May 2, 2019
Frequent contributor to Zoo Logic, Dr. Kelly Jaakkola, Director of Research for the Dolphin Research Center discusses the new peer-reviewed study she coauthored and published in the Journal Marine Mammal Science that compared survival rates and life expectancies for bottlenose dolphins living in zoological facilities with comparable values published for wild populations. The main takeaway from the study is dolphins living in zoological facilities today live at least as long or longer than wild populations studied to date. These results stand in stark contrast to some zoo and aquarium critics that continue to promote the false claim that dolphins do not live as long in human care.
Data analyzed in this new study come from a U.S. government source called the “Marine Mammal Inventory Report” (MMIR), which lists basic information (e.g. birth date, death date, transfers, etc.) for all dolphins in marine mammal facilities in the U.S over the past 40 years or so.
A few complications with comparing current MMIR data with previous studies of wild populations are due to the inherent limited scope of observations found in most wild studies and the different methods of statistical analysis that have been used in each previous publication. To make comparisons valid, the new study used the same analysis on the MMIR data that was used for each wild population publication.
The last scientific paper to analyze survival for dolphins in facilities before this latest study used data that are now more than 25 years old. Even back then, survival rate and life expectancy for dolphins living in zoos and aquariums in the US were increasing and this study shows continuing significant increases since then.
The current median life expectancy of bottlenose dolphins living in human care in the U.S. is 29.2 years. This is based on the most robust method of analysis called the Kaplan-Meier Survival Analysis. While the K-M approach is the most accurate analysis because it uses information from ALL animals in the population (both dead and living) and does not assume equal probability of dying at all ages like some of the other methods used in previous publications require, no wild study has yet used the Kaplan-Meier method to analyze the life expectancy of the respective wild populations examined due to the lack of detailed information on the age of living animals and the age-at-death for dead animals.
Also of interest was the finding that a direct comparison of calf survival rate between the decades-long field study of the Sarasota population of dolphins and modern MMIR data found no significant difference between populations. In other words, while dolphin calf (age less than 1 year) mortality is higher than for adults, as is the case for many species including humans, there is no significant difference in survival rate between dolphin calves born in human care and those born in the wild.
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. Available at: http://doi.wiley.com/10.1111/mms.12601