It is always exciting to watch the footage collected from the Sharklife BRUVs (baited remote underwater video systems), however, it is made all that more exciting when the unknown appears. In November 2020, while watching some footage, Sharklife researchers came across a shark that they could not identify. Hoping for some help, the image was sent off to the Kwa-Zulu-Natal Sharks Board and within a few hours, we had a species name.
The shark was identified as Hemipristis elongata, more commonly known as a snaggletooth shark or fossil shark. Hemipristis elongata is a species of weasel shark, belonging to the family Hemigaleidae, and is the only living species in its genus Hemipristis. The word Hemipristis is the combination of two Greek words, “Half” and “Saw”. The names “half saw” and “snaggletooth” refer to the odd teeth that this shark has. The upper jaw of H. elongata contains sharp serrated teeth for cutting while the lower jaw has teeth that are long and curved for grasping. These teeth allow for H. elongata to have a diverse diet consisting of bony fish, crabs, stingrays, squid, octopus, and small sharks.
Figure 1. The teeth of H. elongata (snaggletooth shark). The top row is the teeth from the upper jaw, the bottom row is teeth from the lower jaw (Nakagawa, 2008).
Hemipristis elongata is a tropical shark known to occur in warm coastal waters throughout the Indo-West Pacific including the Red Sea, South Africa, Madagascar, Mozambique, Tanzania, India, Thailand, Indonesia, Vietnam, China, and Australia. It is usually encountered between 1 to 130m deep at the bottom of the water column.
Despite its wide distribution, H. elongata is naturally rare in most places it occurs. This made seeing it in Sodwana Bay a noteworthy moment as it is unlikely that it has ever been seen here before. Most records of this shark occurring in South Africa come from fisherman catch reports and accidental catches in shark nets.
Hemipristis elongata is a medium-sized shark, reaching a maximum total length of 2.4m, with a fairly slender body and curved pectoral and pelvic fins. The snout is moderately long and broadly rounded with a long mouth and strong jaws. The coloring of H. elongata can vary from light grey to bronze with no prominent markings on their body except for light tips on their pectoral and pelvic fins. Hemipristis elongata has a seasonal reproductive cycle and uses a reproduction method known as viviparity with a yolk-sac placenta. After a gestation period of seven to eight months, these sharks give birth to between 2-11 live young per litter which ranges between 45-52cm at birth.
Figure 2. The distribution of H. elongata across the Indo-West Pacific. (White & Simpfendorfer, 2016)
Due to these sharks being naturally rare across their distribution range, there is currently little information on their population size and structure, but the population is assumed to be declining and has been listed a vulnerable to extinction by the IUCN. This is because the high quality of flesh, fins, and liver of H. elongata make them a target of many unmanaged and intensive coastal fisheries and while they are thought to have a high ability to sustain fishing due to their rapid growth and maturity, market surveys have shown that they are decreasing.
Hopefully, more can be learned about this species in the near future and that action will be taken soon to ensure that the fisheries of H. elongata are made sustainable to ensure that this species does not join the other species in its genus and become permanently known as a fossil shark.
References:
Compangno, L.J.. 1984. FAO fisheries synopsis no. 125. In: FAO species cata- logue. vol. 4. Sharks of the world. An annotated and illustrated catalog of shark species known to date. Part 2: Carcharhiniformes. Rome.
Compangno, L.J.. 1999. An overview of Chondrichthyan systematics and biodiversity in southern Africa. Transactions of the Royal Society of South Africa. 54(1):75–120.
Jaiteh, V.F. & Momigliano, P. 2015. New distribution records of the Vulnerable fossil shark Hemipristis elongata from eastern Indonesia call for improved fisheries management. Marine Biodiversity Records. 8:1–5. DOI: 10.1017/S1755267215000548.
Nakagawa, F. 2008. Snaggletooth shark. Available: http://naka.na.coocan.jp/discussion2e.html [2021, February 22].
White, W.. & Simpfendorfer, C. 2016. Hemipristis elongata. 8235.
White, W.. & Simplfendorfer, C. 2019. Fossil Shark , Hemipristis elongata.
Written By Jessica Arro
