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Transcript of Bonnethead Shark

John G. Shedd Aquarium

The Bonnethead Shark in Captivity

Researcher: Nicholas Brandt

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 animals 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

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 animals 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 sharks 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 sharks behavior suggesting that it feels part of the tanks

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 females 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 hadnt yet happened. As they

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; its 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

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 Zoolog