Red Knots in a Bind

As horseshoe crab populations dwindle, species up the food chain are feeling the pinch.

You may have never thought twice about a horseshoe crab—or even once for that matter—but lately, people are noticing that perhaps they should. Having existed one million years before even the first dinosaurs walked the Earth, the horseshoe crab is considered a “living fossil” that has managed to thrive throughout the ages ... until recently.

Horseshoe crabs have been harvested for centuries to make fertilizer and farm animal feed, more recently being used for medical purposes and by fisheries for eel bait. With a slow maturity rate of eight to 10 years, the concern overfishing poses is often debated among conservationists as the cause of dwindling crab numbers. But the horseshoe crabs aren’t the only ones in jeopardy.

Each spring, red knots, a species of sandpiper about the size of a robin, make an incredible journey across more than 9,300 miles from Tierra del Fuego at the tip of South America to their breeding grounds in the Arctic. Along the way, the little birds stop to refuel at select sites referred to as “staging areas.” These massive flocks frequently return to the same staging areas every year, having coordinated their stopover in Delaware Bay with the horseshoe crab spawning period.

Delaware Bay is home to the largest population of these crabs, where the number of reproducing adults peaked in the early 1990s, but has been in decline ever since.

Shorebirds, especially red knots, rely on the billions of eggs produced when the crabs spawn along the shoreline each spring. The birds, arriving underweight and tired from a non-stop flight of as much as 5,000 miles, gorge on the eggs. It is critical that the red knots gain enough weight in those few weeks to continue the final 2,000-mile leg of their journey to the Arctic.

Having once numbered 100,000, according to the Delaware Shorebird Project, there are now typically around 20,000 red knots in Delaware Bay each spring. The US Fish and Wildlife Service suggests that “[t]he increase in taking of horseshoe crabs for bait in commercial fisheries that occurred in the 1990s may be a major factor in the decline in red knots.” Climate change affecting the Arctic and hunting of the birds in South America are also suspected as contributing factors.

Since 1997, the Delaware Shorebird Project, made up of a team of international scientists, researchers, volunteers and birders, has studied the red knots and worked to assuage the hazards they are facing. According to their website, “The sound management of the resources upon which shorebirds depend is vital to preserve this breathtaking, awe-inspiring natural cycle for our children and grandchildren.”

While the birds and crabs remain in peril, there are actions being taken by conservationists, state legislatures, and the Delaware Department of Environmental Protection to help ensure their recovery: Numbers of crabs harvested for eel bait have been limited, horseshoe crabs used for medical research are often returned to the Delaware Bay, and research to find an eel bait alternative is ongoing.

As the first red knots appear on the shoreline this coming year, so does a glimmer of hope for their future.

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