Featured Species: Longfin Mako (Isurus paucus)

This week’s featured species is a highly skilled oceanic predator who was recently reclassified as an Endangered Species. The Longfin Mako (Isurus paucus) is a member of the family Lamnidae and the closest cousin to the shortfin mako (Isurus oxyrinchus). They have long gills, large eyes, and wicked looking teeth that protrude from their lower jaw. They are aptly named the longfin mako because of their long pectoral fins, which can be as long as their head with relatively broad tips (Ebert, Fowler, & Dando, 2015). The longfin mako is the closest relative of the shortfin mako, however, there are several distinct differences between the two species. The shortfin mako has a sharply pointed snout and relatively short pectoral fins; while the longfin mako has a rounder snout with incredibly long pectoral fins. The longfin mako also has a ridge running from the back of the head over the gills to the pectoral fins (Ebert, Fowler, Dando, 2015). Unlike the shortfin mako, whose biology and life history characteristics have been well studied, the longfin mako is still relatively unknown. The both the shortfin and longfin makos are Endangered species, as categorized by the International Union for the Conservation of Nature (IUCN).

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Clemens, D. (Author). (2015). Longfin Mako [Digital Image]. Retrieved from http://www.discovery.com/

The longfin mako is a fast, epi- to mesopelagic predator. They feed primarily on fast oceanic prey items like tuna. As such, their teeth are highly adapted for catching and grasping slippery prey items. They have a wide triangular base with narrow cusps. The teeth in the upper and lower jaws have both smooth and cutting edges (Rigby et al, 2019). When compared to their cousin the shortfin mako, the third tooth of the longfin mako is more symmetrical and has straighter edges.

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Left: Robertson, D.R. (Photographer). (2016). Isurus paucus lower teeth [Digital Image]. Retrieved from https://commons.wikimedia.org/ Center: Robertson, D.R. (Photographer). (2016). Isurus paucus jaws [Digital Image]. Retrieved from https://commons.wikimedia.org/ Right: Robertson, D.R. (Photographer). (2016). Isurus paucus upper teeth [Digital Image]. Retrieved from https://commons.wikimedia.org/

The family Lamnidae contain five species in three genera.

What makes family Lamnidae different from most other sharks is that they are warm-blooded. Unlike other species of sharks which are cold blooded and rely on the surrounding water temperature to thermoregulate their bodies, the sharks in the family Lamnidae, as well as family Alopiidae which contains the thresher sharks, are warm-blooded – sort of. These endothermic sharks have a modified circulatory system that allows them to elevate the temperatures of certain organs (such as the eyes, brain, heart, stomach, and trunk muscles) through a process called counter-current heat exchange.  Cool, oxygen depleted blood travels through the thin-walled veins from the red muscles, where it is warmed again by the oxygen rich blood from the gills through thick-walled arteries  (Klimley, 2013). This internal network of veins and arteries is known as the rete mirable, or “wonderful net” in Latin (Klimley, 2013).

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Counter-current heat exchange (n.d.). [Digital Image]. Retrieved from http://bio1152.nicerweb.com/

 

The longfin mako is caught globally in targeted and bycatch fisheries. The majority of landings are due to bycatch of industrial pelagic fleets including coastal longlines, gillnets, trammel nets, and the occasional trawls (Camhi, Pikitch, & Babcock, 2008; Martínez-Ortiz, Aires-da-Silva, Lennert-Cody, & Maunder, 2015).  When they are caught, they are retained for their meat and their fins are sold in the Asian fin market (Clarke, Magnussen, Abercrombie, McAllister, & Shivji, 2006). The longfin mako is reported less frequently in Hong Kong markets than the shortfin mako, however, their presence has been documented. At present, there is no global population size or structure data available for the longfin mako (Rigby et al., 2019). The only available data comes from the standardized catch-per-unit-effort (CPUE) from the Atlantic Ocean United States Pelgaic Longline Fishery (Rigby et al., 2019). Data from CPUE is considered to be more reliable than fishery logbook data (Lynch, Shertzer, Cortes, & Latour, 2018). The catch rate for the longfin mako over a 24 year period (1992-2015) has shown declines in populations in the mid 1990’s, followed by a short period of population increase in the early 2000’s before a continued decline. The data indicates an annual decline rate of 3.7%, which, if continued over the next three generations (75 years), will result in a population decline of 93.4% (Winker, Carvalho, & Kapur, 2018).

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NOAA Observer Program (Photographer). (2009). Isurus paucus [Digital Image]. Retrieved from https://commons.wikimedia.org/wiki/File:Isurus_paucus_2.jpg

In an effort to conserve the longfin mako, they were added to Appendix II of the Convention on Migratory Species (CMS) in 2008. The CMS memorandum aims at facilitating conservation of migratory shark species. Last year in 2018, Mexico announced their intention to add the longfin mako to Appendix II of the Convention on International Trade in Endangered Species (CITES). If adapted this year, it will restrict longfin mako exports. Any trade would need to be accompanied by permits, which would be granted on the basis that the mako was caught as a product of legal and sustainable fisheries (Rigby et al., 2019). Earlier this year, the IUCN re-evaluated the longfin mako’s classification to Endangered. If conservation of this species is to be successful, improved reporting on catch and discard data of the longfin mako is needed, as well as full implementation and enforcement of agreed upon international treaties (Rigby et al., 2019).

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BlueBoat Ken (Videographer). (2011). Longfin Mako [Video Clip]. Retrieved from https://www.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: Gvitart, 1966

Family: Lamnidae, 5 species

Length: Up to 14 feet (4.3 m)

Weight: Up to 160 lbs (72.5 kg)

Habitat: Poorly known; Most likely epipelagic in deep water

Depth: Surface up to 5750 feet (1752 m)

Reproduction: Ovoviviparity with oophagy

Gestation: Suspected 15 -18 months

Litter Range: 2 – 8 pups

Home Range: Likely occur in all oceans worldwide, though distribution is poorly recorded

Diet: Pelagic bony fishes

IUCN Status: Endangered

(Ebert, Fowler, & Dando, 2015; Rigby et al., 2019)

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 wonderful Longfin Mako! If you missed last week’s featured species, please be sure to check out the amazing Sixgill Sawshark! 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

Ocean Treasures (Author). (n.d.). Longfin Mako [Digital Image]. Retrieved from https://otlibrary.com/long-finned-mako-shark/

Literature Cited

Camhi, M. D., Pikitch, E. K., & Babcock, E. A. (2008). Introduction to sharks of the open ocean. Sharks of the open ocean: biology, fisheries and conservation. Blackwell Scientific Publications, Oxford, UK, 1-13.

Clarke, S. C., Magnussen, J. E., Abercrombie, D. L., McAllister, M. K., & Shivji, M. S. (2006). Identification of shark species composition and proportion in the Hong Kong shark fin market based on molecular genetics and trade records. Conservation Biology20(1), 201-211.

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

Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.

Lynch, P. D., Shertzer, K. W., Cortés, E., Latour, R. J., & Handling editor: Manuel Hidalgo. (2018). Abundance trends of highly migratory species in the Atlantic Ocean: accounting for water temperature profiles. ICES Journal of Marine Science75(4), 1427-1438.

Martínez-Ortiz, J., Aires-da-Silva, A. M., Lennert-Cody, C. E., & Maunder, M. N. (2015). The Ecuadorian artisanal fishery for large pelagics: species composition and spatio-temporal dynamics. PloS one10(8), e0135136.

Rigby, C.L., Barreto, R., Carlson, J., Fernando, D., Fordham, S., Francis, M.P., Jabado, R.W., Liu, K.M., Marshall, A., Pacoureau, N., Romanov, E., Sherley, R.B. & Winker, H. (2019). Isurus paucusThe IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/60225/3095898

Winker, H., Carvalho, F., & Kapur, M. (2018). JABBA: Just Another Bayesian Biomass Assessment. Fisheries Research204, 275-288.

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