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Research Study Reveals Dolphins in U.S. Aquariums and Zoos Live As Long As or Longer Than Dolphins in the Wild
Grassy Key… Bottlenose dolphins living in United States marine mammal facilities live as long as, or longer than, dolphins in the wild according to a new research study published today in the journal Marine Mammal Science. (K. Jaakkola/K. Willis: How long do dolphins live? Survival rates and life expectancies for bottlenose dolphins in zoological facilities vs. wild populations. Marine Mammal Science 2019; DOI: 10.1111/mms.12601.) Analyzing close to 40 years of data from a U.S. government source called the Marine Mammal Inventory Report (MMIR), researchers determined that the current median life expectancy of bottlenose dolphins in U.S. facilities is 29.2 years. The study also compared the MMIR data with previous studies of three different wild populations of dolphins. In each comparison, the average life expectancy of dolphins in facilities was shown to be equal to or greater than that of dolphins in the wild.
Dr. Kelly Jaakkola of Dolphin Research Center, and Kevin Willis of The Minnesota Zoo, co-authored the peer-reviewed study. “Survival rates and life expectancies are indicators of overall health and well-being,” explained Dr. Jaakkola. “Critics of zoos and aquariums will frequently claim that dolphins in facilities don’t live as long as dolphins in the wild, in an attempt to influence public opinion and even proposed legislation. This study shows that that claim is just not true.”
To determine the median life expectancy of dolphins in U.S. facilities, Jaakkola and Willis divided the MMIR data into four time periods of about ten years each, and applied the Kaplan-Meier Survival Analysis to the data. This enabled them to calculate annual survival rate and median life expectancy over historical time. Life expectancy is the average number of years that animals in a population are expected to live, while life span identifies the maximum number of years that animals in a population can live. “In humans, for example, the maximum lifespan so far is about 122 years, whereas average life expectancy worldwide is about 72 years,” said Jaakkola.
The last scientific paper to analyze survival of dolphins in marine mammal facilities used data that are now more than 25 years old. “Even back then, their life expectancy was increasing,” Jaakkola continued. “We thought it was important to do a new study to update those results – to see if dolphin life expectancy had continued to increase, and to compare the results to wild populations.”
For complete data sets like the MMIR, a survival analysis like the Kaplan-Meier is the best mathematical approach. Unfortunately, due to the more limited observations inherent in studies of wild populations, no wild study to date has been able to use this type of analysis. Instead, previous studies used different analyses to study the wild dolphin populations of three different areas: the Indian River Lagoon System, FL (1978-1997); Mississippi Sound Region (1986-2003); Sarasota Bay, FL (1980-1987). For an accurate comparison to these studies, the Jaakkola/Willis study used the same analysis method on the MMIR data that was used for each of the different wild populations. In every case, the median life expectancy of dolphins living in U.S. facilities today was found to be as long or longer than their wild counterparts.
Article text is available with open access at: http://doi.wiley.com/10.1111/mms.12601
Founded in 1984, Dolphin Research Center is a nonprofit organization, and home to bottlenose dolphins and California sea lions. Located at 58901 (mile marker 59) Overseas Highway, Grassy Key, Florida, the center is open daily for the public to see narrated behavior sessions and educational presentations, and to participate in interactive programs. The center is funded by admission and program fees as well as by private donors and members. In addition to being one of the most highly respected education and research facilities in the world, DRC is an accredited member of the Alliance of Marine Mammal Parks and Aquariums and the International Marine Animal Trainers Association. For more information, visit www.dolphins.org.