According to a U.S. Geological Survey study, ecological links exist between
red knots and horseshoe crab populations
Population health of the red knot, a shorebird species whose population has plummeted over the last 15 years, has been directly tied to the number of egg-laying horseshoe crabs in Delaware Bay during the red knot’s northward migration each spring.
The research appears to support the hypothesis that managing horseshoe crab populations and their harvest may help conserve red knots. Horseshoe crabs are harvested for bait. They are also used in the pharmaceutical industry, which collects their blood for its clotting properties.
The study, which looked at data from more than 16,000 birds over a 12-year period, revealed that the chance of a red knot gaining significant weight after arriving at Delaware Bay is directly related to the estimated number of female horseshoe crabs that spawned during the shorebird stopover period each spring.
Birds that do not gain enough weight tend to have a lower chance of surviving the rest of the year, and in some years the difference between heavy and light bird survival can be large.
The research also found evidence that the annual survival of these birds is not only partly dependent on their body mass when they leave Delaware Bay but is also strongly related to snow conditions when the birds reach their arctic breeding grounds.
The research, Demographic consequences of migratory stopover: linking red knot survival to horseshoe crab spawning abundance, was authored by Conor McGowan (USGS), James Hines (USGS), James Nichols (USGS), James Lyons (U.S. Fish and Wildlife Service) and others.
It was published in this month’s edition of Ecosphere, a new open-access journal of the Ecological Society of America. The article is available online.