Bonnethead Shark


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Bonnethead Shark

  1. 1. John G. Shedd Aquarium The Bonnethead Shark in Captivity Researcher: Nicholas Brandt
  2. 2. Abstract This research was undertaken in hope of gaining a better understanding of the species Sphyrna Tiburo, or commonly known as the bonnethead shark. All observations were made at the John G. Shedd Aquarium in Chicago, Illinois between the dates of March 10, 2010 and April 19, 2010. This is an ethogram case study of three bonnethead sharks on exhibition at the aquarium. These species of shark are part of the family Sphyrnidae, most renowned for their abnormal shaped “hammerheads”. The main goal of this research was to recognize any form of social behavior in this species while their being confined in captivity. They are known in the wild as highly social animals and it was my objective to detect their behaviors and record them as I witnessed them first hand at the reef exhibit. Research Description My research plan involves a detailed study of shark species Sphyrna Tiburo, or commonly referred to as the bonnethead shark, and their particular behavior in captivity. I have observed the animal at the Shedd Aquarium of Chicago where there are currently three bonnetheads swimming in a simulated yet diverse reef exhibit. The research that have undergone has been an observational study, known in the scientific community as an ethogram; the study of an animal’s behavior. It is my hope that I have gained knowledge and insight in regards not only to behavior of this particular species of shark but also to monitor the social interactions within the Caribbean Reef Exhibit at the Shedd Aquarium, which is part of an ethogram. In the relevant literature I have read it seems as though prior researchers have observed these sharks as highly social creatures, often swimming in groups as they patrol their surroundings. To the knowledge of these ethologists as well as myself, these species behave in this social manner both in the wild and in captivity. In my early observations at the aquarium, I have seen the opposite. I have watched these animals swim the tank alone, without forming
  3. 3. packs. Quite rarely do I view a shark following another, and when I do it is the small male following a larger female. What this tells me is that conditions within the reef exhibit are somehow hindering the animal’s natural behavior to form groups. It is an assumption by many that captivity behavior is naturally going to produce abnormal behavior, but nonetheless the behavior of the bonnetheads at the Shedd Aquarium still raises questions regarding whether or not the animal is exhibiting typical captive behavior or abnormal captive behavior. The methods of gathering data are similar to those of a prior study done by Arthur A. Myberg and Samuel H. Gruber in which the two scientists identified typical behaviors of the bonnethead sharks, and most of the behaviors identified are conducted by the bonnetheads of the Shedd Aquarium. Such behaviors include Following, Patrolling, Maneuvering, Jaw Snaps and Shakes, Leading, and Giving Way. These are just a few behaviors that have been previously defined, and I myself have observed Shedd-specific behaviors from the bonnethead. In order to quantify these behaviors, I have observed each shark individually, at different periods throughout the day to achieve a full range of observational data. Using a stop watch I followed a shark throughout its patrol, noting behaviors while timing the intervals, as well as taking note of how long it took the shark to complete the course of the tank. Completing the course of the tank involves defining a starting and end point, and timing the animal to see not only how long it takes but what distractions or behaviors influence that timing. Different settings within the tank such as before feeding, after feeding, with diver in the water, and without diver in the water seem to play a significant role in the shark’s behavior, in which I noted as I collected my data. I hope to find evidence that helps to draw a conclusion on the matter of the small dimensions of the tank having anything to do with the shark’s behavior suggesting that it feels part of the tank’s
  4. 4. bonnethead community. To me it seems as though the sharks are loners, but in reality, they might feel “close enough” to one another and there may be a colony that is indeed thriving. When I asked a couple of the reef divers questions about the bonnetheads, their knowledge seemed somewhat limited to a general understanding of the animal. They were simply there to feed all the animals and to clean the tank. I was unable to meet a real bonnethead expert at the Shedd during my time of study; I was told that the people who could be considered experts were busy, and if I had any chance to interview them I would need to schedule appointments. However, the reef divers that I did talk to told me that the setting inside the reef exhibit is very rare, that is, female bonnetheads mingling in the same tank with a male bonnethead. At the time of my research none of the sharks had names, except for the male who had for unknown reasons earned the nickname Michael Jackson; although nothing had been formalized. In order to make observations run more smoothly I identified the three sharks based upon size, sexual organs, and a tag on one of the female’s left pectoral fin. The smallest of the three is the male and his body is full of high contrast black spots. For him, I used the name Michael Jackson (MJ). The largest of the three, female, and also the one carrying a tag, I named Bonnie. The female not quite as big as Bonnie and without a tag, I gave the name Savannah. In reference to the study done by Arthur A. Myrberg and Samuel H. Gruber, I used the term “completing the course” to be defined as the shark starting a patrol in the left corner of the tank, encircling the entire tank, which included reaching the right corner of the tank, and then returning back to the left corner of the tank. I also noted if there were divers in the tank at the time of the record and if feeding was occurring, had happened, or hadn’t yet happened. As they
  5. 5. patrolled, a term I have given to explain the simple behavior of swimming through the tank, they exhibited 15-20 different behaviors regularly; some behaviors more frequent than others. Each patrol that was recorded was done so using a standard stop watch and a journal to describe behaviors. I made the observations consecutively starting at random and in random orders. For example I would start the record at 10:30 AM. If Savannah swam to the left corner of the tank, I would begin recording her course until she had completed it. Whichever shark started a new course I would begin recording afterwards, it was entirely up to the sharks. If the course completion endured for longer than seven minutes this was recorded as longer than seven minutes as well as a did not complete course note attached. I defined seven minutes as the time threshold. Anything longer and it appeared to be irregular, as if the shark was preoccupied or distracted. Fortunately this was not a frequent occurrence and the sharks seemed to be patrolling in a regular pattern at all times of the day even with several variables; it’s as if they wanted to be studied. Nonetheless, it is my belief that the bonnetheads at the Shedd Aquarium have been influenced by the particular captive setting they are living in, and it has made them lone creatures, contrary to their typical highly social behavior. Review of Relevant Literature A previous study done by Arthur A. Myrberg and Samuel H. Gruber entitled The Behavior of Bonnethead Sharks, Sphyrna t. tiburo, has been the most informative and helpful in my pursuit of observing shark behavior. The study, published in 1974 by the journal Copeia, examined the behaviors of 10 bonnethead sharks held in captivity for six months. They were held in a somewhat natural condition and the purpose of the study was to record social patterns
  6. 6. and interactions within the group, if there were any, and their movements and postures and what they might indicate. They found that there is a definite social hierarchy, mostly based on size, and during the study they noted 18 patterns of movement that are believed to be relevant to social interactions. My own research did not have the same funding, facilities, or time but I did conduct a somewhat similar study. I was able to use a lot of the behavioral movements of the animals that are described in this study and apply them to my own study. It was interesting to see the three bonnetheads at the Shedd Aquarium exhibit the same behaviors as the bonnetheads from this research. Also in the study done by Myrberg and Gruber it seems as though they caught and studied more female bonnetheads than males, which may compromise some of their findings; they came to the conclusion from the gathered data that the sharks typically distanced themselves from larger males. On the Field Study of Shark Behavior from the publication American Zoologist, Donald R. Nelson discusses the problems faced with keeping these animals in captivity in order to observe them as well as problems associated with divers observing them in their natural habitats. This article from 1977 is a follow up to the aforementioned article, saying that although the work that Myberg and Gruber had taught the scientific community a lot, the science of studying shark behavior needs to be revamped to achieve a more natural state of observing the animal. This article interested me by its various descriptions of observing sharks in the wild, such as interactions between divers and sharks which are not an ideal way to study the animal because more often than not the dives include baiting, which automatically sets the animal into hunting
  7. 7. mode. This sort of forced observation is in my opinion similar to the divers who enter the tanks with the animals at the Shedd Aquarium in order to feed them and observe them. It induces behavior that is unnatural. Another concern that I’ve had in observing the animal, and the article directly confirms it, is studying the shark in a confined space, such as the Reef Tank at the Shedd is not exemplary of the animal’s natural behavior. The Signifigance of Parthenogenetic virgin mother in bonnethead sharks and mice, a case study conducted after two births occurred at the Henry Doorly Zoo in Nebraska. The article from Reproductive BioMedicine Online, published in 2007, confirms the incidence of multiple asexual births from female bonnethead sharks at the zoo. It was originally thought that the females which are capable of keeping intact spermatozoa for nearly six months had given birth to their young “traditionally,” but in fact the female sharks had been separated from any male bonnethead for several years, deeming that to be impossible. Furthermore, molecular studies soon found no evidence of paternal contribution within the young shark’s DNA, proving that the pup had only one parent. The article then continues, explaining how previously lab mice had also undergone parthenogenesis while being in captivity. This article contributes within the realm of strange capabilities of this species of shark. It makes me wonder if the female felt the need to procreate, as something instinctual, and if she had exhibited any odd behavior prior to and after giving birth. Interpreting the Blue Sharks at Underwater World published in December of 2002 in the Electronic Green Journal is extremely relevant and close to the type of observation I am
  8. 8. attempting. Although there are no Blue Sharks at the Shedd Aquarium, the essay by Ryder W. Miller cites the unnatural habitats these sharks live in at Underwater World in California, and their inability to adjust. She also poses questions that are uniformly applicable to all animals in captivity, such as “Would the shark be able to adapt to new conditions?” or “Would it learn to negotiate the turns in the thin tank?” In the end these sharks were not able to handle life in a holding tank habitat, so they were eventually released back into the wild. I have drafted a set of questions based on this article and its findings in captive Blue Sharks, and I plan to ask some if not all of the questions to the experts at the Shedd. The April 2008 article from the Journal of Fish Diseases, Three cases of gastric prolapse through the gill slit in sand tiger sharks, tells of three individual cases of captive sand tiger sharks undergoing natural stomach prolapse and eventually dying. The article suggests that being held in captivity was a major cause of the animals’ deaths. Data Collection From March 10, 2010 through April 19, 2010 I made observations of the three bonnethead sharks at the John G. Shedd Aquarium in Chicago, Illinois. The recorded observations, which were taken of each shark while “completing the course,” total up to fourteen. All other notes of behavior were taken in an informal standard, witnessed while not attempting to record a course completion. In the beginning of the study I marked each behavior
  9. 9. with a letter that had a corresponding definition. As time went on, I found it more helpful to describe the behaviors and later abbreviate them for quantitative summaries. The next few pages include the ethogram, which consists of the definitions of each behavior. Following that I have included examples of recorded course completions as well as the notes taken. Interpretation of Data Based upon my findings from recorded course completions and general observations it is unclear to me whether or not there is a complete group of bonnethead sharks at the Shedd Aquarium. That is a recognized social group that undeniably interacts with one another during events such as feeding and patrolling. The Shedd states that schools of bonnetheads typically exist when the numbers of sharks are between 5 and 15, and the majority of the schools are gender-specific. With that in mind, I do believe that the unnatural captive environment at the Shedd is deterring the animal’s characteristic nature of forming tight social groups. The majority of the time I witnessed the three sharks separated from each other, patrolling in a solitary manner. There wasn’t a single instance during course completions or not that I observed the bonnetheads patrolling together for more than one minute. All cases of feeding were done so alone, with one shark feeding while the others were off in other areas of the tank. The only instances of social formation I noticed were between male and female, and it was always MJ following one of the females. According to Myrberg and Gruber when a male follows a female it is likely to be in the interest of mating. On April 19, 2010 Bonnie was observed swimming on the right side of the tank away from the other sharks. She remained in that area, engaging in a cycle of breaking the surface
  10. 10. near the upper portion of the right rock, turning back towards the remainder of the tank and then breaking the surface once again as she turned back in the direction of the right rock. She continued to behave like this for at least 15 minutes and it was one of the rare times she did not complete the course. At the time the yellow weight that indicates to the bonnetheads that it is feeding time was in the water. Not only did she avoid the tongs that held the squid she was intended to eat, but she avoided the left side of the tank. It is important to note that at this moment there was a noticeably large crowd surrounding the glass on the left side of the tank, banging against the glass and yelling amongst each other. I believe the loud group of spectators standing just outside the tank affected Bonnie’s desire to feed as well as patrol the tank like the bonnetheads are typical of at the Shedd. However, this was one of the only times I detected crowd levels at the exhibit as a factor determining the sharks’ behavior. What further research logically follows? As I first entered the viewing area of the Caribbean Reef exhibit at the Shedd Aquarium the first thing I noticed was the groups of city school kids running around, playing tag, banging their hands against the glass, and screaming “there’s a hammerhead, there’s a great white!” Neither of the two aforementioned sharks are in the exhibit, but there is a group of bonnethead sharks. When I first laid eyes on these beasts, the largest being Bonnie at only 4½ feet long, I thought “All they are doing is swimming in circles, how am I going to research this?” I scrambled, trying to decipher whether or not I had chosen an appropriate research subject. It wasn’t until I came across the study done by Myrberg and Gruber that my project evolved from the idea of hanging out at the Shedd Aquarium among sharks to a full-fledged ethological study. After studying the techniques and methods of these two ethologists my own work continued
  11. 11. progressing through the weeks and along the way I dreamt up future research that should be done if not to validate the points of prior research then to explore different routes of ethological study. As time went on I came to the conclusion that anyone could conduct the research that I was doing. If you have $80 to cover the membership fees, a pen and paper, and a stop watch then the Caribbean Reef is yours and the sharks, rays, turtles, and other fish are there waiting to be studied. What could set my research apart from this informal viewing is the element of access. What my study lacks is my inability to access the reef from different perspectives, such as above, on top of the feeding platform, or in the water, or even to observe at night. Further research would include a more diverse set of variables such as lessening the population density of the tank to better focus in on the bonnetheads, perhaps they are overwhelmed by the crowded conditions of the reef exhibit. Undoubtedly more time to conduct the study would be necessary in order to test the validity of the behaviors I have identified. This would insure that the behaviors were not exclusive to the time that I had observed them. With the extension of time may also be additional observable behaviors as well as the opportunity to see what impact the addition of MJ the male has on the bonnethead colony and how they adapt. Most importantly, with extra time I would analyze more thoroughly the potential of an established social group between the bonnetheads. Furthermore, the aspiration of the staff at the Shedd Aquarium is to hopefully encourage breeding among the bonnetheads, thus the imputation of the male. A subsequent study during the months of pregnancy and after birth would be something I would likely pursue.
  12. 12. References 1. Myrberg, A.A. Gruber S.H. (1974). The Behavior of Bonnethead Sharks, Sphyrna tiburo. Copeia, (2), 358-374. 2. Nelson, D.R. (1977). On the Field Study of Shark Behavior. American Zoologist, 17(2), 501- 507. 3. Edwards, R.G. (2007). The Signifigance of Parthenogenetic virgin mother in bonnethead sharks and mice. Reproductive Biomedicine Online, 15(1), 5-12. 4. Miller, R.W. (2002). Interpreting the Blue Sharks at Underwater World. Electronic Green Journal, 1(17), 1-8. 5. Tuttle, A.D., Burrus, O., Burkart, M.A., Scott, P.W., Stoskopf M.K., Harms, C.A. (2008). Three cases of gastric prolapse through the gill slit in sand tiger sharks. Journal of Fish Diseases, 31, 311-315. 6. Klimley, P.A. (2003). The Secret Life Of Sharks. New York: Simon & Schuster. 7. Bonnethead Sharks. Shedd Aquarium. 8. Johnson, A. Lincoln Park Zoo: Pied-Tamarins.
  13. 13. Ethogram SUG=Swim up against glass (24) P=Swim down into pit (21) TB=Turnback (14) SUMR= Swim up against middle rock (14) BS=Break Surface (13) G=Gaveway to other fish (12) S=Streamline (11) UC= Uninterrupted Cycle (9) E=Evade (7) F= Following (5) JS= Jaw Snap (5) SULR=Swim up against left rock (5) GS=Gaveway to other shark (5) FS=Followed small fish (5) L=Leading (4) SURR=Swim up against right rock (4) JSH=Jaw Shake (3) SDG=Swim down against glass (3) --Number indicates how many times behavior was observed; limited to course completion records only-- * It should be noted that due to large crowds and inability to see from certain angles, the sharks did drift out of sight from time to time.
  14. 14. Behavior Definitions A total of 18 behaviors were regularly observed based upon their regular occurrence. Other behaviors were observed and noted in the records but these were observed only once or on rare occasions. 1. Swimming up against glass- Shark would approach glass swim up against it until it reached the top. It would then turn in either direction. 2. Swimming into the pit- The sharks were often observed swimming into the pit, or the section of the exhibit where there was no artificial reef, only a rock bottom. They were never seen spending an absorbent amount of time down there. 3. Turnback- Instantly turning away from the initial direction of travel. 4. Swim up against middle rock- This behavior was seen often when there was a diver in the tank. The shark would approach the middle rock, which reaches to the floor, and swim up against it. It was rare that this behavior did not occur as part of a cycle. 5. Break surface- Shark would swim towards the surface and break the surface of the water; often seen while swimming up against the glass. 6. Gaveway to other fish- Shark would be swimming towards an approaching fish and the shark would avoid the fish while the fish maintained its course. 7. Streamline- The shark would quickly accelerate and then directly after body movement would stop while it glided forward through the water; often seen after avoiding another tank occupant. 8. Uninterrupted cycle- This behavior was noted when the shark completed the course rather quickly with little to none other behaviors being observed. 9. Evade- The shark would quickly and suddenly accelerate, swimming away in order to avoid another other fish. 10. Following- Shark would alter present course in order to closely follow other shark, mimicking the other shark’s movements. The following was often brief. 11. Jaw snap- Shark opens and then snaps jaw shut; food is not present. 12. Swim up against left rock- Shark swims up and against the left rock, usually turning towards the remainder of the tank. 13. Gaveway to other shark- Two sharks swimming towards each other and one shark swims away from the other while the other shark maintains its course.
  15. 15. 14. Followed small fish- Shark would follow smaller fish, at times brushing the small fish with its head. 15. Leading- Led other shark as it patrolled the course, like the following behavior it was brief. 16. Swim up against right rock- Shark swims up and against the right rock, then turns towards the remainder of the tank. 17. Jaw Shake- The shark would shake its head from side to side for short period of time. 18. Swim down against glass- Unlike swimming up against the glass, this behavior was only observed three times during recorded course completions. This behavior was seen when the shark was swimming along the glass and would quickly swim down towards the bottom of the tank, against the glass. *It’s important to note that behaviors cannot be automatically linked with emotions, significant evidence must be presented before we can make that assumption about an animal’s thought process, i.e. while witnessing the behavior evade, one should not make the assumption that the animal is fearful of some variable, or that it feels in danger.
  16. 16. Averages Averages are compiled based on the group’s exhibition of each behavior, not animal by animal. I feel as though this explores the possibility that the sharks are behaving as a group. These numbers were computed by totaling the time of recorded course completions and then dividing the number of times a behavior was exhibited by the total time. What this shows is roughly how often during a patrol the colony of sharks displays each behavior. Behavior Average Swim up against glass 20% Swim down into pit 18% Turnback 12% Swim up against middle rock 12% Break Surface 11% Gaveway to other fish 10% Streamline 9% Uninterrupted Cycle 8% Evade 6% Following 4% Jaw Snap 4% Swim up against left rock 4% Gaveway to other shark 4% Followed small fish 4% Leading 3% Swim up against right rock 3% Jaw Shake 2.5% Swim down against glass 2.5%
  17. 17. Reef Exhibit Layout Left Rock Middle Rock Right Rock Artificial reef lies along the perimeter of the tank, adjacent to the glass. Viewing Area Pit Viewing Area