This Friday’s Featured Species profile is going to the flat sharks: the stingrays! The Cownose Ray (Rhinoptera bonasus) is one of my favorite species. They have a distinct cow shaped nose that is just so adorable I always want to boop them on the nose! -Ok not really, I’d never actually do that! But still, they are adorable!
Like other stingrays and skates, the cownose ray uses their modified pectoral fins to propel themselves forward. Skates and rays have two different methods of locomotion. Some, like the southern stingray (Dasyatis americana) use undulatory propulsion, which is characterized by a wave-like motion transferred along the pectoral fins. Others, like the cownose rays use oscillatory propulsion. These rays and skates propel themselves forwards, upwards, and downwards by flapping – or oscillating – their pectoral fins up and down. Chimeras use a similar method of locomotion (Klimley, 2013). Below, you can see the three primary swimming methods of sharks (a- anguilliform, b- carangiform, and c- thunniform), as well as the undulatory (d) and oscillatory (e) motions of skates and rays, and finally the oscillatory (f) method of chimeras.
Cownose rays are pelagic swimmers but they are benthic feeders, meaning they search the sea floor for their prey. They swim close to the sea floor, sweeping back and forth, using their chemo- and electroreceptors to locate their prey (Klimley, 2013). These rays generally feed on scallops, soft-shell and hard-shell clams, and oysters (Klimley, 2013; Grubbs, et al., 2016). To break through their prey’s hard exterior, cownose rays have developed a series of flattened tooth plates, similar to nut cracker, that crushes through their prey (Tricas, et al., 1997).
In the last 3 decades, pressure from fisheries have led to a global decrease in large shark populations (Clarke, Harley, Hoyle, & Rice, 2013; Dulvy et al., 2008). As these populations have decreased, smaller mesopredators, like the cownose ray, have seen increases in population size due to a reduction in predation from larger sharks (Grubbs, et al., 2016; Klimley, 2013). Along the coast of the eastern United States, cownose ray populations have increased 10 fold since the 1970’s (Klimley, 2013). As these populations have increased, commercial scallop fisheries have seen a dramatic decline in the bay scallop (Argopecten irradians) populations. This inverse relationship of predator and prey populations suggests an increase in scallop predation by the cownose ray. The removal of a large predator from the food chain leads to cascading impacts on the abundance of species lower in the food chain (Grubbs, et al., 2016). This is called a trophic cascade.
At present time, the cownose ray is listed as Near Threatened due to heavy and often unregulated fisheries in Central and South America (Baker, 2006). In the United States, there is no fisheries industry for the cownose ray, however, they are sometimes taken as bycatch by commercial fisheries employing pound nets, shrimp trawls, and haul selines (Klimley, 2013). This population is currently considered Least Concern. However, due to their schooling behavior and low fecundity, if a fisheries industry were to be established, cownose rays could be at risk of over exploitation without strict regulation (Baker, 2006). At this time, there are no conservation legislation that protects the cownose ray.
AnimalsWorldTV. (Videographer). (2015 August 24). Migration Stingray [Video Clip]. Retrieved from https://www.youtube.com/
Authority: Mitchill, 1815
Family: Rhinopteridae, 8 species
Size: Disc Width Up To 3.5 feet (1.07 m)
Weight: Maximum weight unknown
Habitat: Shallow Marine and Brackish Waters
Depth: Shallow waters 0 – 72 feet (0 – 22 m)
Reproduction: Aplacental Viviparous
Gestation: Unclear reproductive cycle. Up to 11 -12 months; as little as 5 -6 months
Litter Range: 1 pup per cycle; though 6 embryos have been reported
Home Range: Continental shelves in temperate and tropical waters of the Western Atlantic Ocean.
IUCN Status: Near Threatened Globally due to unregulated inshore fisheries in Central and South America; Least Concern in North America
(Smith, 1986; Tricas, et al., 1997; Neer, & Thompson, 2005; Baker, 2006)
Thank you for checking out this week’s featured species. Don’t miss a Feature! Check out last week’s biofluorescent species: the Chain Catshark.
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. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!
As always, remember you can make a difference for marine ecosystems by contacting your Congress man or woman and telling them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics!
Featured Image Source
Flannery, A. (Photographer). (2018 June 12). Cownose ray [Digital Image].
Barker, A.S. 2006. Rhinoptera bonasus. The IUCN Red List of Threatened Species 2006: e.T60128A12310195.
Clarke, S. C., Harley, S. J., Hoyle, S. D., & Rice, J. S. (2013). Population Trends in Pacific Oceanic Sharks and the Utility of Regulations on Shark Finning. Conservation Biology, 27(1).
Dulvy, N. K., Baum, J. K., Clarke, S., Compagno, L. J. V, Cortés, E., Domingo, A., … Valenti, S. (2008). You can swim but you can’t hide: The global status and conservation of oceanic pelagic sharks and rays. Aquatic Conservation: Marine
Grubbs, R. D., Carlson, J. K., Romine, J. G., Curtis, T. H., McElroy, W. D., McCandless, C. T., … Musick, J. A. (2016). Critical assessment and ramifications of a purported marine trophic cascade. Scientific Reports, 6, 20970.
Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.
Neer, J. A., & Thompson, B. A. (2005). Life history of the cownose ray, Rhinoptera bonasus, in the northern Gulf of Mexico, with comments on geographic variability in life history traits. Environmental Biology of Fishes, 73(3), 321-331.
Smith, M. S. (1986). Observations on the reproductive biology of the cownose ray, Rhinoptera bonasus, in Chesapeake Bay. Fish. Bull., 4, 871-877.
Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.