Horseshoe Crabs

Horseshoe crabs are often called “living fossils” because fossils of their ancestors date back almost 450 million years–that’s 200 million years before dinosaurs existed and 65 million years AFTER Dinosaurs became extinct. Horseshoe crabs are not true crabs at all. They are more closely related to arachnids (a group that includes spiders and scorpions) than to crustaceans (a group that includes true crabs, lobsters, and shrimp). Their eggs are an important source of food for some shore birds. Some of these shore birds make a 9,000 mile migration from their wintering grounds along the southern tip of South America to their breeding grounds in the Arctic tundra. Their journey is timed so they can take a rest along the shores of Cape Cod in order to feast upon this large concentration of Horseshoe Crab eggs. Shorebirds will spend approximately 2 weeks dining on the eggs in order to double their body weight and replenish the fuel reserves needed to continue with their long journey to the Arctic.

Unfortunately this natural phenomenon is in peril as the number of Horseshoe Crabs in the waters of Cape Cod have dramatically decreased over time. In fact, in many parts of the east coast Horseshoe Crab populations have declined by 90% over the last 15 years mostly due to over harvesting and habitat degradation. Huge numbers are crushed and used for fish bait since fish are attracted to the eggs. As the number of Horseshoe Crabs have decreased, so have the number of eggs available for consumption by migrating shorebirds. Shorebird population numbers are therefore plummeting as well, as many cannot gain the amount of energy needed to complete their migrations. As an example, the Red Knot bird has been placed on New Jersey’s Endangered Species list and many other shorebirds are in danger of being placed on that list if horseshoe crab populations are unable to rebound. Unlike other places in the USA, Cape Cod has not taken steps to protect the remaining Horseshoe Crab population.