Shorebird Decline Linked to Using Crabs as Bait

A new study claims that the decline of the red knot , a shorebird, is connected to the use of horseshoe crabs for bait .

A shorebird commonly called the red knot seems to be in decline and a new study suggest the reason for this decline is the bait use of horseshoe crabs. Long-term surveys of red knots showed that the average weight of red knots when they leave Delaware Bay has declined significantly since their primary food source, eggs of horseshoe crabs, has been reduced. In addition, the study revealed red knot survivorship is related to departure weight, and that the population size of red knots has declined by more than 75 percent. "We concluded that the increased harvest of horseshoe crabs led to a reduction in the food supply for red knots at a critical period in their annual cycle, and this led to a dramatic decline in population size," said USGS scientist, Jon Bart, one of the authors of the study. Horseshoe crabs have been long harvested in Delaware Bay for use as bait in various fisheries. From 1992 to 1997, the reported harvest of crabs grew 20 fold from about 100,000 individuals harvested to more than 2 million. This study shows this increase in horseshoe crab harvest has led to a dramatic decrease in the number of spawning crabs and to a 90 percent decline in crab eggs available for shorebirds to eat. Delaware Bay is globally recognized as an important feeding stopover for migrating shorebirds, especially red knots. Each year, red knots migrate from Arctic breeding grounds to the southern tip of South America and back, covering more than 18,600 miles. In May, large numbers of red knots congregate in the bay during their northward migration where they gorge on horseshoe crab eggs in preparation for their continued migration to the Arctic. Lawrence Niles, a biologist with the Conserve Wildlife Foundation of New Jersey and senior author of the new study says, "Despite restrictions, the 2007 horseshoe crab harvest was still well above that of 1990, and no recovery of knots was detectable. Recovery of both horseshoe crabs and red knots may require more restrictions on horseshoe crab harvest, possibly even a complete moratorium for some period. We've proposed a program of adaptive management, including monitoring, that should result in the information managers need to find the right balance." Fifteen scientists participated in the study, from a wide variety of federal, state, and nongovernmental entities. The results are published in the February edition of the science journal Bioscience. The title of the article is, "Effects of horseshoe crab harvest in Delaware Bay on red knots: Are harvest restrictions working?"