Tuesday, June 14, 2016

More Fascinating than a Ninja Lanternshark? by Hunter Ritchie

            The Ninja Lanternshark Etmopterus benchleyi is a recently discovered deep water shark species. What makes this species so different and name fitting compared to other deep water sharks, is its unique body and behavior. This shark is of the genus Etmopterus, which is one of the most species-rich and diverse genera of sharks (Eschmeyer and Fricke 2015). The shark was first described off the Pacific coast of Central America by a Spanish research vessel. The research vessel was trawling the bottom from 836-1443 m deep a lot the continental slope. This shark is named in honor of the author of Jaws who is an avid shark conservationist; its common name is derived from its uniform black coloration and stealthy behavior. Species distribution is from eastern Pacific Ocean from Nicaragua south to Panama and off Costa Rica. The maximum size the shark can grow is 515 mm. This fish has paired pectoral fins starting right behind the gill slits, paired pelvic fins starting right in front of the caudal peduncle and a very thin and narrow caudal peduncle that helps distinguish it from other sharks. This fish has a few photophores along the side of its body that allow it to slightly glow in the dark. The Ninja Lanternshark also has a big glowing eyes, lives in depths around 836-1443 meters deep, and is a uniform black color. In addition, this shark also uses ampullae of lorenzini to help detect prey.
Figure 1. Etmopterus benchleyi, n. sp., paratype, USNM 421539, immature male, 292 mm TL, fresh specimen Source
            Photophores are common in most deep water fishes. These pores  contain light filter pigments that generate light. It is hypothesized that these ventrally located photophores are used like a mirror, to mimic or reflect the blue ocean light above them, to help better camouflage them (Denton, Herring and Widder 1985). These photophores are effective in making light capable for the individual emitting it to see but while also camouflaging it by mirroring the light from above them in the water column, which it an effective technique for deep water dwelling fish.

            When living at depths of 836-1443 meters deep it is important to have some kind of ability to detect prey. One of the fascinating characteristics used to detect prey and set it apart from other deep water fish is it’s big glowing eyes relative to body size. The eye is an elliptical shape with dimensions of 4.1mm-9.1mm in length and 1.3mm-2.1mm in height. (Ebert, Long and Vasquez 2015) Having a big eye in the deep ocean water where there is hardly any light wouldn’t be a very effective hunting strategy of finding prey but since this fish emits its own light/camouflage field having a large eye enhances the fish’s vision of prey swimming nearby. The hunting strategy used by this fish are likely to be similar to other lanternsharks. Other lanternsharks spend their time roaming the benthopelagic parts of the ocean foraging for pelagic macroplankton/micronenckton, teleost fish, and cephalopods (Neiva, Coelho and Erzini 2006).

            The Ninja Lanternsharks uniform black color is unique when being compared to other deep water and lanternsharks. Color in other deep water fish ranges from a red tint to a pale gray. The behavior of this shark also aided into the naming process. The Ninja shark slowly sneaks about and has an elusive behavior that helped give it its ninja name.
Ninja Lanternshark Etmopterus benchleyi
n. sp., holotype, USNM 423195, adult female, 458 mm TL, fresh specimen.  Source
             Another fascinating adaptation to help this shark detect prey is its ampullae of lorenzini. These are sensory nerves on the head of the shark that allow it to detect movements made by other fish nearby. When combined with its photophores adding in visible light for the Lanternshark and its big eye to also aid in finding prey it makes this shark an efficient predator for deep water hunting. Other fish, such as catfish, have ampullae of lorenzini but they don’t have the stealthy combination of camouflage and hunting techniques that this shark does. 

            This species is a unique deep water shark that fits its name. Living a life devoted to stealth and hunting this shark is more resembling of a ninja than any other. Having a pitch black colored body and photophore cell that act as a mirror to the light above them this shark is virtually invisible. However, being invisible isn’t enough to be classified as a ninja, this shark also has an extremely sensitive enlarged eye and ampullae of lorenzini to help detect movement of prey and make it a very effective predator of the deep that makes it stand out from all the rest.

References

Eschmeyer, W.N. &  Fricke, R. (Eds.) (2015) Catalog of Fishes  Electronic version accessed April. 2, 2016.
Vasquez, V.E., Ebert, D.A., and Long, D.J.  (2015) Etmopterus benchleyi n. sp., a new lanternshark  (Squaliformes:Etmopteridae) from the central eastern Pacific Ocean. Journal of the Ocean Science Foundation 17   Electronic version accessed April. 2, 2016
Denton, H., Widder, C. (1985) The Roles of Filters in the Photophores of  Oceanic Animals and their Relation to Vision in the Oceanic Environment. Proceedings of the Royal Society B Biological Sciences. 
Neiva, J., Coelho, R., and Erzini, K. (2006) Feeding habits of the velvet belly lanternshark
            Etmopterus spinax (Chondrichthyes: Etmopteridae) off the Algarve, southern  Portugal. Journal of the Marine Biological Association, UK.  86:835-841  
Wueringer, B., Peverell, S.C.,  Seymour, J., Squire, L. Jr.,  Kajiura, S. M., and Collin, S.P.  (2011) Sensory systems in sawfish. 1. The ampullae of Lorenzini.   Brain Behavior and Evolution 78(2):139-49


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