Dananananananana BAT RAY

Guest Blogger: Angela Schmidt

The following guest post was voted best in the class for an undergraduate assignment on fish adaptation from Humboldt State University’s Fall 2016 Fish Conservation and Management course taught by Dr. Andre Buchheister. The assignment required students to find a peer-reviewed article on a fascinating fish adaptation or species and to communicate the scientific information in a blog format to a general audience. 

Alias Bat Ray
Secret Identity Myliobatis californica
Classification Class – Chondrichthyes, Superorder Batoidea, Order Myliobatiformes
Range Pacific Ocean from Oregon to the Gulf of California; can inhabit estuarine areas
Max. Size 6ft in width;  > 200 lbs.
Max. Age ~35 years
Sexual Maturation Males – 2-4 years; Females – 5-7 years
Reproductive Strategy Eggs are internally fertilized and offspring are born live (ovoviviparous) and individuals can reproduce more than once throughout their lives (iteroparous); gestation (pregnancy) lasts 9-12 months
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A ventral view of a Bat Ray up in the water column. Though these organisms are largely benthic, they are capable of pelagic swimming. The obvious countershading shown aids the Bat Ray in the evasion of predators.

Like Gotham’s caped crusader, Bat Rays soar through their surroundings. However, where Bruce Wayne maneuvers through the air between buildings, Bat Rays use their wing-like pectoral fins to “fly” along the ocean floor.  This behavior classifies Bat Rays, as well as other bottom-dwelling animals, as “benthic” (Gray 1997). This classification is also supported by the Bat Ray’s specific body shape. They are broad and flat, which allows them to glide along the ocean floor.

Another similarity that Bat Rays share with Batman is their fondness of dark colors. Where Bruce dons his pitch-black cape, Bat Rays exhibit a dark brown to black coloration. This camouflage helps the Bat Rays to avoid predation from above (Gates 1997).

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A jaw of a Bat Ray. The Bat Ray has a unique type of dentition called “pavement” referring to the broad flat plates that make up the ray’s teeth. (neotropicalfishes.myspecies.info/)

Because Bat Rays are benthic, they feed primarily on benthic crustaceans and mollusks, including bivalves (Gray 1997). Though the thick, tough shells of these animals would pose a problem for many other predators, Bat Rays are equipped with a unique type of teeth called pavement dentition (Follet 1957). The term “pavement” refers to the broad flattened plates in a Bat Ray’s mouth that it uses to crush the hard exteriors that protect most of its prey.

Unfortunately, not all of Batman’s and the Bat Ray’s similarities are so beneficial. Like the Dark Knight, the Bat Ray is often misunderstood in the public’s eye. The Bat Ray is an elasmobranch, a classification of cartilaginous carnivores that include sharks, skates and rays. The Bat Ray’s close relation to sharks makes people wary as to whether these rays are friends or foes.

Additionally, the Bat Ray possesses a dangerous defense mechanism, a barbed stinger located near the base of its whip-like tail (Gray 1997). When threatened, the Bat Ray uses its venomous stinger to ward off predators. However, as the Bat Ray is benthic, it is often stepped on by unwitting beachgoers. This can lead the ray to sting the person in an attempt to protect itself. Thus the person, not knowing any better, is left with a painful injury and a bitter memory of the Bat Ray.

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The Bat Ray’s barbed stinger. The stinger is located near the base of the tail and is poisonous. (pierfishing.com)

The dispute between Bat Rays and humans extends beyond the stray beach sting. In the mid to late 1900s, oyster culturists in Humboldt Bay killed more than 54,000 Bat Rays over the course of 37 years (Gray 1997). Oyster farmers believed the rays were feeding on their oysters because they saw evidence of body imprints near the oyster beds. These imprints, comparable to Batman’s Bat-signal, are made when the Bat Ray feeds as well as when they attempt to hide from predators (Hoeing 1990).  There is little scientific evidence to support the claims that the Bat Ray was feeding on oysters; just another unfortunate misunderstanding.

Super-sensing

Its teeth are not the only special adaptation that the Bat Ray possesses. In fact, the Bat Ray has a type of a sixth sense that allows it to detect weak electrical fields (Jordan 2009). This ability is made possible by an electrosensory system. The electrosensory system of a Bat Ray is made up of a number of electro-sensitive pores in the surface of the skin that are connected to ampullae by channels of a highly-conductive, gel-like substance (Jordan 2008). The Bat Ray uses its electrosensory systems to locate prey items. When an animal, such as a crustacean, moves, its muscles produce an electrical field. This field can then be picked up by a Bat Ray’s electrosensory system and signals that a potential meal is nearby (Jordan 2009). The Bat Ray is then able to follow the electrical impulse and locate the prey. Additionally, because the Bat Ray’s mouth is not within view of its eyes, the electrosensory system assists the Bat Ray in successfully detecting and manipulating its prey without requiring the use of vision.

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A diagram comparing the distribution of electrosensory organs, depicted by the red dots, in a Bat Ray (bottom) and a Pelagic Stingray (top). (Jordan 2008)

Interestingly, not all species of sharks and rays have the same number or patterns of distribution of electro-sensitive pores on their bodies (Kempster 2012). For example, the Bat Ray was found to have almost triple the number of ventral pores that the Pelagic Stingray (Pteroplatytrygon violacea) has (see above). Additionally, the Pelagic Stingray has pores spread along the middle of its ventral surface while the pores on the Bat Ray were primarily located on and around the rostrum, or head region, specifically the mouth (Jordan 2008).  This discrepancy can be explained by the different niches utilized by each species. While the Bat Ray is a largely benthic species, the Pelagic Ray, as its name implies, spends most of its time in the water column.

Not All Heroes

As Bruce Wayne watches over Gotham from the shadows, Bat Rays flex their evolutionary muscle behind a veil of misunderstanding. Until the Bat Ray is better understood, it will continue to be used as a scapegoat for oyster culturists and be seen as a danger to the general public. Just as other sources of fear, the alarm around Bat Rays stems largely from a lack of information. It important for the public to seek knowledge about this amazing creature before they deem it a villain. The Bat Ray is a key benthic predator and a model example of unique sensory adaptations, two facts that make the Bat Ray a hero in its own right.

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An adult Bat Ray swimming along the bottom of a tank at the Aquarium of the Pacific. Pictured in the background is a Shovelnose Guitarfish, another species of Elasmobranch. (aquariumofpacific.org)

About the Author

authorHi all! My name is Angela Schmidt and I’m currently a senior at Humboldt State University. I am majoring in Zoology and have a minor in Fisheries Biology with a marine emphasis. I plan on graduating in May of 2017 and am looking forward to a few internship opportunities this Summer, in addition to furthering my education with a graduate degree in the coming years. Growing up, my father made a habit of taking me to the Long Beach Aquarium in an effort to ingrain in me the same passion for sea life that he had. Spoiler alert, it worked! I grew up loving the water and all types of animal life and when the time came, I decided to dedicate my life to studying animals. This line of studying has instilled in me a respect for the natural world and a strong work ethic. My major has not always been the easiest, in fact it requires a lot of patience and a constant flow of hard work, but I find that it always feeds my insatiable curiosity and leaves me feeling both accomplished and fulfilled. I am looking forward to making my mark in the world of the biological sciences and I hope that my Bat Ray article has inspired you to do the same. Hope you enjoyed it!

References

Boschung, H. 2014. Myliobatiformes. Access Science 10:1036-1097.

Follet, W. I. 1957. Fish remains from a shellmound in Marin County, California. American Antiquity 23:68-71.

Gates, D. E., H. W., Frey. 1974. Designated common names of certain marine organisms of California. State of California Department of Fish and Game Fish Bulletin, 161.

Gray, A. E., T. J., Mulligan, R. W., Hannah. 1997. Food habits, occurrence, and population structure of the Bat Rays, Myliobatis californica, in Humboldt Bay, California. Environmental Biology of Fishes 49:227-238.

Hoenig, J. M., S. H., Gruber. 1990. Life-history patterns in elasmobranchs: implications for fisheries management. NOAA Technical Report NMFS 90: 16.

Jordan, L.K.. 2008. Comparative morphology of stingray lateral line canal and electrosensory systems. Journal of Morphology 269:1325-1339.

Jordan, L. K., S. M., Kaijura, M. S., Gordon. 2009. Functional consequences of structural differences in stingray sensory systems. Part II: electrosensory system. Journal of Experimental Biology 212:3044-3050.

Kempster, R. M., I. D., McCarthy, S. P. Collin. 2012. Phylogenetic and ecological factors influencing the number and distribution of electroreceptors in elasmobranchs. Journal of Fish Biology 80:2055-2088.

Maisey, J. G. 1984. Chondrichthyan phylogeny: a look at the evidence. Journal of Vertebrate Paleontology 4:359-371.

Martin, L. K., G. M., Cailliet. 1998. Aspects of the reproduction of the Bat Ray, Myliobatis californica, in central California. Copeia 3:754-762.

 

 

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