma pelagios). PeerJ, 4432.
Taylor, L. R., Compagno, L., & Struhsaker, P. J. (1983, July 07). Megachasma pelagios Taylor, Compagno & Struhsaker, 1983. Retrieved from Fishbase: http://www.fishbase.us/summary/SpeciesSummary.php?ID=5909&AT=megamouth+shark
Featured image - Monica Maroun
Head with spade - Bryan Church
Other images of decomposed body- Dr Kevin Cole
Whale Shark -Matthew T Rader
Basking Shark- Unknown
Megamouth in Philippines- Marine wildlife watch of the philippines