Second North American Sea Duck Conference - Patuxent Wildlife ...

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
POPULATION TRENDS AND COLONY DYNAMICS
OF COMMON EIDERS
Gregory J. Robertson, Keith G. Chaulk, William A. Montevecchi, Brian T. Collins, and Bruce C.
Turner
GJR and BCT: Canadian Wildlife Service, 6 Bruce Street, Mount Pearl, NL, A1N 4T3; KGC:
Labrador Inuit Association, Goose Bay, NL, A0P 1C0; WAM: Department of Psychology, Memorial
University of Newfoundland, St. John’s, NL, A1B 3X9;
BTC: Canadian Wildlife Service, National Wildlife Research Centre, Raven Road, Carleton
University, Ottawa, ON, K1A 0H3; greg.robertson@ec.gc.ca
Common eiders (Somateria mollissima) breeding in many northern areas are experiencing population
declines. Although coastal Labrador harbors important concentrations of breeding common eiders
and includes the zone of intergradation between the dresseri and borealis subspecies, there has been
relatively little work done on these populations. From 1998 to 2003, ground surveys were conducted
on the Labrador coast (52º - 57º N), where 117 islands were surveyed a total of 479 times in four
archipelagos (Nain, Hopedale, Rigolet, St. Peter’s Bay) and 13,185 nests were counted. Using the
population trend software (ESTEQNINDEX) to estimate annual increases in nesting eiders over
this six-year period, substantial annual increases with an overall average annual growth of 17.5%
were found. Definitive reasons to explain these increases are not known, but may be related to an
amelioration of environmental conditions and management strategies that have reduced late season
bags in Newfoundland. In addition, the closure of Atlantic salmon (Salmo salar) and cod (Gadidae)
fisheries has resulted in significant decreases in human activity in Labrador; which likely reduced
bycatch in fishing gear, summer hunting, and disturbance. To further understand how common eiders
were distributed spatially and temporally across islands, a metapopulation approach was used to
examine colony dynamics. Smaller colonies were more prone to extinction, but colonization was not
related to island isolation. Mean abundance was a positive predictor of incidence, in other words, in
areas of with larger colonies, more local islands were occupied. The overall extinction rate was 0.08
± 0.01 (SE) and colonization rate was 0.12 ± 0.02 suggesting considerable turnover in eider colonies,
but these rates showed substantial variation within and across archipelagos. Eiders colony locations
in northern areas are transient and their persistence is related to their size, and the presence and size
of adjacent colonies. Combined, this information should aid managers in setting sustainable harvest
levels and appropriate land use policies that are conducive to eiders breeding in Labrador.
110 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005