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Evaluation of population health among bottlenose dolphins (Tursiops truncatus) at the United States Navy Marine Mammal Program

Stephanie K. Venn-Watson DVM, MPH1, Eric D. Jensen DVM2, and Sam H. Ridgway DVM, PhD, DACZVM3
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  • 1 National Marine Mammal Foundation, 2240 Shelter Island Dr, San Diego, CA 92106.
  • | 2 US Navy Marine Mammal Program, 53560 Hull St, San Diego, CA 92106.
  • | 3 National Marine Mammal Foundation, 2240 Shelter Island Dr, San Diego, CA 92106.

Abstract

Objective—To evaluate health indicators for a population of bottlenose dolphins in the US Navy Marine Mammal Program (MMP) by use of data acquired from 1988 through 2007.

Design—Retrospective cohort study.

Animals—167 bottlenose dolphins.

Procedures—The following indicators were used to evaluate the health of dolphins during the 20-year period: 5-year age structure, median survival age, annual survival rates, mortality rates, and neonatal and calf survival and mortality rates. Limitations of these population measurements as health indicators for dolphins were assessed.

Results—Crude mortality rates of dolphins for 1988 through 1992, 1993 through 1997, 1998 through 2002, and 2003 through 2007 were 3.1%, 4.7%, 3.6%, and 2.4%, respectively; during these same 4 study periods, median survival ages were 14.3, 14.4, 17.7, and 26.1 years, respectively, and mean survival rates were 0.98, 0.97, 0.97, and 0.99, respectively. From 1988 through 1997, 1998 through 2002, and 2003 through 2007, neonatal mortality rates were 4 of 16, 5 of 20, and 2 of 14 neonates, respectively. During these 3 study periods, mean annual survival rates for calves < 3 years old (excluding neonates that died at < 30 days old) were 0.97, 0.92, and 0.99, respectively.

Conclusions and Clinical Relevance—Although there were limitations to the measurement of some health indicators, use of multiple methods indicated that the health of dolphins in the MMP population was comparable to, if not better than, that published for other dolphin populations. The MMP population of dolphins may provide useful reference values of health indicators for use in assessment of other managed dolphin populations.

Abstract

Objective—To evaluate health indicators for a population of bottlenose dolphins in the US Navy Marine Mammal Program (MMP) by use of data acquired from 1988 through 2007.

Design—Retrospective cohort study.

Animals—167 bottlenose dolphins.

Procedures—The following indicators were used to evaluate the health of dolphins during the 20-year period: 5-year age structure, median survival age, annual survival rates, mortality rates, and neonatal and calf survival and mortality rates. Limitations of these population measurements as health indicators for dolphins were assessed.

Results—Crude mortality rates of dolphins for 1988 through 1992, 1993 through 1997, 1998 through 2002, and 2003 through 2007 were 3.1%, 4.7%, 3.6%, and 2.4%, respectively; during these same 4 study periods, median survival ages were 14.3, 14.4, 17.7, and 26.1 years, respectively, and mean survival rates were 0.98, 0.97, 0.97, and 0.99, respectively. From 1988 through 1997, 1998 through 2002, and 2003 through 2007, neonatal mortality rates were 4 of 16, 5 of 20, and 2 of 14 neonates, respectively. During these 3 study periods, mean annual survival rates for calves < 3 years old (excluding neonates that died at < 30 days old) were 0.97, 0.92, and 0.99, respectively.

Conclusions and Clinical Relevance—Although there were limitations to the measurement of some health indicators, use of multiple methods indicated that the health of dolphins in the MMP population was comparable to, if not better than, that published for other dolphin populations. The MMP population of dolphins may provide useful reference values of health indicators for use in assessment of other managed dolphin populations.

Contributor Notes

The authors thank Dr. Cynthia Smith, Dr. Mark Xitco, and Mike Rothe for technical assistance.

Address correspondence to Dr. Venn-Watson (stephanie@epitracker.com).