Effects of a commercial baitworm harvest on semipalmated sandpipers and their prey in the bay of fundy hemispheric shorebird reserve

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.