Pcf. Shepherd et Js. Boates, Effects of a commercial baitworm harvest on semipalmated sandpipers and their prey in the bay of fundy hemispheric shorebird reserve, CONSER BIOL, 13(2), 1999, pp. 347-356
The conservation of key stopover sites for migratory wading birds in import
ant because there are so few and because in some cases they support entire
populations. In Minas Basin in the Bay of Fundy, over 500,000 Semipalmated
Sandpipers (Calidris pusilla) on southward migration feed on the abundant a
mphipod Corophium volutator. When a baitworm harvesting industry began ther
e in 1985 (focused on bloodworms [Glycera dibranchiata]), concerns were rai
sed about the potential effects of this activity on the foraging behavior o
f semipalmated Sandpipers and on the density and age structure of their pri
ncipal prey, C. volutator. Core sampling for invertebrates and paired focal
sandpiper observations were undertaken in disturbed (dug) and undisturbed
sediment. Semipalmated Sandpiper foraging efficiency decreased by 68.5% in
dug sediment, corresponding to observed reductions in prey density. The dec
reased foraging efficiency may also have been related to reductions in prey
availability due to the obstruction of visual and tactile prey cues caused
by turning and loosening of the surface sediment. The overall density (adu
lt and juvenile) of C. volutator decreased by 38.8% in dug sediment in the
first year of baitworm harvesting, due to direct mortality and lower juveni
le recruitment. Juvenile C. volutator were particularly susceptible to dist
urbance (55% decrease in dug sediment); because they overwinter to become t
he next year's potential breeders, this decrease can be expected to compoun
d with each subsequent year of harvesting. All the significant, negative ef
fects of baitworm harvesting on Semipalmated Sandpiper foraging behavior an
d on the density and age structure of their principal prey, C. volutator, w
ere realized after only one season of digging. Semipalmated Sandpipers fora
ging in harvested areas may take longer to deposit the fat required for mig
ration, thereby delaying their arrival on the wintering grounds or forcing
them to depart without sufficient fat loads.