Assessing the Health of the Dolphin Population at the U.S. Navy Marine Mammal Program: 1987-2007
The U.S. Navy Marine Mammal Program (MMP) houses and cares for a population of bottlenose dolphins (Tursiops truncatus). In recent years, MMP dolphin care needs have changed due to the presence of an active breeding program, increasing numbers of geriatric dolphins aged greater than 40 years old, and increased, long term deployments involving more animals. As a result, the MMP strives to continually improve its preventive medicine, clinical medicine, and advanced diagnostics programs. To better understand recent population changes and the MMP's ability to maintain dolphin health, we assessed population age structures, median survival age, survival rates, and age-specific mortality rates for the years 1987-2007. In 2007, the median dolphin age was 24.1 years (range 0-50), 9.6% of dolphins were aged at least 40 years old, and 13.7% were aged no more than 5 years old. During 2002-2007, the median survival age was 27, the survival rate was 0.98, and mortality rates for dolphins aged >30 days-5 years, > 5-20 years, and >20-40 years were 2.6%, 1.8%, and 2.3%, respectively. Compared to 1987-2001, the mortality rate for dolphins aged > 5 to 20 years decreased significantly (P < 0.05). In comparison, previously reported results from managed collection dolphin populations in 1990 were a median survival age of 17, a mean survival rate of 0.93, and a crude mortality rate of 7%.1-3 This study demonstrates that the MMP has maintained and improved the health of its dolphin population to levels better than previously reported for collection dolphin populations in 1990. Updated analyses are needed to assess similar improvements in other managed dolphin populations since 1990, and more data are needed from wild dolphin populations to enable proper comparisons with the MMP.
The authors wish to thank the management team and animal care staff at the U.S. Navy Marine Mammal Program (MMP) for their outstanding efforts in supporting and caring for animals at the MMP.
1. Asper E.D., L.H. Cornell, D.A. Duffield, and N. Dimeo-Ediger. 1988. Marine mammals in zoos, aquaria and marine zoological parks in North America: 1983 census report. International Zoo Yearbook 27: 287-294.
2. Asper E.D., D.A. Duffield, N. Dimeo-Ediger, and E.D. Shell. 1990. Marine mammals in zoos, aquaria and marine zoological parks in North America: 1990 census report. International Zoo Yearbook 29: 179-187.
3. DeMaster D.P. and J.K Drevenak. 1988. Survivorship patterns in three species of captive cetaceans. Marine Mammal Science 4:297-311.