and staying the same
Here’s Why:
Horseshoe crabs are crucial to the Delaware Bay’s food chain and human industries. Although they have been historically overharvested, recent regulations and conservation efforts have stabilized their population and contributed to the ongoing recovery of this unique species.
Did you know the Delaware Bay is crawling with a prehistoric creature?
Atlantic horseshoe crabs (Limulus polyphemus) are marine arthropods – not true crabs like blue crabs or hermit crabs, but more akin to spiders and scorpions. They live on the ocean floor and have a lineage dating back 445 million years — older than the dinosaurs. These animals live on the east coast of the United States and Mexico, with the largest population worldwide in the Delaware Bay. They contribute significantly to the bay’s food chain and human industries. Historically, the fishing and medical industries overharvested horseshoe crabs, but populations have stabilized in recent years. This section discusses the negative influences on horseshoe crab populations, how these animals play an essential role in the food chain, and what people are doing to ensure their populations rebound.
Every spring, as water temperatures rise, these ancient mariners migrate to spawn on the sheltered, sandy beaches of the Delaware Bay. The females carry around 88,000 eggs and lay around 4,000 eggs per nest, depositing them about 6 inches into the sand to protect them from the reach of most shorebirds. This bounty of eggs provides a valuable food source for migratory birds like the red knot. The red knot’s survival hinges on the availability of horseshoe crab eggs, which deliver the energy-rich food critical for their 9,000-mile spring migration from Argentina to the Arctic Circle.
Of the thousands of eggs a single horseshoe crab lays each year, only about 10 will survive to adulthood. Juvenile crabs remain near their birthplace but progressively move into deeper waters as they mature. Notably, horseshoe crabs molt, shedding their old shell to accommodate their new growth. They reach reproductive maturity at 10 years and can live more than 20 years.
Humans have valued horseshoe crabs throughout history for diverse uses such as fertilizer production, livestock feed, and fishing bait. They’ve also played a vital role in the biomedical industry, including COVID-19 research. While most animals have red blood from iron, horseshoe crabs have blue blood containing copper. Scientists use the blood to produce Limulus Amebocyte Lysate (LAL), which they use to test medical products for bacterial contamination. However, this blood collection process can be fatal to crabs. The biomedical industry has explored synthetic alternatives to LAL to reduce its impact on the horseshoe crab population. The adoption of synthetic LAL by the commercial industry is pending product development and validation.
Overharvesting significantly depleted the number of horseshoe crabs in previous years. Nearly a million crabs were harvested annually between the 1850s and 1920s. Thankfully, since the early 2000s, harvest regulations and restrictions by the Atlantic States Marine Fisheries Commission (ASMFC) have helped stabilize the Delaware Bay horseshoe crab population. The ASMFC conducts a stock assessment every decade to evaluate the population, and the most recent one in 2019 found the population to be stable.
Despite these improvements, the recovery of the horseshoe crab populations is still gradual due to their long lifespan and delayed reproductive maturity. An ongoing debate exists on whether current population levels are sufficient to support the needs of migratory shorebirds. Yet, recent data indicates that better management measures and reductions of their use as bait have increased horseshoe crab numbers.
Several organizations, including the Atlantic States Marine Fisheries Commision (ASMFC) and National Marine Fisheries Service, are actively working to ensure the horseshoe crab’s continued survival.
The establishment of the Carl N. Shuster Jr. Horseshoe Crab Reserve, the reduction of horseshoe crabs as bait, and the biomedical industry’s efforts to minimize stress on crabs during blood collection represent efforts to aid horseshoe crab population recovery. Through continued diligence, we aim to keep the Delaware Estuary a thriving home for horseshoe crabs, preserving this unique species for generations.
CCMP STRATEGY H3.4: Protect and restore horseshoe crabs and their habitat
This horseshoe crab indicator status report is based on research compiled in the 2022 Technical Report for the Delaware Estuary and Basin (2022 TREB). Please refer to this document for more information.
