NATURE - USA

A Bird, a Crab and a Shared Fight to Survive

 

A captured red knot is weighed by a volunteer on Reeds Beach in Cape May Court House, N.J. The East Coast red knot population has plummeted. More Photos »

CAPE MAY COURT HOUSE, N.J. — Like clockwork, the red knots arrive every spring, descending on the beaches of Delaware Bay to feast for a few weeks on horseshoe crab eggs and, in the process, double their body weight. The knots are delicate, robin-size shorebirds named for their salmon coloration and renowned for their marathon migration — more than 9,000 miles each way, from the southern tip of South America to the Canadian Arctic.

 

 

Horseshoe crabs come to shore to lay their eggs on the sand. Red knots feast on the eggs, and in the process double their body weight. 

Horseshoe crab eggs on Reeds Beach in Cape May Courthouse, N. J. More Photos »

That migration is fueled by an ancient synchronicity — the spawning of billions of tiny green horseshoe crab eggs just as the knots and their prodigious appetites arrive — that is now threatened. Largely because of the overfishing of horseshoe crabs for bait (they are a favorite of conch fishermen), the East Coast red knot population has plummeted. Their numbers have dropped from more than 100,000 in the 1980s to only about 30,000 today, and wildlife biologists in New Jersey worry that without stronger protections, they could vanish. But that depends on the crabs.

“The recovery of the birds can’t really start until there are more crabs,” said Lawrence J. Niles, a biologist with Conserve Wildlife Foundation of New Jersey and a former official with the State Department of Environmental Protection. “We can’t wait decades. We need more crab eggs now.”

In recent years, as reliably as the red knots themselves, Dr. Niles has returned to the beaches here with Amanda D. Dey, principal zoologist for the Department of Environmental Protection. (Dr. Dey also happens to be Dr. Niles’s wife.) Together with a team of volunteers, they monitor the red knot arrivals and gauge the robustness of the crabs’ spawn, a slow-motion coupling in which several males usually go after a single female. Though lacking the passion, perhaps, of the famous beach scene in “From Here to Eternity,” it is still strangely compelling.

New Jersey has moved to protect both species, imposing a ban on horseshoe crab harvesting a few years ago, and in February, officially listing the red knot as endangered. The crabs, however, ignore state lines.

After laying their eggs in Delaware Bay, they head out into open waters, traveling as far south as Maryland and Virginia, which have been less successful in protecting them. Delaware, which limits the annual catch to 100,000 male crabs, tried to end horseshoe crab fishing, but the ban was overturned in court. Maryland and Virginia have some restrictions on their fisheries, but numerical models suggest that any rebounding of the crab population is many years off.

Besides tracking the crabs, Dr. Niles and his team trap some of the birds to weigh, measure and band them before releasing them onto the beach here. On a recent afternoon, with a hot breeze blowing off the bay, the team waited hours for the tide to rise, edging a group of red knots, as well as ruddy turnstones and sanderlings, higher up on the beach. Suddenly, a boom sounded and a cannon buried in the sand fired a large net over the birds. The volunteers sprang into action, racing to collect the birds in large plastic boxes.

The measurements looked good. Calm waters and warm temperatures this spring have provided ideal spawning conditions for the crabs, which deposit their clusters of eggs on the sand. Throughout the spring, most of the red knots were gaining enough weight to sustain them during the rest of their journey to the Arctic and allow them to breed successfully.

“It’s like eating peanuts,” Dr. Dey said. “Horseshoe crab eggs are soft and full of fat, and the knots eat them as fast as they can pick them up. That’s what makes it such a critical resource.”

In fact, the conditions were so good this year that the majority of the red knot population on the East Coast parked itself here. Dr. Niles and Dr. Dey estimated that about 26,000 stopped there to feed, double last spring’s count.

But one banner year for Delaware Bay does not constitute a comeback, scientists say. Horseshoe crabs are not only popular as bait; they are also prized by the pharmaceutical industry for their copper-rich blood, which is used in laboratories to test drugs and devices for bacterial contamination. Hundreds of thousands of the crabs are collected on the East Coast each year for that purpose. They are returned to the water, but somewhere between 5 percent and 30 percent die.

The Atlantic States Marine Fisheries Commission monitors the use of crabs by the biomedical industry and has recently proposed establishing harvest levels for horseshoe crabs from Delaware Bay. The guidelines would use a complex formula that would take into account the abundance of both red knots and female horseshoe crabs.

Still, Dr. Dey believes that stronger safeguards are needed. While 30,000 red knots may sound like a lot, the population is vulnerable, whether at the hands of man or nature. “If you have 12,000 red knots in a location and 1,000 die because of red tide or an oil spill, that’s 10 percent of the population,” she said. “At these low numbers, anything can come in and knock out the birds.”