CAUSES OF MORTALITY IN NORTHERN FUR SEALS (CALLORHINUS URSINUS), ST. PAUL ISLAND, PRIBILOF ISLANDS, ALASKA, 1986–2006

To determine whether infectious diseases might have contributed to the present-day decline of northern fur seals (Callorhinus ursinus), preweaned pups (n=2,735), subadult males (n=98), and adults (n=179) were examined postmortem from 1986 to 2006 on St. Paul Island, Alaska. Gross necropsy findings and histologic lesions were used to determine causes of death. Five general categories of mortality were identified for pups: emaciation (1,454 pups, 53%), trauma (497 pups, 18%), perinatal mortality (516 pups, 19%), infectious diseases (82 pups, 3%), and miscellaneous causes (186 pups, 7%). A condition of unknown etiology characterized by multifocal necrotizing myopathy and cardiomyopathy was found in 92 pups. Thirty-three congenital anomalies were identified in 49 pups, including a rare multicentric ganglioneuro-blastoma. General linear models were used to examine change in pup mortality and condition (i.e., pup mass) over time. The prevalence of perinatal mortality appeared to increase during the study and relative to past reports. Trauma and infectious conditions appeared to decrease slightly from 1986 to 2006. Although relatively stable during this investigation, emaciation was greater than that reported for past studies. Emaciated pups weighed less than expected during 1988, 1996, and 2004 and more than expected during 1987, 1989, 1990, and 1994 (P≤0.003). Average annual weights for all other categories of mortality did not change significantly from 1986 to 2006. Fatal conditions for subadult males included hyperthermia, blunt trauma, entanglement, and bite wounds; nonfatal conditions included seizures, orange discoloration of the blubber, neoplasia, and parasitism. Causes of mortality for most adults included bite wounds with cellulitis and secondary infections, pulmonary edema, dystocia, blunt trauma, and neoplasia. We found no evidence to implicate infectious diseases as a cause in the recent decline of northern fur seals.

[1]  W. Gilmartin,et al.  SURVEY OF DISEASES IN FREE-LIVING CALIFORNIA SEA LIONS , 1974, Journal of wildlife diseases.

[2]  F. Gulland,et al.  CONGENITAL DEFECTS IN NORTHERN ELEPHANT SEALS STRANDED ALONG THE CENTRAL CALIFORNIA COAST , 1997, Journal of wildlife diseases.

[3]  R. J. Brown,et al.  RENAL FIBROSARCOMA IN THE NORTHERN FUR SEAL , 1975, Journal of wildlife diseases.

[4]  T. Collier,et al.  Mass spectrometric analysis for aromatic compounds in bile of fish sampled after the Exxon Valdez oil spill , 1992 .

[5]  O. Olsen.  Hookworms, Uncinaria lucasi Stiles, 1901, in fur seals, Callorhinus ursinus (Linn.), on the Pribilof Islands. , 1958 .

[6]  D. Forrester,et al.  Dipetalonema odendhali (Nematoda: Filarioidea) from the northern fur seal, with a description of the microfilaria. , 1971, The Journal of parasitology.

[7]  M. Dailey.  Parasitology - basic considerations , 1986 .

[8]  G. Migaki,et al.  Some histopathological lesions caused by helminths in marine mammals. , 1971, Journal of wildlife diseases.

[9]  A. York,et al.  Pup Production Following Harvest of Female Northern Fur Seals , 1981 .

[10]  U. Siebert,et al.  Parapoxvirus Infection in Harbor Seals (Phoca vitulina) from the German North Sea , 2003, Veterinary pathology.

[11]  T. Williams,et al.  Sequential megafaunal collapse in the North Pacific Ocean: An ongoing legacy of industrial whaling? , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[12]  M. Hindell,et al.  Comparison of southern elephant seal populations, and observations of a population on a demographic knife-edge , 2005 .

[13]  E. Lyons,et al.  HOOKWORM ENTERITIS WITH BACTEREMIA IN CALIFORNIA SEA LION PUPS ON SAN MIGUEL ISLAND , 2007, Journal of wildlife diseases.

[14]  Roman Marin,et al.  Mortality of sea lions along the central California coast linked to a toxic diatom bloom , 2000, Nature.

[15]  G. Migaki,et al.  SOME HISTOPATHOLOGICAL LESIONS CAUSED BY HELMINTHS IN MARINE MAMMALS1 , 1971, Wildlife disease.

[16]  Johnston Dg,et al.  Parasitism in some marine mammals. , 1969 .

[17]  H. Baylis.  On the ascarids parasitic in seals, with special reference to the genus Contracaecum , 1937, Parasitology.

[18]  R. Towell,et al.  DECLINE IN NORTHERN FUR SEAL (CALLORHINUS URSINUS) PUP PRODUCTION ON THE PRIBILOF ISLANDS , 2006 .

[19]  S. T. Zimmerman,et al.  The 1985 Subsistence Harvest of Northern Fur Seals, Callorhinus ursinus, on St. Paul Island, Alaska , 1985 .

[20]  E. Lyons.  Biology of the hookworm, Uncinaria lucasi Stiles, 1901, in the northern fur seal, Cattorhinus ursinus Linn, on the Pribilof Islands, Alaska. , 1964 .

[21]  R. Condit,et al.  PATHOLOGY AND PRELIMINARY CHARACTERIZATION OF A PARAPOXVIRUS ISOLATED FROM A CALIFORNIA SEA LION (ZALOPHUS CALIFORNIANUS) , 2006, Journal of wildlife diseases.

[22]  T. Hulland.  CHAPTER 2 – Muscle and Tendon , 1993 .

[23]  K. Beckmen,et al.  INFECTIOUS DISEASE AND THE DECLINE OF STELLER SEA LIONS (EUMETOPIAS JUBATUS) IN ALASKA, USA: INSIGHTS FROM SEROLOGIC DATA , 2005, Journal of wildlife diseases.

[24]  Thomas R. Loughlin,et al.  Separation of foraging habitat among breeding sites of a colonial marine predator, the northern fur seal (Callorhinus ursinus) , 2004 .

[25]  Dickson D. Despommier,et al.  Parasitic Diseases , 1989, Springer US.

[26]  M. Marsh.  THE FUR SEAL MORTALITY OF THE PRIBILOF ROOKERIES IN THE ABSENCE OF PELAGIC SEALING. , 1912, Science.

[27]  C. Schroeder,et al.  The occurrence of gastric ulcers in sea mammals of the California coast, their etiology and pathology. , 1935 .

[28]  L. Brain.  The Nervous System , 1963, Nature.

[29]  M. Zamorani,et al.  Muscle and Tendon , 2007 .

[30]  I. Boyd,et al.  Aging live Antarctic fur seals and southern elephant seals , 1992 .

[31]  R. Ream,et al.  At-sea behavior of juvenile male northern fur seals (Callorhinus ursinus) , 2004 .

[32]  S. Hayama,et al.  A Case of Cleft Palate in a Kuril Seal (Phoca vitulina stejnegeri), from Hokkaido, Japan , 1992, Journal of Wildlife Diseases.

[33]  E. Lyons,et al.  Ascaridoid Nematodes and Associated Lesions in Stomachs of Subadult Male Northern Fur Seals (Callorhinus Ursinus) on St. Paul Island, Alaska: (1987—1999) , 2003, Journal of veterinary diagnostic investigation : official publication of the American Association of Veterinary Laboratory Diagnosticians, Inc.

[34]  R. Gentry,et al.  Chapter 3. Attendance Behavior of Northern Fur Seals , 1986 .

[35]  A. York,et al.  Using Age Structure to Detect Impacts on Threatened Populations: a Case Study with Steller Sea Lions , 2003 .

[36]  P. A. Larkin,et al.  The Decline and Fall of the Pribilof Fur Seal (Callorhinus ursinus): A Simulation Study , 1989 .

[37]  L. Griner,et al.  Pathology of Zoo Animals , 1983 .

[38]  J. Laake,et al.  Seasonal prevalence and intensity of hookworms (Uncinaria spp.) in California sea lion (Zalophus californianus) pups born in 2002 on San Miguel Island, California , 2005, Parasitology Research.

[39]  Keyes Mc.  Pathology of the northern fur seal. , 1965 .

[40]  J. Testa.  Fur Seal Investigations, 2004-2005 , 2007 .

[41]  M. M. Krahn,et al.  Standard analytical procedures of the NOAA National Analytical Facility, 1986 : metabolites of aromatic compounds in fish bile , 1986 .

[42]  A. Trites,et al.  Changes in body growth of northern fur seals from 1958 to 1974: density effects or changes in the ecosystem? , 1992 .

[43]  J. Baker.  Mortality and morbidity in grey seal pups (Halichoerus grypus). Studies on its causes, effects of environment, the nature and sources of infectious agents and the immunological status of pups , 2009 .