Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The global population is estimated to number c.250,000-1,300,000 individuals (Wetlands International 2006), while the population in Russia has been estimated at <100 breeding pairs (Brazil 2009).
The overall population trend is decreasing, although some populations have unknown trends (Wetlands International 2006). This species has undergone a small or statistically insignificant decrease over the last 40 years in North America (data from Breeding Bird Survey/Christmas Bird Count: Butcher and Niven 2007) Note, however, that these surveys cover less than 50% of the species's range in North America.
The Surf Scoter can be found in North America, breeding inland from western Alaska (USA) through central Canada to Labrador, and wintering from the Aleutian Islands down to Baja California (Mexico) on the Pacific coast, and along the Atlantic coast of the USA as far south as South Carolina (del Hoyo et al. 1996) .
This species breeds on small bodies of fresh water in boreal forests or tundra, wintering at sea in shallow waters of bays, estuaries and river mouths. It feeds chiefly on molluscs, but also eats crustaceans, worms, echinoderms and, mainly in summer; insects and their larvae and plant material, feeding mostly by diving. Its breeding season begins in May or June, when it breeds in single pairs or loose groups in shallow depressions poorly lined with grass and some feathers (del Hoyo et al. 1996) .
Hunting poses a major threat to this species, with an estimated harvest of 18,000 to 45,000 individuals taken in the 10-year period from 2004-2014 in the US and Canada, but with a downward trend (Canadian Wildlife Service Waterfowl Committee 2015). A recent estimate suggests that the harvest of Surf Scoters may be 22-37% over the maximum sustainable rate for the east coast and 60-66% for the west coast (Koneff et al. 2017).
Climate change is affecting the species through habitat loss and causing trophic mismatch. Decreasing snow cover duration during spring in boreal regions has been linked to population declines of Scoters, likely due to trophic mismatch, with a projected 31.0% decline in the population by 2080 compared to 1980 (Drever et al. 2011). Ocean acidification may lead to declines in molluscs which form a large part of the Surf Scoter diet (Steinacher et al. 2009; Carboneras and Kirwan 2017). Wetlands provide important breeding grounds for this species, but are now at risk of loss or degradation; remote sensing and imaging has shown shrinkage and disappearance of lakes and ponds in Alaska and Siberia (Smith et al. 2005, Riordan et al. 2006). In general, climate change is predicted to cause dramatic habitat changes in the Arctic region (Fox et al. 2015).
The species is one of the most vulnerable seabirds to oil pollution (Anderson et al. 2015) and was one of the most severely affected species in the 2007 Cosco Busan oil spill in San Francisco Bay with an estimated mortality of 4% (Ford et al. 2009). Pollution from oil and gas exploration is a pervasive threat in the Arctic which is likely to increase in the future (Poland et al. 2003, Henderson and Loe 2014). Sea ducks in the Pacific Northwest could be exposed to toxicologically significant levels of cadmium associated with mussels foraged from aquaculture structures, which raises the possibility that such exposure could be contributing to observed population declines (Bendell 2011).Although surveys have found dead individuals of this species in recovered derelict fishing gear in Salient Sea, Washington (Good et al. 2009), bycatch does not appear to be a major source of mortality in other regions (Hamel et al. 2009).
Text account compilers
Calvert, R., Arendarczyk, B., Ekstrom, J., Butchart, S., Fjagesund, T., Hermes, C., Palmer-Newton, A., Stuart, A.
BirdLife International (2019) Species factsheet: Melanitta perspicillata. Downloaded from http://www.birdlife.org on 19/10/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/10/2019.