Editing Surf scoter (section)

=== Threats ===
In a [[necrotic]] study on sea ducks, parasitic diseases were an important cause of mortality. The only parasite found in dead surf scoters was the Acanthocephalan ''Polymorphus'' spp., which causes [[peritonitis]], an inflammation of the abdomen's lining, and possibly [[emaciation]]. Out of 39 studied individuals, seven were fatally affected by this worm. A mortality of about 100 surf scoters was also estimated along the coast of California in the spring of 1995. The other mortality causes included emaciation due to starvation (17 individuals), toxicity from petroleum (3 individuals), and trauma from firearm or collisions in different structures (2 individuals).<ref>{{cite journal|last1=Skerratt|first1=Lee F.|last2=Franson|first2=J. Christian|last3=Meteyer|first3=Carol U.|last4=Hollmén|first4=Tuula E.|title=Causes of mortality in sea ducks (Mergini) necropsied at the USGS-National wildlife health center|journal=Waterbirds|date=2005|volume=28|issue=2|pages=193–207|jstor=4132527|doi=10.1675/1524-4695(2005)028[0193:comisd]2.0.co;2|s2cid=86513784 }}</ref>

Predation of eggs and ducklings have not been studied in detail but bald eagles, golden eagles and mustelids have been identified as the main predators of surf scoters in marine habitats. Marked individuals showed a higher mortality rate in winter than during wing molt.<ref>{{cite journal|last1=Anderson|first1=Eric M.|last2=Esler|first2=Daniel|last3=Boyd|first3=W. Sean|last4=Evenson|first4=Joseph R.|last5=Nysewander|first5=David R.|last6=Ward|first6=David H.|last7=Dickson|first7=Ryan D.|last8=Uher-Koch|first8=Brian D.|last9=VanStratt|first9=Corey S.|last10=Hupp|first10=Jerry W.|title=Predation rates, timing, and predator composition for Scoters (''Melanitta'' spp.) in marine habitats|journal=Canadian Journal of Zoology|date=2012|volume=90|issue=1 |pages=42–50|doi=10.1139/Z11-110|bibcode=2012CaJZ...90...42A |s2cid=32915468}}</ref>

In November, 2007, an oil spill in San Francisco harbour oiled and killed thousands of birds including many surf scoters. About 40% of the birds affected were from this species. Scientists said that while the species is not endangered it has declined 50 to 70% over the past 40 years and this spill could decrease populations since most of the affected birds are healthy adults.<ref>San Fran oil spill hurts Canadian sea duck population. CBC News. November 23, 2007. [https://www.cbc.ca/news/science/san-fran-oil-spill-hurts-canadian-sea-duck-population-1.654444]</ref>