Author: Bee Smith
Oceanic Whitetip Shark
Carcharhinus longimanus
The oceanic whitetip used to be one of the most abundant sharks in our ocean but is now critically endangered…
Key Features & Appearance
The oceanic whitetip shark has a unique appearance, with long pectoral and first dorsal fins that are rounded and have white mottling on the tips - from which it gets its name - and it is also white on its underside. This stunning shark has a maximum length of 3.5m (or possibly 3.95m) but typically is less than 3m.
Image Credit: Andy Murch
Habitat & Distribution
The oceanic whitetip occurs in all major fishing areas and in the waters around a large number of countries. It is mainly found offshore in the open ocean but can occasionally be found in coastal waters (usually around islands). It has a preference for surface waters, typically being found in the epipelagic zone from 0-200m, though it has been recorded going as far as 1,082m (so through the twilight and into the midnight zone). It is one of the most widespread sharks, being found in all oceans in tropical and subtropical waters between 30°N and 35°S, with its range crossing entire oceans. There is some evidence that there are distinct populations in different oceans and even within an ocean, such as between the Western and Eastern Atlantic Ocean.
Diet
The oceanic whitetip is a top predator. It primarily feeds on bony fish and pelagic cephalopods but is also known to predate on seabirds, marine mammals, other sharks and rays, as well as carrion.
Reproduction
The oceanic whitetip is thought to mate during the early summer months in the Northwest Atlantic and Southwest Indian oceans. It is generally solitary but is known to form congregations in certain locations which are hypothesised to be for mating, such as around Cat Island in the Bahamas. When these sharks come together they have been seen to do behaviours like nose to tail following, which has been linked to mating in basking and white sharks.
The oceanic whitetip only reaches sexual maturity at around 8 years old, or possibly only at 10-15 years, and from then reproduces every other year. It is viviparous, meaning that it gives birth to live young, and after a 10-12 month gestation period around 1-15 pups are born (with the number of pups correlating with the size of the mother). This slow reproduction means that the rate of population increase is very low.
Image Credit: Andy Murch
Threats
The oceanic whitetip was once one of the most abundant shark species in our oceans but it is now only occasionally reported. This is because it has experienced dramatic population declines in the last several decades due to overfishing. The shark's pelagic nature means it is tricky to study its population but it is known to have declined by as much as 95% or 99% in some regions, and is believed to have severely declined in all oceans due to similar fishing practices, with a global estimate of by 80-98%. The majority of the fishing pressure is bycatch in pelagic fisheries such as tuna and swordfish longlines, however due to the international fin trade they are often considered valuable bycatch and so are retained. Furthermore, even if the fishery does not plan to keep them for their fins there is evidence that oceanic whitetips often die on the lines, and if released alive they may also die later. In addition, they are subject to some targeted fishing for their fins as well as for their meat.
Though the oceanic whitetip has a reputation as one of the most dangerous sharks (thanks to Jacques Cousteau and the sinking of the USS Indianapolis…) it is clear that humans are the far more dangerous predator.
Team Member Candace Fields is Studying Oceanic Whitetip Sharks for her PhD Credit: John Carlson
Status
The oceanic whitetip is classified as “Critically Endangered” according to the International Union for Conservation of Nature (IUCN), and so urgent action is needed to start rebuilding the oceanic whitetip population.
Thankfully, the species has received some protection. For example, it is listed on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix 2 which controls the trade of its products, and there are now official catch and retention bans in all major tuna Regional Fishery Management Organization (RFMO)s, making it the first and only shark to receive this protection (though illegal trade and fishing does still occur).
Further action is required to save this species from extinction, namely to protect the remaining population in order to allow it to repopulate. For example, it is recommended that all oceanic whitetip retention and landings should be prohibited, there should be initiatives to minimise bycatch and also reduce bycatch mortality (e.g. by promoting safe release), and critical reproductive habitat should be protected (e.g. with area based management of fisheries). Due to its widespread, pelagic nature, saving this species is going to require international cooperation, as there is little use in protecting it in only one small portion of its habitat.
Fun Fact
An example of the oceanic whitetips' historical great abundance can be seen in the documentary “Blue Water, White Death”. This 1971 documentary inspired the making of Jaws and shows the journey of a film and dive crew (including Valerie & Ron Taylor!) on a mission to find a great white shark. Along the way they encounter other sharks and one scene shows them diving near a whale carcass to film a feeding frenzy of oceanic whitetips outside a cage. They establish their place in the pack using sticks and (despite the documentary later inspiring a film about a man-eating shark…) they demonstrated that sharks are not man-eaters, and humans could safely swim with them. This scene shows a great number of oceanic whitetips gathering, and you simply would not be able to see such a sight of abundance today. I would really recommend this documentary in general, but particularly this scene as it will inspire you to want to do everything you can to help sharks by showing you what we have already lost from our oceans.
Image Credit: The documentary “Blue Water, White Death” - it shows valerie taylor diving with oceanic whitetips
Works Cited
• Andrzejaczek, S., Gleiss, A.C., Jordan, L.K.B. et al. Temperature and the vertical movements of oceanic whitetip sharks, Carcharhinus longimanus. Sci Rep 8, 8351 (2018). https://doi.org/10.1038/s41598-018-26485-3
• Baum, J., Medina, E., Musick, J.A. & Smale, M. (2015). Carcharhinus longimanus. The IUCN Red List of Threatened Species 2015: e.T39374A85699641. http://dx.doi.org/10.2305/IUCN.UK.2015.RLTS.T39374A85699641.en.
• Camargo SM, Coelho R, Chapman D, Howey-Jordan L, Brooks EJ, Fernando D, et al. (2016) Structure and Genetic Variability of the Oceanic Whitetip Shark, Carcharhinus longimanus, Determined Using Mitochondrial DNA. PLoS ONE 11(5): e0155623. https://doi.org/10.1371/journal.pone.0155623
• Carcharhinus longimanus (no date) Discover Fishes. Available at: https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/carcharhinus-longimanus/ (Accessed: 07 September 2024).
• Cassandra L. Ruck. 2016. Global Genetic Connectivity and Diversity in a Shark of High Conservation Concern, the Oceanic Whitetip, Carcharhinus longimanus. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, . (412)
• D’Alberto Brooke M., Chin Andrew, Smart Jonathan J., Baje Leontine, White William T., Simpfendorfer Colin A. (2017) Age, growth and maturity of oceanic whitetip shark (Carcharhinus longimanus) from Papua New Guinea. Marine and Freshwater Research 68, 1118-1129.
• Gallagher, Austin & Romeiro, & Canabal, & Hammerschlag, Neil. (2014). Novel social behaviors in a threatened apex marine predator, the oceanic whitetip shark Carcharhinus longimanus. Ethology Ecology & Evolution. 26. 10.1080/03949370.2014.896831.
• Howey, Lucy & Brooks, Edward & Abercrombie, Debra & Jordan, Lance & Brooks, Annabelle & Williams, Sean & Gospodarczyk, Emily & Chapman, Demian. (2013). Complex Movements, Philopatry and Expanded Depth Range of a Severely Threatened Pelagic Shark, the Oceanic Whitetip (Carcharhinus longimanus) in the Western North Atlantic. PloS one. 8. e56588. 10.1371/journal.pone.0056588.
• Joung, S. J., Chen, N. F., Hsu, H. H., & Liu, K. M. (2016). Estimates of life history parameters of the oceanic whitetip shark, Carcharhinus longimanus, in the Western North Pacific Ocean. Marine Biology Research, 12(7), 758–768. https://doi.org/10.1080/17451000.2016.1203947
• Rigby, Cassie & Barreto, Rodrigo & Carlson, John & Fernando, Daniel & Fordham, Sonja & Francis, Malcolm & Herman, Katelyn & Jabado, Rima & Liu, Kwang-Ming & Marshall, Andrea & Pacoureau, Nathan & Romanov, Evgeny & Sherley, Richard & Winker, Henning. (2019). Carcharhinus longimanus-Oceanic Whitetip Shark. The IUCN Red List of Threatened Species 2019. 10.2305/IUCN.UK.2019-3.RLTS.T39374A2911619.en.
• Ruck, C.L., Shivji, M.S., Jabado, R.W. et al. Cross ocean-basin population genetic dynamics in a pelagic top predator of high conservation concern, the oceanic whitetip shark, Carcharhinus longimanus. Conserv Genet 25, 677–695 (2024). https://doi.org/10.1007/s10592-023-01596-1
• Scott, M., Royer, M. & Hutchinson, M. Time of death: behavioral responses of an oceanic whitetip shark, Carcharhinus longimanus, to capture by a longline fishing vessel. Anim Biotelemetry 11, 34 (2023). https://doi.org/10.1186/s40317-023-00346-x
• Tremblay-Boyer, Laura & Carvalho, Felipe & Neubauer, Philipp & Pilling, Graham. (2019). Stock assessment for oceanic whitetip shark in the Western and Central Pacific Ocean.
• Young, Chelsey & Carlson, John. (2020). The biology and conservation status of the oceanic whitetip shark (Carcharhinus longimanus) and future directions for recovery. Reviews in Fish Biology and Fisheries. 30. 10.1007/s11160-020-09601-3.
Images
Images of oceanic whitetip sharks taken by Andy Murch
Other image is from the documentary “Blue Water, White Death” - it shows valerie taylor diving with oceanic whitetips
Kommentare