Title: Use of tail in Cownose rays while swimming Author: Elizabeth Kane Abstract This study looked at the role of the tail of a Cownose ray while swimming. The swimming ability of a Cownose ray at the Shedd Aquarium without a tail was compared to the swimming ability of a Cownose ray with a tail. The study was performed by counting the number of flaps of the pectoral fins as the ray was swimming for both the ray without a tail and a ray with a tail in the same tank. The average number of fin flaps per interval for the ray with a tail was 14.5 and for the ray without a tail was 15.6. There was no significant difference in the number of fin flaps per thirty-second interval between the two rays studied. The hypothesis was not supported by this study, but the importance of the tail in swimming is hard to determine given the conditions the study was performed under and the lack of individuals observed. Loss of the tail in the wild would impair the thrust, protection, and mating opportunities of the ray. The steering abilities of the Cownose ray are potentially impaired by the loss of tail, but further studies need to be performed in order to come to a distinct conclusion. Introduction Cownose rays have an easily identifiable face and long pectoral fins, making the species readily recognizable. The large pectoral fins stereotypical to the species are used to propel the ray through the water, and the tail is used to provide thrust when swimming with speed (Rosenberger, 2001). The Cownose ray is considered more oscillatory in its pectoral fin motion, which results in more flaps of its fins
while swimming when compared to other species of rays (Rosenberger, 2001). In addition to thrust, the tail of the Cownose ray has a small spine close to the animal’s body. The spine is serrated and has a small amount venom that can be used in defense against predators (Web 2016, Florida Museum of Natural History). Along with protection the tail of rays is used in mate selection and copulation, and the loss of tails is not common. It is believed that the tail in Batoids is an important organ that rarely experiences abnormalities (Orlov, 2011). Beyond the use of the tail for thrust, little research has been done to determine if the tail of the Cownose ray plays more of a role while the animal is swimming. In this paper I test the hypothesis that a Cownose ray without a tail will have to flap its pectoral fins more than a Cownose ray with a tail because the ray without a tail will use the pectoral fins to serve the role of both organs while swimming. This was done by comparing one ray in the tank that had a tail with the one ray in the tank that did not have a tail. The tail of the ray was completely lost to a Queen triggerfish that had been living in the tank prior to the incident. The Queen triggerfish has teeth and strong jaws, but generally feeds on molluscs, crustaceans, and echinoderms rather than rays (Web 2016, ARKive). Methods A Cownose ray with a tail about the length of its body and a Cownose ray without a tail were observed in the Caribbean Reef exhibit at the Shedd Aquarium. The Caribbean Reef is located in a 90,000 gallon, regularly filtered tank and contains about 400 species of fish. Each ray was observed for ten thirty-second intervals for a total of five minutes of observation each. Each interval was determined using a
timer. During each interval the number of flaps that the ray took were counted by following the ray around the circular tank and recorded. One flap was considered a full up and down motion of the ray’s pectoral fins. The number of flaps per interval were then averaged over the total observation period. Results The Cownose ray with a tail took an average of 14.5 flaps of its pectoral fins per thirty-second interval. The Cownose ray without a tail took an average of 15.6 flaps of its pectoral wings per thirty-second interval (Figure 1). There was no significant difference between the number of flaps the ray with a tail took compared to the number of flaps the ray without a tail took (t-test; df= 17.61, t= -0.86, p= 0.4008).
Petoral fin flaps (30 sec interval)
Average pectoral fin flaps of Ray with or without a tail 15.8 15.6 15.4 15.2 15 14.8 14.6 14.4 14.2 14 13.8 Ray with tail
Ray without tail
Ray Observed
Figure 1: The average number of pectoral fin flaps for both a ray with a tail and a ray without a tail while swimming through the Caribbean reef exhibit at the Shedd Aquarium. The ray without a tail had more flaps per thirty-second interval, but the difference was not significant.
Discussion The difference in the average number of pectoral fin flaps between the ray with a tail and the ray without a tail were not significant, thus not supporting the hypothesis that a ray without a tail would need to flap its fins more often while swimming. This result would lead to the conclusion that the tail of a Cownose ray does not play a significant role in how the animal swims, and that they rely primarily on the pectoral fins. Though the hypothesis was not supported as a result of this study that does not mean that the tail of a Cownose ray does not play a role in helping the species swim. One study found that the tail helps in steering, though no further explanation was provided (Orlov, 2011). In other species of fish, the loss of the caudal fin has meant lower critical swimming speeds and a higher active metabolism (Fu et al., 2013). Though the Cownose ray does not have a caudal fin, a measure of metabolic rate and swimming speed would be an interesting further study to show the finer impacts of tail loss in this species. Limitations to this study could have contributed to the lack of significance. The experiment was conducted in extremely controlled conditions and the rays were living in a tank much smaller than the typical range this species inhabits. Had the ray without a tail needed to accelerate quickly, the lack of tail would have impaired the thrust that the ray could have achieved, an important aspect of this species in the wild during migrations (Rosenberger, 2001). Another limitation is that the study only looked at one ray with a tail and only for five minutes total. Had the study looked at more rays for a longer period of time different results would have likely been found. The Shedd Aquarium is a popular and crowded destination, with the
Caribbean reef being a charismatic exhibit. The observation methods employed here easily could have contributed to the lack of significant results due to the crowds and the circular tank making it easy to miss a fin flap. The rays were fed and a diver entered the tank during data collection, so the collection period was interrupted which is another possible explanation for the observed result. The diver entering the tank was a clear indication that it was feeding time, which is a possible explanation for the activity levels observed in the rays studied. The limitations and possibility for error are likely contributors to the final results It is difficult to conclude at this time the specific role of the tail in swimming based on the results found in this study. The rays at the Shedd Aquarium are maintained and cared for, but the lack of a tail in the wild would inhibit the ray in other ways. Complete tail loss in the wild is uncommon due to the importance in protection from predators, courtship, and copulation (Orlov, 2011). Further studies of the role of the tail while the ray is swimming are needed to determine the exact role of this organ. Other studies looking further into how the species uses the tail in other ways would be enlightening. Any studies that would be possible to perform on a wild population would be extremely informative and interesting, especially for a ray that did not have a tail. A comparative study between tail use in different species of rays would be interesting as well, and would likely provide more information on the importance of the tail and its various uses.
Average flaps per interval with a tail 14.5
Average flaps per interval without a tail 15.6
P value- twotailed t-test
Degrees of freedom
T value
0.4008
17.61
-0.86
Table 1: Summary table of the results found in this study, including the average number of flaps per minute and the statistical data found. Literature Cited Fu, C., Z.-D. Cao, and S.-J. Fu. "The Effects of Caudal Fin Loss and Regeneration on the Swimming Performance of Three Cyprinid Fish Species with Different Swimming Capacities."Journal of Experimental Biology 216.16 (2013): 3164174. Google Scholar. Web. Kittle, Kimberly. "Rhinoptera Bonasus." :: Florida Museum of Natural History. N.p., n.d. Web. 07 May 2016. <https://www.flmnh.ufl.edu/fish/discover/speciesprofiles/rhinoptera-bonasus/>. Orlov, Alexei M. "Record of a Tailless Richardson's Ray Bathyraja Richardsoni (Garrick, 1961) (Rajiformes: Arhynchobatidae) Caught off the Mid-Atlantic Ridge." Pan-American Journal of Aquatic Sciences 6.3 (2011): 232-36. Google Scholar. Web. "Queen Triggerfish Photos and Facts." ARKive. N.p., n.d. Web. 07 May 2016. <http://www.arkive.org/queen-triggerfish/balistes-vetula/>. Rosenberger, Lisa J. "Pectoral Fin Locomotion in Batoid Fishes: Undulation vs Oscillation." Journal of Experimental Biology 204 (2001): 379-94. Google Scholar. Web. 07 May 2016.