The mortality of marine mammals, including the California sea lion (Zalophus californianus), is caused by a variety of natural and anthropogenic causes such as malnutrition, predation, illness and trauma.3,4 In the west coast of Isla Magdalena (Baja California Sur, Mexico), a large amount of dead marine mammals are regularly washed ashore, mostly due to the coast configuration, winds and sea currents.2,5 The objective of this study was to investigate the causes of death of sea lions found dead along the west coast of Isla Magdalena. During 32 consecutive days in May and June 2012, necropsies were performed on all the dead sea lions (n = 19) found, and samples were collected for histopathology, immunohistochemistry and microbiology. Of all the animals investigated, 11 were male, 7 female, and the gender could not be determined in one case due to severe predation. Fourteen of these animals were juvenile, 1 was sub-adult, and 4 were adult. The causes of death were: cranial trauma 42%, cancer 5.2% and pneumonia 5.2%. The cause of death could not be determined in 47% of the cases due to advanced autolysis. PCR for Leptospira spp., Brucella spp. and Morbillivirus were performed on samples of the 4 freshest carcasses (liver, kidney, lung and brain). Three out of the four cases were positive to Leptospira spp., but none tested positive for Brucella spp. or Morbillivirus. This study revealed a high incidence of cranial trauma (42%), most likely of anthropogenic cause. Although PCR was positive for Leptospira spp. in 3 cases no lesions suggestive of this disease were seen in any of these animals, which suggest that they were asymptomatic carriers and detection of Leptospira spp. was an incidental finding. Leptospira spp. has been found before in clinically healthy sea lions.1 The high degree of decomposition had an important role in the lack of cause of death determination, which occurred in 47% of the cases.
The authors thank Drs. Efrén Díaz, Rene Torres, Rosa Elena Sarmiento, Liliana Suárez, Beatriz Arellano and Rosalía Ávalos for their help. The authors thank CONACYT and SIP for financial support. The help of the California Animal Health and Food Safety lab (UCDavis) and the Laboratory of Morphophysiology (CICIMAR - IPN) is also appreciated.
* Presenting author
1. Acevedo-Whitehouse K, De la Cuevas H, Gulland FMD, Aurioles-Gamboa D, Arellano-Carbajal F, Suarez-Güemes F. Evidence of Leptospira interrogans infection in California sea lion pups from the Gulf of California. J Wildlife Dis. 2003;39(1):145–151.
2. Geraci JR, Lounsbury VJ. Marine Mammals Ashore: A Field Guide for Strandings. Texas: Texas A&M University Sea Grant College Program; 1993.
3. Geraci JR, Harwood J, Lounsbury VJ. Marine mammals die-offs. In: Twiss JR, Reeves RR, eds. Conservation and Management of Marine Mammals. Washington, DC: Smithsonian Institution Press; 1999:363–395.
4. Kovacs KM, Aguilar A, Aurioles D, Burkanov V, Campagna C, Gales N, Gelatt T, Goldsworthy SD, Goodman SJ, Hofmeyr GJG, Härkönen T, Lowry L, Lydersen C, Schipper J, Sipilä T, Southwell C, Stuart S, Thompson D, Trillmich F. Global threats to pinnipeds. Mar Mammal Sci. 2012;28(2):414–436.
5. Mercuri M. Varamiento de Mamíferos Marinos en Isla Magdalena, B.C.S., México y su Relación con Factores Físicos y Biológicos. [dissertation]. La Paz BCS, Instituto Politecnico Nacional, Centro Interdisciplinario de Ciencias Marinas. 2007.