Getting to the Arctic on time: Horseshoe Crabs and Knot in Delaware Bay

Arctic breeding waders are often constrained by the availability of resources at stop over sites on their northward migration to the breeding grounds. These constraints become most acute at their last stopover before they reach the breeding grounds as late arrival, or arrival in poor condition, may lead to a reduction in breeding productivity and subsequent survival.

The situation in Delaware Bay, USA is particularly difficult for migrating waders, as they depend largely on the eggs of Horseshoe Crabs that are exposed on the beach surface. These surface eggs are abundant only when there are extremely large numbers of breeding crabs. In the early 1990’s there was a dramatic increase in the Horseshoe Crab fishery which lead to a major reduction in spawning crab numbers. This resulted in a reduction in the rate of weight gain of migrating waders, particularly Knot, and coincided with a dramatic decline in the population. Initial responses of the conservation community were to call for a permanent ban on Horseshoe Crab fishing which lead to the imposition of harvest quotas, and in some States a complete moratorium. The first signs of a recovery in the Horseshoe Crab population are beginning to appear, which has in turn lead to the call from fishing interests for increases in fishing quotas. The conservation community had been collecting extensive ecological data over a decade which proved the link between food supplies and the condition of the birds but this is not easy to explain to non-scientists. The way forward was found after many days of discussions between all parties. The result is an Adaptive Resource Management approach and gives hope for the future of the Horseshoe Crabs and Knot.

Nigel Clark, BTO, Thetford