An understanding of the causes of morbidity and mortality in killer whales can inform policy decisions and conservation actions. The Southern Resident killer whales are an endangered population of fish eating whales that reside in Salish Sea. Their known environmental concerns include contaminants, nutritional stress, increased underwater noise, and infectious and parasitic disease. How these challenges are reflected in population health and recovery is an important question to be answered. Current resources in killer whale health include published studies on mortality of captive killer whales1, stranding trends of free ranging whales2 and identification of infectious agents of concern for the species3,4.
To enhance information on killer whale health, we reviewed pathology reports from killer whales that stranded in the eastern Pacific over the 10 year period from 2004 until 2013. Cases were further classified into three age groups - calf, sub-adult, and adult. Each case was evaluated by a team of pathologists to categorize the cause of death and concurrent concerns. There were 53 cases extending from Alaska to California and including Hawaii. Twenty-two cases (42%) had sufficient information to determine a probable or confirmed cause of death. Cases included seven calves composed of two cases with infectious causes - one from a hook injury and one case of salmonellosis likely from omphalitis, two mortalities related to a failure of passive transfer and three cases attributed to nutritional issues - two related to congenital concerns and one that may have been either a premature delivery or a case of placental insufficiency. Causes of death for six sub-adult animals included trauma for 3 animals, nutritional for two animals and one death attributed to infectious concerns associated with peritonitis. Nine adult deaths were classified with three mortalities due to infectious concerns, four due to metabolic issues resulting from environmental incidents and two due to traumatic events. Human interaction cases were found in every age class: 1 calf, two sub-adults, and two adults.
The equal balance of concerns across age classes was a surprising result. Most likely, it reflects the small sample set. As the case numbers grow, the necropsy results from stranded killer whales will undoubtedly reveal the changing health threats to this species across both age classes and sub populations. In 2004, a comprehensive necropsy protocol enhanced the collection of necropsy data from killer whales to identify concerns causing morbidity and mortality. The beneficial impacts of this protocol are just being realized.
The authors wish to thank the extensive list of biologists, veterinarians, stranded animal response personnel that contributed to the investigations of all of these cases. Without their hard work, none of this would be possible.
* Presenting author
1. Ridgway SH. Reported causes of death of captive killer whales (Orcinus orca). J Wildl Dis. 1979;15(1):99–104.
2. Barbieri MM, Raverty S, Bradley Hanson M, Venn-Watson S, Ford JK, Gaydos JK. Spatial and temporal analysis of killer whale (Orcinus orca) strandings in the North Pacific Ocean and the benefits of a coordinated stranding response protocol. Marine Mammal Science. 2013;29(4):E448–E462.
3. Gaydos JK, Balcomb KC, Osborne RW, Dierauf L. Evaluating potential infectious disease threats for southern resident killer whales, Orcinus orca: a model for endangered species. Biological Conservation. 2004;117(3):253–262.
4. Colegrove KM, St. Leger JA, Raverty S, Jang S, Berman-Kowalewski M, Gaydos JK. Salmonella Newport omphaloarteritis in a stranded killer whale (Orcinus orca) neonate. J Wildl Dis. 2010;46(4):1300–1304.