Physiology and Adaptations of the Goblin Shark - Research Paper Example

? Physiology and Adaptations of the Goblin Shark Physiology and Adaptations of the Goblin Shark Sharks are cartilaginous fishes belonging to the Chondrichthyes, which also include rays and chimeras (Compagno, 1990). They are members of one of the oldest and most successful group of jawed fishes with around 1000 living known species. The success of the sharks can be attributed to the diversity of their evolution, having a simple yet flexible skeleton, as well as being hardy creatures, even withstanding the wide-ranged extinctions of numerous species during the Permian-Triassic transition (Compagno, 1990). Sharks are mostly found in tropical to warm-temperate waters, and can live in depths as deep as 2000 meters. The most common shape that is associated with sharks is the fusiform shape, such as the one seen in the Great White Shark. However, in reality sharks have various shapes and sizes to suit their prey and environment. The most well-known example of these is the hammerhead shark, from the family Sphyrnidae, which have a flattened structure on their heads that also houses the eyes, making it look like a hammer (Compagno, 1990). There are also other well-known sharks that seem to resemble rays due to their flat bodies, or those that resemble whales with regards to their body and mouth shapes. In this paper, a poorly-known but also one of the most unusual-looking species of sharks, the goblin shark would be discussed as to how its adaptations have lead to its unique body shape, skin color, and jaws. Goblin Shark Descriptions and Physiological Adaptations The goblin shark, (Mitsukurina owstoni Jordan, 1898) is a deep-dwelling shark that is established as one of the sole extant species of its family, Mitsukurinidae, order Lamniformes, with the rest to be only known from collected fossils (Parsons, Ingram, & Harvard, 2002). It is a poorly- known, elusive deepwater fish, with only around 33 established literatures about its studies, 22 of those are from the vicinity of the Izu Islands, and the rest are scattered across the globe (Duffy, 1997). Thus, until now it is a species that is not well-understood, including its other feeding habits, growth and development patterns, as well as its reproductive cycle. What also makes it harder to study is that once caught off-shore and brought to aquariums, it dies within a span of a week (Compagno, 2000 as cited in Grijalba-Bendeck & Acevedo, 2009; Yano, Miya, Aizawa, & Noichi, 2007). The holotype of the species was captured in 1898 somewhere in the Bay of Tokyo, and most of the other early specimens that were subsequently caught were also found near that part of Japan (Jordan, 1898 as cited in Bean, 1905; Dean, 1903; Duffy, 1997; Hussakof, 1909; Parsons, Ingram, & Harvard, 2002). The shark seems to be a well-known species along the coasts of Izu, where the locals call it Tengu-zame, translated as elfin or goblin shark (Bean, 1905). Its large liver is used as an oil source, and the flesh is used as fertilizer. While being seen as rare in most parts of the world, the species seems to be a common bycatch in long line and bottom trawling nets, which suggests that it prefers to live near the meso-pelagic to near-benthic zones (Duffy, 1997; Grijalba-Bendeck & Acevedo, 2009). Other areas where the species are also seen and collected are in Australia, the Indian Ocean, South Africa, French Guiana, Europe, the Gulf of Mexico, and New Zealand (Duffy, 1997; Parsons, Ingram, & Harvard, 2002). The goblin shark has a flat, elongated blade-like snout called the rostrum, small eyes, flabby body, slender teeth and a caudal fin that has no ventral lobe and resembles that of the thresher shark (Yano, Miya, Aizawa, & Noichi, 2007). This rostral appendage is shorter in adult sharks as compared to younger ones (Bean, 1905; Duffy, 1997; Grijalba-Bendeck & Acevedo, 2009). The shark has rounded fins and a body color that ranges from light reddish-brown to pink, with the fins having colors a few tones darker (Bean, 1905; Duffy, 1997; Grijalba-Bendeck & Acevedo, 2009). The most noticeable part of the goblin shark is its head, which is flexible to accommodate fast-moving prey and keep them in effectively (Duffy, 1997). The goblin shark is able to retract its protrusible jaws, which when accompanied by the rapid projection of the head, depression of the tongue and expansion of the buccal cavity, allows the goblin shark to suck in its prey (Duffy, 1997; Wetherbee & Kajiura, 2000). The teeth are low and blade-like, long and slender, positioned forward with three rows, and are much more numerous and longer at the extremity of the jaw compared to the posterior part (Bean, 1905; Duffy, 1997; Grijalba-Bendeck & Acevedo, 2009). When the jaw is not protruding, the goblin shark resembles the grey nurse shark, with a long, slender snout (Duffy, 1997). An old photograph of a mounted specimen and a newer photograph of a young goblin shark are shown in figures 1 and 2, respectively. The shark’s diet is mostly composed of squids, ostracods, copepods, isopods, decapods and teleost fishes, which are also the same food consumed by other meso-pelagic to bentho-pelagic species (Duffy, 1997; Yano, Miya, Aizawa, & Noichi, 2007). There are times however, that some sharks are caught with empty stomachs, and occasionally some are found to have human refuse in them, suggesting that goblin sharks might also dwell on shallower waters from time to time (Duffy, 1997; Yano, Miya, Aizawa, & Noichi, 2007). As with other sharks, goblin sharks are able to detect prey by means of using electro-receptive organs called ampullae of Lorenzini, which detect weak electric charges outside its body. Among members of the elasmobranch group of fishes, which include most cartilaginous fish, these ampullae are connected to the pores on the surface of the skin, surrounded by a single Figure 1. A photograph of a mounted goblin shark, taken by Barton Bean around 1905 Figure 2. A photograph of a young goblin shark taken by Jose Castro in Chiba Prefecture, Japan in 2007 (Etnoyer, P. 2007. Poster child for earth day? Retrieved on November 7, 2012 from http://scienceblogs.com/deepseanews/2007/04/21/poster-child-for-earth-day/) layer of sensory epithelium filled with a conductive low-resistance mucopolysaccharide, thus creating a skin that detects electrical signals (Sisneros & Tricas, 2002). The positions of the canals where the ampullae are situated could permit the detection of electrical fields by small prey or by other inanimate objects that also emit weak electrical signals. The ampulla chambers contain receptor cells that measure the transcutaneous potential drop, which is dependent of the distance of the ampulla chamber and the pores of the skin. When the ampullae chambers have a long, spatial separation with the pores, the skin is able to detect electrical signals within a larger field (Sisneros & Tricas, 2002). Having this kind of system allows the goblin shark to detect its prey as it glides along the bottom of the ocean floor, even in the dark. The flaccid body of the shark is comparable to other deep-dwelling species like the chimaera, which are not active swimmers (Dean, 1903; Duffy, 1997). This adaptation can be attributed to the goblin shark evolving to match the specific gravity of seawater (Duffy, 1997). Also, because of higher water pressures exerted on the shark as it swims as the deepest depths, its body needs additional flexibility to counteract the pressure and prevent itself from being crushed. The streamlined body allows it to move smoothly, much like its pelagic cousins. This also helps the sharks to swim normally whenever they swim up to the surface (Duffy, 1997). The shark has relatively small eyes compared to other shark species, mainly because it does not need it for seeing, as it mostly dwells in the deepest parts of the ocean where sunlight cannot reach. Also, as a bottom-dwelling animal without much use for sight, it lacks a nictitating membrane, which is often seen in other pelagic shark species Grijalba-Bendeck & Acevedo, 2009). Goblin sharks only has a small, white spot called a pineal window which they use to detect light, and this is most often found in other deep-water dwelling sharks (Duffy, 1997). Aside from all other information available, there are not much data about other habits of the shark, which can be attributed to it being seemingly pressure-sensitive, and that it has a very short lifespan when taken out of the water and placed in aquariums or fish tanks (Compagno, 2000 as cited in Grijalba-Bendeck & Acevedo, 2009; Yano, Miya, Aizawa, & Noichi, 2007). Conclusion Goblin sharks, Mitsukurina owstoni Jordan, are the sole living members of the family Mistukurinidae, which includes other discovered fossil remnants with similar characteristics. It is known to be a deep-dwelling shark, which at times swim up towards shallow waters for a short time. They are most often seen when caught along other fish as bycatch in long lines or nets that extend to the bottom or deep oceans. The goblin shark has a fusiform body shape, which is typical among other shark species. It also has a limp body, which is capable of enduring enormous water pressures at the lowest depths of the ocean. The coloring of the shark ranges from light brown to pink, which is also a characteristic of other bottom or deep-sea dwelling organisms. It has very small eyes due to its adaptation of living in a very dark place where there is no need for eyesight. While the eyes have reduced function, the goblin shark’s skin has highly adapted for hunting in the dark through the use of its electro-responsive organs, called the ampullae of Lorenzini. The shark also has a unique, protruding jaw that can project itself to catch prey, as well as a long rostrum which resembles a thin, long blade. Due to their elusive nature and tendencies to die when being kept alive, not much is studied about goblin sharks except for a few data published. Thus most studies regarding this fish are very limited. Nevertheless, efforts made by scientists were able to explain the ways in which the goblin shark has evolved and survived as a living fossil in today’s oceans. References Bean, B. (1905). Notes of an adult goblin shark (mitsukurina owstoni) of Japan. Proceedings U.S. National Museum, 28:815-818. Compagno, L. (1990). Alternative life-history styles of cartilaginous fishes in time and space. Environmental Biology of Fishes, 28:33-75. Dean, B. (1903). Additional specimens of the Japanese shark, mitsukurina. Science, 17(433): 630-631. Duffy, C. (1997). Further records of the goblin shark, mitsukurina owstoni (lamniformes: mitsukurinidae), from New Zealand. New Zealand Journal of Zoology, 24:167-171. Grijalba-Bendeck, M., & Acevedo, K. (2009). Mitsukurina owstoni jordan (chondrichthyes: mitsukurinidae) first record for the colombian caribbean. Bol. Invemar, 38(1): 211-215. Hussakof, L. (1909). A new goblin shark, Scapanorhynchus Jordani, from Japan. Bulletin American Museum of Natural History, 26: 257-261. Parsons, G., Ingram, G. J., & Harvard, R. (2002). First record of the goblin shark mitsukurina owstoni jordan (family mitsukurinidae) in the gulf of Mexico. Southeastern Naturalist, 1(2): 189-192. Sisneros, J., & Tricas, T. (2002). Neuroethology and life history adaptations of the elasmobranch electric sense. Journal of Physiology - Paris, 96: 379-389. Wetherbee, B., & Kajiura, S. (2000). Occurrence of a rare squaloid shark, Trigonognathus kabeyai, from the Hawaiian islands. Pacific Science, 54(4): 389-394. Yano, K., Miya, M., Aizawa, M., & Noichi, T. (2007). Some aspects of the biology of the goblin shark, mitsukurina owstoni, collected from the Tokyo submarine canyon and adjacent waters, Japan. Ichthyological Research, 54: 388-398. List of Figures Figure Title Page 1 A photograph of a mounted goblin shark, taken by Barton Bean around 1905 5 2 A photograph of a young goblin shark taken by Jose Castro in Chiba Prefecture, Japan in 2007 5 Read More