Threats to the Horseshoe Crab
During the first half of the 20th century, threats to the horseshoe crab included overharvesting primarily for fertilizer and animal feed. Large numbers of crabs were collected on mid-Atlantic beaches or in nets during the spawning season to meet this demand. However, most of the evidence of over-harvesting is anecdotal because historical data on horseshoe crab harvests is often incomplete. Watermen were not required to report their catch until the late 1990’s.
The threats to horseshoe crab populations have changed dramatically. Since the early 1990’s, horseshoe crabs have been harvested for bait to catch eel and whelk and are used for the biomedical industry. Most importantly, they have lost valuable spawning habitat to coastal development.
Horseshoe crabs are used as bait to catch American Eel (Anguilla rostrada) and whelk (Busycon spp.) in Maryland and the rest of the mid-Atlantic region. The increase in horseshoe crab harvests throughout the late 1990’s are a result of an expanding whelk fishery. Increasing demand for whelk in Asian and European markets was the driving force behind the expansion. For more information, visit the eel and whelk fisheries section.
Biomedical firms on the Atlantic coast catch thousands of horseshoe crabs to extract a biomedical product from their blood. After bleeding, the live crabs are returned to the sea. Recent studies have indicated that approximately 15% of the crabs harvested for this purpose may die from handling.
During 2000, a questionnaire distributed to the biomedical industry by ASMFC indicated that nearly 25% of the crabs landed for biomedical purposes were rejected for bleeding. Crabs are rejected generally because of an injury or that they were previously bled that year. For more information, visit the biomedical section.
Development of coastal habitat has increasingly become an important issue for horseshoe crabs. Sandy beaches are essential spawning habitat for horseshoe crabs and nearshore shallow water habitats (i.e., mud and sand flats) are important nursery grounds for juvenile crabs. Human activities can reduce the available habitat horseshoe crabs need for reproduction and larval development to maintain their populations over time.
Several types of shoreline erosion control structures commonly used to protect property reduce available spawning habitat. These structures include bulkheads, groins and rip rap. Each of these shoreline control structures commonly referred to as “armoring” or “hardening”, is designed to protect the shoreline from the effects of erosion. However, they also block access to spawning beaches, eliminate sandy beach habitat or entrap and strand spawning crabs during times of high wave energy. Coastal development activities combined with shoreline erosion are contributing to the continued deterioration of coastal habitats essential to spawning horseshoe crab populations. For more information, visit the habitat protection section.
or use the glossary located at the top of the page.
Raising Horseshoe Crabs in the Classroom
- Stacy Epperson
Aquatic Resource Education Dept
Department of Natural Resources
580 Taylor Ave., E-2
Annapolis, MD 21401