Abstract

Marine mammal stranding networks are the cornerstone for the surveillance of morbidity and mortality in these legally protected wildlife populations. Among many things, the contributions of this largely volunteer-based network establish baseline patterns of marine mammal strandings and thus detect perturbations in the magnitude or nature of stranding events. As sentinels of the aquatic ecosystems in which they live,^1,2 marine mammals provide an important avenue for the investigation of ocean and human health. In 1991, NOAA established the process by which marine mammal unusual mortality events (UMEs) were recognized, which allocated additional scientific expertise and resources to their investigation. Title IV of the Marine Mammal Protection Act (MMPA) formalized the NOAA Fisheries Marine Mammal Health and Stranding Response Program in 1992 and mandates that NOAA and the US Fish and Wildlife Service (USFWS) investigate marine mammal UMEs.

Since 1991, the number of UMEs declared per year has steadily increased, which may reflect a true increase in mortality events, an increase in surveillance, or both.³ To date, there have been 55 formally declared UMEs that have spanned all major coastal regions.⁴ Cetaceans and pinnipeds comprise 81% of all species impacted, though manatees, sea otters and walrus have also been involved. While the cause of more than half (53%) of the declared UMEs has been undetermined, trends have emerged.⁴ From 1991–2000, infectious disease dominated the determined causes of UMEs, but more recently, biotoxins have enumerated many more of these events.^4-6

The determination and investigation of UMEs in the U.S. relies heavily on the expertise of aquatic animal health professionals. When a mortality event is suspected, NOAA or USFWS undertakes a consultation with the Working Group on Marine Mammal UMEs, a diverse panel of voluntary experts from a variety of specialized fields. Once NOAA or USFWS officially declare a UME, a team is formed and leaders are identified to carry out the investigation under the guidance of the Working Group. This Investigative Team is responsible for stranding response, animal care, sample collection and diagnostic evaluation. The Working Group and Investigative Team supply expertise across related fields, including biology, pathology, microbiology, toxicology and epidemiology and collaborate to identify the cause of the event, its impact on the population(s), its relationship to environmental variables, and future research needs. Aquatic animal health professionals engaged in the care and welfare of captive marine mammal collections can be a unique asset to these investigations and may lend innovative suggestions to the formulation of differential diagnoses, guide diagnostic planning and treatment, and inform sample collection and human health protocols. Information from captive animals for comparisons may help elucidate abnormalities. The new information gleaned from UMEs may help guide population management efforts, facilitate future stranding preparedness and inform preventive medicine for captive populations.

Acknowledgements

The authors thank all members of the Marine Mammal Stranding Network, and the past and present members of the Working Group for Marine Mammal Unusual Mortality Events.

References

1.  Bossart GD. Marine mammals as sentinel species for oceans and human health. Vet Pathol. 2011;48(3):676–690.

2.  Moore SE. Marine mammals as ecosystem sentinels. J Mammal. 2008;89(3):534–540.

3.  Gulland FMD. Review of the Marine Mammal Unusual Mortality Event Response Program of the National Marine Fisheries Service. U.S. Department of Commerce, NOAA Tech. Memo. NMFS-OPR-33. 2006:37.

4.  NOAA Fisheries Office of Protected Resources Marine Mammal Health and Stranding Response Program www.nmfs.noaa.gov/pr/health/mmume

5.  Gaydos JK. Bottlenose dolphins and brevetoxins: a coordinated research and response plan. U.S. Department of Commerce, NOAA Tech. Memo. NMFS-OPR-32. 2006:46.

6.  Gulland FMD. 2000. Domoic acid toxicity in California sea lions (Zalophus californianus). Report to the National Marine Fisheries Service Working Z group on Unusual Marine Mammal Mortality Events. U.S. Department of Commerce, NOAA Tech. Memo. NMFS-OPR-17.