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What Happened to the Dolphins?

Module by: Sarah Burkett. E-mail the author

Summary: This case study is based on the 1978 – 1988 Bottlenose dolphin die-offs along the Atlantic coast of the U.S. It demonstrates nature of science, as new information evolved theories change. New observations lead to more sophisticated inferences, as more observations are carefully recorded, better inferences can be made.

Figure 1
Figure 1 (graphics1.jpg)
Taylor was returning home to Jacksonville, Florida after a brief trip to Panama City located in the Florida panhandle. At last, it is hurricane season! The tropical storms that come through provide the best waves for surfers. Last weekend there just so happened to be a category 3 tropical storm brewing in the Gulf of Mexico, stirring things up beautifully. Taylor could not believe he was being forced to cut the best weekend of his life, so as to be back in time for school on Monday. His mother was pleased he made it home in time for their family dinner on Sunday night. While discussing his amazing weekend in Panama City, Taylor is suddenly drowned out by the increased decibel of the six o’clock news report; BREAKING NEWS- “A considerable amount of Bottlenose Dolphins have washed ashore dying and/or already dead along the Atlantic coast from New Jersey to Florida. More on this after our break…”

We all looked at one another stunned! We had just swam with the dolphins a few weeks back. During my school spring break my family and I took a trip to Discovery Cove in Orlando, Florida. Where we formed a relationship with a Dolphin named Echo. Echo let us pet him, gave us kisses, played fetch and took us for a ride on his dorsal fin. We learned all about Dolphins and their habitat that day. The news was back on…

“A government investigation is underway to find the cause for this unusual increase in mortality. Researchers preliminary results suggest that the red tide found off the coast of Cape Hatteras may have caused this extraordinary rise in dolphin fatalities. We will continue to keep you updated as this story unfolds. In other news…”

In biology class the following day Taylor’s instructor informed them that the total number of deaths thus far was around 150. Additionally, red tide is the more commonly used name for an algae bloom. Algae blooms can occur both naturally or as the result of human pollution through various means. Typically, “red tide” only affects fish, birds, and shellfish. Interestingly, die-offs of these species do not coincide with the up rise in dolphin mortality. Investigators initial findings indicate irregularities in the lungs and lymph nodes that are not typically associated with red tide.

By the end of the season some 742 dolphins’ deaths were recorded along the Atlantic coast. Due to the fact that not all dolphins that die at sea washed ashore, it is estimated that approximately 2,500 dolphins perished during this tragedy. This represents more than one half of the inshore population within the affected area.

Figure 2
Figure 2 (graphics2.png)
The map above of the United States displayed in red, represents the Eastern coast. Along the coast line is where the dolphins were washing ashore.

Figure 3: Figure 3 is of a healthy Bottlenose Dolphin.
Figure 3 (graphics3.jpg)
Figure 4: displays red tide off the coast of N. Carolina.
Figure 4 (graphics4.jpg)

If you were going to solve the mystery and discover what the cause for this unusual increase in dolphin mortality was, what information might you require? Why?

Fact Sheet

Although red tide was present in Cape Hatteras, North Carolina in October 1987, no red tide was evident when increased mortality began in New Jersey that June. Additionally, the assay used to identify brevetoxin was found to be unreliable in the early 1990. The lesions found on the dolphins are uncharacteristic of bevetoxin. Instead they are representative of bacterial and fungal infection. Polymerase Chain Reaction (PCR) testing detected morbillivirus RNA in 35 / 36 Dolphins tested. Findings in 1997 support morbillivirus as the primary cause of death. The 1997 study also found that tissue samples containing the morbillivirus also contained secondary infections. Primarily phenomia, many of which were backterial, fungal or mixed. The overall finding of the study suggests that because of the immunosuppressive effects of the morbillivirus the dolphins were unable to fight off secondary infections. Findings from a 1999 publication by Schulman suggest that the die off isn’t related to sex, age, geography, or month due to the unanimous representation of findings. Research is being conducted on wheather exposure to environmental pollutants such as polychlorinated biphenyls (PCB), dioxins and furans, polyaromatic hydrocarbons and certain heavy metals decreases the mammals resistance to infection.

Teacher Directions for Students

  • Tell students they will receive a copy of a case they are to individually read.
  • Upon completion, they will assemble into groups of four or five to discuss the question.
  • After, someone from each group will share what their group came up with.
  • Groups will be given a fact sheet to read. They will be given a few more minutes to discuss the new information and come up with a theory to explain what happened to the dolphins.

Procedure for Implementing Case

Teachers should have students read the story “What Happened to the Dolphins” individually. Once everyone has finished instructor will assemble students into group of four or five. It is the groups’ task to come up with some ideas and brainstorm about information they might require to discover what caused the unusual increase in dolphin casualty. After about five minutes group discussions will end. A representative from each group will present their collective thoughts on the situation one at a time. After all the groups have spoken, the instructor will distribute fact sheet for each student to read over.They will then discuss their new findings within their group. Groups will reconvene for about five minutes. A spokesperson from each larger group will inform others what the general consensus for the group was. What was their theory for the dolphin mortality. If they are unable to reach a consensus then a member from each side should debate their point and tell why they disagreed with the rest of their group.

Side Note

Effective classroom management and procedures for transition are critical to the success of this activity. Students must receive directions before the case is passed out.

Concluding Arguments

From June of 1987 to May of 1988 approximately 2,500 bottlenose dolphins perished along the eastern coast of the U.S. Results of a scientific investigation concluded that the most likely cause was brevetoxin also known as “red tide.” However, this theory is controversial. Although red tide was present in Cape Hatteras, North Carolina in October 1987, no red tide was evident when increased mortality began in New Jersey that June. The lesion found on the dolphins are uncharacteristic of bevetoxin.Instead they represented bacterial and fungal infection. Additionally, the assay used to identify brevetoxin was found to be unreliable in the early 1990. Other government sponsored studies concluded morbillivirus to be the leading cause of death. Through Polymerace Chain Reaction (PCR) testing morbillivirus was found in 35 of 36 dolphins tested.Research is being conducted on wheather exposure to environmental pollutants such as polychlorinated biphenyls (PCB), dioxins and furans, polyaromatic hydrocarbons and certain heavy metals decreases the mammals resistance to infection. Findings from Table 1 in 1997 support morbillivirus as the primary cause of death.

Figure 5
Figure 5 (graphics6.png)

  • Diaz, A. “red tide” photograph. 2005. Retrieved 15 April 2009
  • Jeffery K. Taubenberger, J. Mark Tsai, Amy E. Krafft, Ph.D., Jack H. Lichy, M.D., Ph.D., Ann H. Reid, M.A., F. Yvonne Schulman, D.V.M., and Thomas P. Lipscomb, D.V.M. Dispatches. Emerging Infectious Diseases. Vol. 2, No. 3—July-September 1996. Retreived 10 March 2009 from academic search premier
  • Luebke, B. Ph.D. EDRI Federal Project Inventory: Evaluation of Immune Function, Chemical Exposure and Morbillivirus Infection In Bottlenose Dolphins from Clean vs Polluted Costal Waters. March 2nd, 2006. EPA. Retrieved 15 April 2009 from http://www.epa.gov/edrlupvx/inventory/ETD-LUB1.html
  • NASA. Bottlenose Dolphin. 2007. Retrieved 27 March 2009 from http://en.wikipedia.org/wiki/File:Bottlenose_Dolphin_KSC04pd0178_head_only.JPG
  • Schulman, F. and Lipscomb, T. Dermatitis with Invasive Ciliated Protozoa in Dolphins That Died During the 1987–1988 Atlantic Bottlenose Dolphin Morbilliviral Epizootic. Vet Pathol 36:171–174 (1999). Retreived 10 March 2009 from academic search premier.
  • U.S. map East Coast.2007. Retrieved 15 April 2009 from http://images.google.com/imgres?imgurl=http://upload.wikimedia.org
  • Zinkova, M. A Surfer at the Wave. 2007. Retrieved 15 April 2009 from http://en.wikipedia.org/wiki/Surfer.

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