Overall, 489 aggregations (including singles) containing 14,638 long-tailed ducks and surf scoters were observed during this study. Just over 12,000 and 2,600 were found in the Chesapeake Bay and Hog Island Bay study areas, respectively.
Surf scoters were the dominant species accounting for 13,685 (93%) of sea ducks counted during surveys in 317 aggregations.
Long-tailed ducks in 172 aggregations accounted for 953 (7%) of the ducks counted.
Surf scoters arrived in both study areas well before long-tailed ducks.
Both species scattered throughout Chesapeake Bay, but larger groups were well offshore (Fig. 3).
Long-tailed ducks tended to be scattered throughout Hog Island Bay, but surf scoters were concentrated in a relatively narrow band along a shoal area just west of High Shoal Marsh.
Long-tailed ducks aggregation size was significantly smaller than that of surf scoters.
Habitat Characteristics
No significant difference in mean foraging depths between long-tailed ducks and surf scoters, though long-tailed ducks did tend to be found in slightly deeper water than surf scoters on average in CB.
The percentage of organic matter was significantly higher in long-tailed duck foraging areas than those of surf scoters in Hog Island Bay, but not in Chesapeake Bay.
Chesapeake Bay foraging areas were dominated by medium/coarse sand (56%) and fine/very fine sand (43%), whereas Hog Island Bay tended towards higher fine/very fine sand (77%) and silt/clay (22%) fractions. Minor differences between species-specific foraging areas were noted within each study area.
Organisms in 22 broad taxa were identified from sea duck foraging areas (146 species/taxa).
Mean total biomass of benthic organisms was higher in Hog Island Bay than Chesapeake Bay and higher in long-tailed ducks foraging areas in Hog Island Bay compared to those of surf scoters.
Amphipods, bivalves, gastropods and polychaetes were generally the dominant broad taxa in terms of biomass, although brachyurans, echinoderms, and nemerteans were also important in Hog Island Bay foraging areas.
Overall, 15% of long-tailed duck aggregations and 18% of surf scoters aggregations were within 730 meters of emergent shoreline.
Less than 1% of aggregations were within 50 meters of SAV patches and none were overlapping them.
Within Hog Island Bay, 1% of long-tailed duck aggregations and 9% of surf scoter aggregations were within 50 m of reefs while 2% and 6% of each species aggregations, respectively, overlapped them.
Diet
60 long-tailed ducks and 44 surf scoters were haphazardly collected (Figs. 5 and 6).
Two surf scoters collected in January 2009 from the Chesapeake Bay study area were banded in Labrador, Canada; one in 2004 and one in 2007 (Fig. 7).
Anatomical measurements for all parameters were lower for long-tailed ducks than surf scoters.
Of the 60 long-tailed ducks collected, 55 (92%) had esophageal contents and 59 (98%) had gizzard contents. All 60 (100%) had prey in either their esophagus or gizzard. However, of the 44 surf scoters collected, only 26 (59%) and 40 (91%) had esophageal or gizzard contents, respectively. Overall, 40 (91%) had prey in either their esophagus or gizzard.
Long-tailed ducks esophagi and gizzards had significantly higher total abundance and biomass of prey items than those of surf scoters across both study areas.
Organisms in 23 broad taxa were identified from sea duck esophagi/gizzards (96 species/taxa). Ascidians, bivalves, brachyurans, gastropods and polychaetes were found in esophagi and/or gizzards of both duck species in both study areas
Ascidians, mainly Molgula, and amphipods were found in high relative abundance in long-tailed duck esophagi in Chesapeake Bay and Hog Island Bay, respectively, while their dominance diminished when measured by dry tissue biomass relative to taxa such as polychaetes and bivalves, and especially for amphipods.
Surf scoters esophagi were dominated by bivalves in both study areas and, additionally, polychaetes and nemerteans in Chesapeake Bay.
The suite of genera dominating bivalves, gastropods and polychaetes was slightly different between study areas and duck species.
Long-tailed ducks had many more unique broad taxa than surf scoters and these were not rare (found in > 10% of samples) in many cases.
Mean taxa richness was higher for long-tailed ducks than surf scoters, but the mean Shannon Index, was similar between the two species.
