Volume 51, No. 1

Search by author or title:

Demographics and gross pathology of scoters and scaups killed by the Cosco Busan oil spill in California


1Oikonos Ecosystem Knowledge, P.O. Box 2570, Santa Cruz, California 95063, USA *(
2California Department of Fish and Wildlife, Office of Spill Prevention and Response, Marine Wildlife Veterinary Care and Research Center, 1451 Shaffer Rd, Santa Cruz, California 95060, USA
3Wildlife Health Center, School of Veterinary Medicine, University of California, One Shields Ave., Davis, California 95616, USA
4U.S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, PO Box 158, Moffett Field, California 94035-0158, USA


BECK, J. CARLE, R.D., NEVINS, H., DE LA CRUZ, S.E.W. & DONNELLY-GREENAN, E. 2023. Demographics and gross pathology of scoters and scaups killed by the Cosco Busan oil spill in California. Marine Ornithology 51: 69 - 78

Received 11 July 2022; accepted 22 December 2022

Date Published: 2023/04/15
Date Online: 2023/04/10
Key words: Melanitta, Aythya, sea duck, acanthocephalan, mycotic disease, parasite, sex ratio


Unusual wildlife mortality events provide a unique opportunity to collect information on demographics, disease, and body condition in affected wildlife, which may be useful for informing oil spill damage assessments and future spill responses. In November 2007, the Cosco Busan Oil Spill occurred in San Francisco Bay, California, a globally important wintering area for waterfowl. The spill resulted in the mortality of scoters Melanitta spp. and scaups Aythya spp., species that have declined significantly over recent decades. We examined the demography (sex and age ratios) and prevalence of grossly apparent disease (acanthocephalan parasite infection and mycotic disease) in 288 Surf Scoters M. perspicillata, White-winged Scoters M. deglandi, Greater Scaup A. marila, and Lesser Scaup A. affinis killed in the oil spill. The proportions of females and juveniles in examined Surf Scoters was unexpectedly high (0.98:1, females:males, 0.73:1 juveniles:adults) for this species with normally strong male- and adult-biased populations. This disproportionate mortality of female Surf Scoters could result in a greater population impact on this female-limited species, suggesting a mechanism for steep declines in San Francisco Bay scoter numbers in the years after the Cosco Busan oil spill. Significantly greater rates of acanthocephalan infection in juvenile vs. adult Surf Scoters indicated a possible interaction between acanthocephalan parasitism and juvenile-biased mortality in our sample. Birds that died during rehabilitation had significantly greater rates of mycotic disease (10% infected) than birds found dead in the field (3%), indicating that infections began or worsened during rehabilitation. Greater Scaup had proportionally greater rates of infection with mycotic disease (26% of individuals) than other species, indicating that they may be particularly susceptible to the disease. We encourage the documentation of demographics and disease as a regular part of future responses to oil spills, or other mortality events, to gain insight into population impacts and improve rehabilitation efforts of affected populations.


ACCURSO, L.M. 1992. Distribution and abundance of wintering waterfowl on San Francisco Bay, 1988-1990. MSc Thesis. Arcata, USA: Humboldt State University.

AFTON, A.D. & ANDERSON, M.G. 2001. Declining scaup populations: a retrospective analysis of long-term population and harvest survey data. Journal of Wildlife Management 65: 781-796. doi:10.2307/3803028

ALEXANDER, W.C. 1983. Differential sex distributions of wintering diving ducks (Aythyini) in North America. American Birds 37: 26-29.

ANDERSON, B.W., KETOLA, T.E. & WARNER, D.W. 1969. Spring sex and age ratios of lesser scaup and ring-necked ducks in Minnesota. Journal of Wildlife Management 33: 209-212.

ANDERSON, E.M., DICKSON, R.D., LOK, E.K. ET AL. 2020. Surf Scoter (Melanitta perspicillata), version 1.0. In: Rodewald, P.G. (Ed.) Birds of the World. Ithaca, USA: Cornell Lab of Ornithology. [Accessed at on 26 July 2020.] doi:10.2173/bow.sursco.01

ANKER-NILSSEN, T., JONES P.H. & RØSTAD O.W. 1988. Age, sex, and origins of auks (Alcidae) killed in Skagerrak oiling incident of January 1981. Seabird 11: 28-46.

ARNÉ, P., RISCO-CASTILLO, V., JOUVION, G., LE BARZIC, C. & GUILLOT, J. 2021. Aspergillosis in wild birds. Journal of Fungi 7: 241. doi:10.3390/jof7030241

ASAKURA, S., NAKAGAWA, S., MASUI, M. & YASUDA, J. 1962. Immunological studies of aspergillosis in birds. Mycopathologia et Mycologia Applicate 4: 249-256.

AUSTIN, J.E., AFTON, A.D. & ANDERSON, M.G. ET AL. 2000. Declining scaup populations: Issues, hypotheses, and research needs. Wildlife Society Bulletin 28: 254-263.

BALSEIRO, A., ESPI, A., MARQUEZ, I., PEREZ, V., FERRERAS, M. C., MARIN, J. G., & PRIETO, J. M. 2005. Pathological features in marine birds affected by the Prestige's oil spill in the north of Spain. Journal of Wildlife Diseases 2: 371-378.

BEERNAERT, L.A., PASMANS, F., VAN WAEYENBERGHE, L., HAESEBROUCK F. & MARTEL A. 2010. Aspergillus infections in birds: a review. Avian Pathology 39: 325-331. doi:10.1080/03079457.2010.506210

BOWMAN, T.D., SILVERMAN, E.D., GILLILAND, S.G. & LERINESS, J.B. 2015. Status and trends of North American Sea Ducks: reinforcing the need for better monitoring. In: SAVARD, J.-P.L., DERKSEN, D.V., ESLER D. & EADIE, J.M. (Eds.) Ecology and Conservation of North American Sea Ducks. Studies in Avian Biology 46. Boca Raton, USA: CRC Press.

BOURGEOIS, C. E. & THRELFALL, W. 1982. Metazoan parasites of three species of scoter (Anatidae). Canadian Journal of Zoology 60: 2253-2257.

BRIGGS, K.T., TYLER, B.W., LEWIS, D.B. & CARLSON, D.R. 1987. Bird communities at sea off California 1975 to 1983. Studies in Avian Biology 11:1-74.

BRIGGS K.T., YOSHIDA S.H. & GERSHWIN M.E. 1997. The influence of petrochemicals and stress on the immune system of seabirds. Regulatory Toxicology and Pharmacology 97: 194.

BROUGHTON, J. M. 1994. Size of the bursa of Fabricius in relation to gonad size and age in Laysan and Black-footed albatrosses. The Condor 96: 203-207.

BURCO, J.D., ETIENNE, E.A., MASSEY, J.G., ZICCARDI, M.H. & BALAJEE, S.A. 2012. Molecular sub-typing suggests that the environment of rehabilitation centers may be a potential source of Aspergillus fumigatus infecting rehabilitating seabirds. Medical Mycology 50: 91-98. doi:10.3109/13693786.2011.592860

BURCO, J.D., MASSEY, J.G., BYRNE, B.A., TELL, L., CLEMONS, K.V. & ZICCARDI, M.H. 2014. Monitoring of fungal loads in seabird rehabilitation centers with comparisons to natural seabird environments in northern California. Journal of Zoo and Wildlife Medicine 45: 29-40.

BURGHERR, P. 2007. In-depth analysis of accidental oil spills from tankers in the context of global spill trends from all sources. Journal of Hazardous Materials 140: 245-256.

BUSH, A.O. & HOLMES, J.C. 1986. Intestinal helminths of lesser scaup ducks: an interactive community. Canadian Journal of Zoology 64: 142-152.

CAMPHUYSEN, C.J., BERREVOETS, C.M., CREMERS, H.J.W.M. ET AL. 2002. Mass mortality of common eiders (Somateria mollissima) in the Dutch Wadden Sea, winter 1999/2000: Starvation in a commercially exploited wetland of international importance. Biological Conservation 106: 303-317. doi:10.1016/S0006-3207(01)00256-7

CARTER, H.R. & KULETZ, K.J. 1995. Mortality of Marbled Murrelets due to oil pollution in North America. In: RALPH, C.J, HUNT JR., G.L., RAPHAEL, M.G. & PIATT, J.F. (Eds.) Ecology and conservation of the Marbled Murrelet. Gen. Tech. Rep. PSW-GTR-152. Albany, USA: Pacific Southwest Research Station, Forest Service, US Department of Agriculture.

CHING, H.L. 1989. Profilicollis botulus (Van Cleave, 1916) from diving ducks and shore crabs of British Columbia. The Journal of Parasitology 75: 33-37.

COLE, R.A. 1999. Acanthocephaliasis. In: FRIEND, M. & FRANSON, J.C. (Eds.) Field Manual of Wildlife Diseases: General Field Procedures and Diseases of Birds. Information and Technology Report 1999-001. Madison, USA: USGS Biological Resources Division, National Wildlife Health Center.

Cosco Busan Oil Spill Trustees. 2012. Cosco Busan Oil Spill Final Damage Assessment and Restoration Plan/Environmental Assessment. California Department of Fish and Game, California State Lands Commission, National Oceanic and Atmospheric Administration, United States Fish and Wildlife Service, National Park Service, Bureau of Land Management.

DE LA CRUZ S.E.W., EADIE J.M., MILES A.K. ET AL. 2014. Resource selection and space use by sea ducks during the non-breeding season: implications for habitat conservation planning in urbanized estuaries. Biological Conservation 169: 68-78. doi:10.1016/j.biocon.2013.10.021

EAGLES-SMITH, C.A., ACKERMAN, J.T., DE LA CRUZ, S.E.W. & TAKEKAWA J.Y. 2009. Mercury bioaccumulation and risk to three waterbird foraging guilds is influenced by foraging ecology and breeding stage. Environmental Pollution 157: 1993-2002. doi:10.1016/j.envpol.2009.03.030

ENGLAND, J.C., LEVENGOOD, J.M., OSBORN, J.M. ET AL. 2016. Spatiotemporal distributions of intestinal helminths in female lesser scaup Aythya affinis during spring migration from the upper Midwest, USA. Journal of Helminthology 1-12. doi:10.1017/S0022149X16000493

FLINT, P.L. 2015. Population dynamics of sea ducks. In: SAVARD, J.-P.L., DERKSON, D.V., ESLER, D. & EADIE, J.M. (Eds.) Ecology and Conservation of North American Sea Ducks. Studies in Avian Biology 46. Boca Raton, USA: CRC Press.

FORD, R.G., CASEY, J.L. & WILLIAMS, W.A. 2009. Final report: Acute seabird and waterfowl mortality resulting from the M/V Cosco Busan oil spill, November 7, 2007. Report to the California Department of Fish and Game Office of Oil Spill Prevention and Response. Portland, USA: R.G. Ford Consulting Company.

Franeker, J.V. 2004. Save the North Sea - Fulmar Study Manual 1: Collection and dissection procedures. Alterra-Rapport 401. Wageningen, Netherlands: Alterra Institute, Wageningen University and Research Centre.

HANEY, J.C., GEIGER, H.J. & SHORT, J.W. 2014. Bird mortality from the Deepwater Horizon oil spill. II. Carcass sampling and exposure probability in the coastal Gulf of Mexico. Marine Ecology Progress Series 513: 239-252. doi:10.3354/meps10839

HAMILTON, L.J., MICHEL, N.L, EVENSON, J.R. & ROBERTS, D.L. 2022. Surf scoters use deeper offshore waters during nocturnal resting periods in the Salish Sea of Washington and British Columbia. Ornithological Applications 124: 1-12.

HAMPTON S., FORD, R.G., CARTER, H.R., ABRAHAM, C. & HUMPLE, D. 2003. Chronic oiling and seabird mortality from the sunken vessel S.S. Jacob Luckenbach in Central California. Marine Ornithology 31: 35-41.

HARIO, M., LEHTONEN, J.T. & HOLLMÉN, T. 1995. Väkäkärsämodot haahkan kuolevuustekijänä—epäilevä näkokanta. Suomen Riista 41: 21-26.

HENNESSY, S.L. & MOREJOHN, G.V. 1977. Acanthocephalan parasites of the sea otter, Enhydra lutris, off coastal California. California Department of Fish and Game 63: 268-272.

HILLGARTH, N. & KEAR, J. 1979. Diseases of seaducks in captivity. Wildfowl 30: 135-141.

HOLLMÉN, T.E. & FRANSON, J.C. 2015. Infectious diseases, parasites, and biological toxins in sea ducks. In: SAVARD, J.-P.L., DERKSEN, D.V., ESLER D. & EADIE, J.M. (Eds.) Ecology and Conservation of North American Sea Ducks. Studies in Avian Biology 46. Boca Raton, USA: CRC Press.

HOROWITZ, D. B. & HAEBLER, R. 2001. Demonstration of Aspergillus sp. in tissues of the Common Loon, Gavier immer: incidence, progression, and severity. Journal of Histotechnology 2: 101-106.

HUMPLE, D. L., NEVINS, H.M., PHILLIPS, E.M. ET AL. 2011. Demographics of Aechmophorus grebes killed in three mortality events in California. Marine Ornithology 39: 235-242.

IVERSON, S.A., ESLER, D. & BOYD W.S. 2003. Plumage characteristics as an indicator of age class in the Surf Scoter. Waterbirds 26: 56-61. doi:10.1675/1524-4695(2003)026[0056:PCAAIO]2.0.CO;2

IVERSON, S.A., SMITH, B.D. & COOKE, F. 2004. Age and sex distributions of wintering Surf Scoters: Implications for the use of age ratios as an index of recruitment. The Condor 106: 252-262. doi:10.1093/condor/106.2.252

KEEVIL, M.G., BROOKS, R.J. & LITZGUS, J.D. 2018. Post‐catastrophe patterns of abundance and survival reveal no evidence of population recovery in a long‐lived animal. Ecosphere 9: e02396.

KING, J.G. & SANGER, G.A. 1979. Oil vulnerability index for marine oriented birds. Conservation of Marine Birds of Northern North America 11: 227-239.

MARTÍNEZ-ABRAÍN, A., VELANDO, A., ORO, D. ET AL. 2006. Sex-specific mortality of European shags after the Prestige oil spill: Demographic implications for the recovery of colonies. Marine Ecology Progress Series 318: 271-276. doi:10.3354/meps318271

MASON, J.W., MCCHESNEY, G.J., MCIVER, W.R. ET AL. 2007. At-sea distribution and abundance of seabirds off Southern California: a 20-year comparison. Studies in Avian Biology 33. Camarillo, USA: Cooper Ornithological Society.

MAYER, K., DAILEY, M. & MILLER, M.A. 2003. Helminth parasites of the southern sea otter (Enhydra lutris nereis) from central California: abundance, distribution and pathology. Diseases of Aquatic Organisms 53: 77-82. doi:10.3354/dao053077

MAZET, J.A.K., NEWMAN, S.H., GILARDI, K.V.K ET AL. 2002. Advances in oiled bird emergency medicine and management. Journal of Avian Medical Surgery 16: 146-149. doi:10.1647/1082-6742(2002)016[0146:aiobem];2

MITCHELL, G.J. 1952. A study of the distribution of some members of the Nyrocinae wintering on the coastal waters of southern British Columbia. PhD Thesis. Vancouver, Canada: University of British Columbia.

NEVINS, H.M. & CARTER, H.R. 2003. Age and sex of Common Murres (Uria aalge) recovered during the 1997-98 Point Reyes Tarball Incidents in central California. Marine Ornithology 31: 51-58.

OHLENDORF, H.M. & FLEMING, W.J. 1988. Birds and environmental contaminants in San Francisco and Chesapeake Bays. Marine Pollution Bulletin 19: 487-495.

OHLENDORF, H.M., MAROIS, K.C., LOWE, R.W., HARVEY, T.E. & KELLY, P.R. 1991. Trace elements and organochlorines in Surf Scoters from San Francisco Bay, 1985. Environmental Monitoring and Assessment 18: 105-122.

PATTON, R.T., GOODENOUGH, K.S., DE LA CRUZ, S.E.W. ET AL. 2017. Mass mortality attributed to Acanthocephaliasis at a Gull-billed Tern (Gelochelidon nilotica) (Laridae: Sterninae) colony in coastal California, USA. Journal of Wildlife Disease 53: 885-890.

PETERSON, M.R & SAVARD, J.-P.L. 2015. Variation in migration strategies of North American sea ducks. In: SAVARD, J.-P.L., DERKSEN, D.V., ESLER D. & EADIE, J.M. (Eds.) Ecology and Conservation of North American Sea Ducks. Studies in Avian Biology 46. Boca Raton, USA: CRC Press.

PIATT, J.F., LENSINK, C.J., BUTLER, W., KENDZIOREK, M. & NYSEWANDER, D.R. 1990. Immediate impact of the 'Exxon Valdez 'oil spill on marine birds. The Auk 107: 387-397.

RAMÍREZ-GAROFALO, J.R. 2020. Occurrence and implications of staging Black Scoters Melanitta americana in a heavily trafficked urban estuary. Marine Ornithology 32: 27-32.

RICHMOND, O.M.W., DULAVA, S., STRONG, C.M. & ALBERTSTON, J.D. 2014. San Francisco Estuary Midwinter Waterfowl Survey: 2012 Survey Results and Trend Analysis (1981-2012). Fremont, USA: US Fish and Wildlife Service, Pacific Southwest Region & National Wildlife Refuge System Inventory and Monitoring Initiative.

RODWAY, M.S., REGEHR, H.M. & COOKE, F. 2003. Sex and age differences in distribution, abundance, and habitat preferences of wintering Harlequin Ducks: implications for conservation and estimating recruitment rates. Canadian Journal of Zoology 81: 492-503. doi:10.1139/z03-025

RODWAY, M.S., REGEHR, H.M., BOYD, W.S. & IVERSON, S.A. 2015. Age and sex ratios of sea ducks wintering in the strait of Georgia, British Columbia: Implications for monitoring. Marine Ornithology 43: 141-150.

SAVARD, J.-P.L., DERKSEN, D.V., ESLER D. & EADIE, J.M. 2015 (Eds.) Ecology and Conservation of North American Sea Ducks. Studies in Avian Biology 46. Boca Raton, USA: CRC Press.

Sea Duck Joint Venture. 2007. Recommendations for Monitoring Distribution, Abundance, and Trends for North American Sea Ducks. Anchorage, Alaska, and Sackville, New Brunswick: U.S. Fish and Wildlife Service and Canadian Wildlife Service.

SKERRATT, L.F., FRANSON, J.C., METEYER, C.U. & HOLLMÉN, T.E. 2005. Causes of Mortality in Sea Ducks (Mergini) necropsied at the USGS-National Wildlife Health Center. Waterbirds 28: 193-207. doi:10.1675/1524-4695(2005)028[0193:COMISD]2.0.CO;2

SMAIL, J., AINLEY, D.G. & STRONG, H. 1972. Notes on birds killed in the 1971 San Francisco Oil Spill. California Birds 3: 25-32.

SMITH, N.F. 2007. Associations between shorebird abundance and parasites in the sand crab, Emerita analoga, along the California coast. The Journal of Parasitology 93: 265-273. doi:10.1645/GE-1002R.1

SPERDUTO, M.B., POWERS, S.P. & DONLAN, M. 2003. Scaling restoration to achieve quantitative enhancement of loon, seaduck, and other seabird populations. Marine Ecology Progress Series 264: 221-232. doi:10.3354/meps264221

STETTER, M.D., MANGOLD, B.J., CALLE, P.P. ET AL. 1994. Aspergillosis in Captive Pacific Eiders (Somateria mollissima). IAAAM Archive.

STRONG, C.M. 2018. San Francisco Estuary Midwinter Waterfowl Survey: 2013-2018 Summary Results. Fremont, USA: US Fish and Wildlife Service, San Francisco Bay National Wildlife Refuge Complex.

TAKEKAWA, J.Y., DE LA CRUZ, S.W., WILSON, M.T. ET AL. 2011. Breeding synchrony, sympatry, and nesting areas of Pacific coast surf scoters (Melanitta perspicillata) in the northern boreal forest. Studies in Avian Biology 41: 41-51.

THIELTGES, D.W., HUSSEL, B. & BAEKGAARD, H. 2006. Endoparasites in common eiders Somateria mollissima from birds killed by an oil spill in the northern Wadden Sea. Journal of Sea Research 55: 301-308. doi:10.1016/j.seares.2005.12.001

TOLF, C., LATORRE-MARGALEF, N., WILLE, M. ET AL. 2013. Individual variation in influenza A virus infection histories and long-term immune responses in mallards. PLoS ONE 8: e61201.

Tseng, F.S. 1999. Considerations in care for birds affected by oil spills. Seminars in Avian and Exotic Pet Medicine 8: 21-31. doi:10.1016/S1055-937X(99)80032-2

USGS (United States Geological Survey). 1999. Field Manual of Wildlife Diseases: General Field Procedures and Diseases of Birds. Madison, USA: US Geological Survey, Department of the Interior.

UHER‐KOCH, B.D., ESLER, D., DICKSON, R.D. ET AL. 2014. Survival of surf scoters and white‐winged scoters during remigial molt. The Journal of Wildlife Management 78: 1189-1196.

VERMEER, K. 1981. Food and populations of surf scoters in British Columbia. Wildfowl 32: 106-116.

WIENS, J.A., FORD, R.G. & HEINEMANN, D. 1984. Information needs and priorities for assessing the sensitivity of marine birds to oil spills. Biological Conservation 28: 21-49. doi:10.1016/0006-3207(84)90092-2

ZAFANTE, M. & HAMPTON, S. 2005. Lost bird-years: quantifying bird injuries in natural resource damage assessments for oil spills. International Oil Spill Conference Proceedings 1: 1019-1023.

Search by author or title:

Browse previous volumes: