Featured Species: Sicklefin Lemon Shark (Negaprion acutidens)

This week’s featured species comes to us from the Indo-Pacific and has skin the color the sun! Meet the Sicklefin Lemon Shark (Negaprion acutidens), kissing cousin of the more commonly known lemon shark (Negaoprion brevirostris). Both the sicklefin lemon and lemon sharks are in the family Carcharhinidae, which has over 59 species of medium to large bodied sharks. The sicklefin lemon shark typically reaches lengths of 8 to 10 feet (2.4 to 3 m) and weighs around 400 lbs (181 kg) (Parker, 2008). They are named both for their sickle-shaped trailing edged of their dorsal and pectoral fins, as well as their beautiful golden, lemon-like colored skin (Tricas et al., 1997).

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Okinawa Churani Aquarium (Photographer). (n.d.). Sicklefin Lemon Shark [Digital Image]. Retrieved from https://churaumi.okinawa/

The sicklefin lemon shark and the lemon shark share name of the same physical attributes. Both species have large, stocky bodies with relatively small eyes and moderately large gill slits (Ebert, Fowler, & Dando, 2015). Of course, both species are named such for their striking yellow-bronze skin, contrasted against white under bellies. Their first and second dorsal fins are relatively equal in size, an easily identifiable characteristic of the genus; however, the sicklefin lemon shark has dorsal, pectoral and anal fins that are more falcate, or sickle-shaped, than the lemon shark (Ebert, Fowler, & Dando, 2015). If the fin shape doesn’t seem pronounced enough for you to distinguish these two species from one another, don’t fret about being able to tell them apart on a dive. Your location will be enough! These two species do not overlap in their geographic ranges. The sicklefin lemon shark is found through the Indo-Pacific and eastern coast of Africa and the Red Sea. The lemon shark, on the other hand, is limited to the Atlantic Ocean, including the western coast of Africa and the Caribbean Sea and Gulf of Mexico, as well as a subpopulation along coastal regions of the western United States and South America.

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a. Bidet, J. (Photographer). (2015). N.acutidens in Maldives [Digital Image]. Retrieved from https://commons.wikimedia.org/ b. IUCN (Author). (2003). Geographic Range of N.acutidens [Digital Image]. Retrieved from https://www.iucnredlist.org/ c. Kok, A. (Photographer). (2009). N.brevirostris [Digital Image]. Retrieved from https://wikipedia.org/ d. IUCN (Author). (2015). Geographic Range of N.brevirostris [Digital Image]. Retrieved from https://www.iucnredlist.org/

Like their cousins, the sicklefin lemon shark has evolved to hunting and catching slippery prey items like bony reef fishes. The teeth in the upper and lower jaws are strongly differentiated. They have weakly developed serrations on the blades of the teeth in the upper jaws. While the teeth the in the lower jaws lack cusplets. These teeth are long with slightly hooked cusps, but no serrations. Each jaw contains 27 to 33 rows of teeth and can measure 4.6 feet (1.4 m) long (Parker, 2008). These teeth are ideal for grasping and pulling prey into the sicklefin lemon shark’s mouth whole.

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Fossilonline.com (Author). (n.d.). Sicklefin Lemon Shark Jaw [Digital Image]. Retrieved from https://fossilsonline.com/

The sicklefin lemon shark gives birth to live young through placental viviparity, meaning the young receive their nutrients from their mother through placental attachment during development in the womb (Pillans, 2003). Sicklefin lemon sharks typically give birth to 6 to 12 pups after a 10 to 11 month gestation period. Pregnant females choose to give birth in safe nursery habitats, such as mangroves, to give their pups the best chance of survival. Following parturition, the little pups are fully fledged hunters who will spend their first few years honing their skills in the relative safety of their nursery habitats. Their mothers return to deep waters and will be ready for another reproductive cycle the following year. During the mating season, a male sicklefin lemon shark will express his interest in a receptive female by tailing behind her (Mourier, Buray, Schultz, Clua, & Planes, 2013). As far as courtship behaviors go, it may not be the most flashy, and it may be a little stalkerish, but is gets the job done. The act of mating itself is often violent for the female, with the male biting onto the female’s gills or pectoral fins to position himself to insert his clasper and deliver his biological package.

PLOSMedia [Videographer]. (2013). Courtship behavior of the sicklefin lemon shark [Video Clip]. Retrieved from https://www.youtube.com/

 

Presently, the International Union for the Conservation of Nature classifies the sicklefin lemon shark as Vulnerable to extinction. Fishing pressures are high throughout their home range. Catch data from Australia suggests that the sicklefin lemon shark is taken in low quantities in gillnet and longlines fisheries, and the reported bycatch rates are also low (Pillans, 2003). However, offshore fisheries outside of Australia pose a higher risk, as they are caught in higher numbers in gillnets and longlines in southeast Asia. There is evidence to suggest we may already be seeing some local population extinctions in India Thailand, and they are very infrequent in Indonesia where historically they were more abundant. This suggests the sicklefin lemon shark is a species that is extremely susceptible to inshore fisheries and should be closely monitored for over-exploitation (Pillans, 2003). This species is also susceptible to local depletion due to its small home range and limited movements throughout its life (Stevens, 1984). The sicklefin lemon shark depend on specific nurseries year after year for pupping grounds and retain a particular home base throughout their life. Extensive coral reef destruction through pollution, mangrove deforestation, and dynamite fishing can threaten local populations with extinction (Pillans, 2003). At the time of this writing, there are no species specific conservation actions for the sicklefin lemon shark. However, populations should be monitored for exploitation and the influence of human activity should be closely considered on these sharks.

101Visions (Videographer). (2017). Dynamite Fishing [Video Clip]. Retrieved from https://youtube.com/

I’m delighted to announce a partnership with the wonderfully talented Julius Csotonyi! Julius creates stunning shark coloring sheets that are fun and educational for all ages. From time to time you’ll see Julius’ work featured right here and on my other social media platforms! You can find more coloring sheets in the store! You are welcomed to download these beautiful sheets and enjoy them with family and friends.

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Shark Stats

Authority: Rüppell, 1837

Family: Carcharhinidae, 59+ species

Length: 8 – 10 feet (2.4 – 3 m)

Weight: Up to 400 lbs (181 kg)

Habitat: Shallow coastal waters of coral reefs, keys, mangroves, bays and river mouths

Depth: Shallow waters to 300 ft (92 m)

Reproduction: Placental Viviparity

Gestation: 10 – 12 months

Litter Range: 4 – 17 pups

Home Range: Indo-Pacific Oceans

Diet: Bony fishes and crustaceans

IUCN Status: Vulnerable

(Tricas et al., 1997; Pillans, 2003; Parker, 2008)

The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Proceeds benefit shark research and conservation with a donation to Project AWARE!

Thanks so much for checking out the beautiful sicklefin lemon shark! If you missed last week’s featured species, please be sure to check out the deepwater Bigeye Sand Tiger Shark! If there is a species of elasmobranch you’d love to know more about, leave me a comment or send me a message! I would love to do a feature on your favorite species. Also connect with me on Instagram and Facebook for even more elasmo fun!

Conservation legislation needs public support in order to become law and help protect the environment and wildlife. Tell your representatives that you care about environmental and wildlife conservation. It only takes a moment to make a change that will last a lifetime. Until next time finactics!

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Featured Image Source

Quinn-Graham, P. (Photographer). (2009). Sicklefin lemon shark (Negaprion acutidens) in Sydney [Digital Image]. Retrieved from https://commons.wikimedia.org/

Literature Cited

Ebert, D. A., Fowler, S. L., & Dando, M. (2015). Sharks of the world: a fully illustrated guide. Wild Nature Press.

Mourier, J., Buray, N., Schultz, J. K., Clua, E., & Planes, S. (2013). Genetic network and breeding patterns of a sicklefin lemon shark (Negaprion acutidens) population in the Society Islands, French Polynesia. PLoS One8(8), e73899.

Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.

Pillans, R. (2003). Negaprion acutidensThe IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/41836/10576957

Stevens, J. D. (1984). Life-history and ecology of sharks at Aldabra Atoll, Indian Ocean. Proceedings of the Royal society of London. Series B. Biological sciences222(1226), 79-106.

Sundström, L.F. (2015). Negaprion brevirostris. The IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/39380/81769233

Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.

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Featured Species: Bigeye Sand Tiger Shark (Odontaspis noronhai)

 

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