Volunteers on Reeds Beach in Middle Township, N.J., sifted through nets that temporarily trapped shorebirds so that they could be counted, tagged, weighed and measured.CreditCredit
By Jon Hurdle
Photographs by Michelle Gustafson
REEDS BEACH, N.J. — On a recent spring day at this remote beach, hundreds of shorebirds flapped frantically beneath a net trapping them on the sand. Dozens of volunteers rushed to disentangle the birds and place them gently in covered crates.
On a nearby sand dune, teams of scientists and volunteers attached metal leg bands, plastic tags and tiny radio transmitters to birds of three species. They were weighed and measured, and then released.
The operation is part of an annual “catch” of migratory shorebirds that stop on the beaches of the Delaware Bay, a globally important bird habitat, to gorge on the eggs of spawning horseshoe crabs. The stopover strengthens the birds for the long-distance migration to the Canadian Arctic, their breeding grounds, from as far away as southern Chile.
With fresh information on the birds’ weight and health, the scientists will be able to judge whether these species are getting enough food to reach their breeding grounds, and whether their populations are stable.
One of them, the red knot, has been listed as a threatened species. Since 2000, red knot numbers have plunged as low as 10,000 in some years, around one-ninth of the level in the 1980s. At the moment, the population hovers at about 30,000, still too low to be sustainable, conservationists claim.
Additional challenges like severe Arctic weather during breeding, or coastal development along the migration route, could lead to the bird’s extinction. Populations of other migratory shorebirds, like semipalmated sandpipers and ruddy turnstones, have also declined.
The problem, conservationists say, is the overfishing of horseshoe crabs for commercial fishery bait and the harvesting of the animals for their blood, which contains an extract called L.A.L., used by the biomedical industry to detect certain bacteria.
Now, conservationists are renewing calls to halt the harvest for bait altogether, and to persuade the biomedical industry to switch to recombinant Factor C (rFC), a synthetic alternative to LAL, to ease pressure on the horseshoe crab population.
“The only responsible thing to do here is a moratorium,” said Eric Stiles, president of New Jersey Audubon, an environmental group leading the initiative.
Recognizing the threat to the birds, the Atlantic States Marine Fisheries Commission, an interstate regulator, banned the harvest of female horseshoe crabs for bait starting in 2013, in the hope that a recovering population of females would lay more eggs and allow the birds to rebound.
While the commission maintains there has been an increase in the number of crabs since the ban, neither the crabs nor the red knot has recovered to the levels seen before the fishing industry’s unprecedented removal of the crabs from the bay in the 1990s.
The commission’s critics blame poor enforcement of the ban and the continued harvest of thousands of crabs for bleeding, which is estimated to kill at least 15 percent of them and may prevent the survivors from reproducing.
Crabs taken for bleeding are not included in the commission’s quotas, and their numbers and mortality rates are not published because the companies that collect the blood want the figures kept confidential.
Conservation groups are urging officials in Delaware, Maryland and Virginia — three bay states that use crab quotas — to ban the horseshoe crab harvest until there’s a full recovery of both crabs and birds. (New Jersey, the other state bordering the bay, imposed a moratorium in 2008.)
Banning the harvest, advocates argue, would rebuild a crab population that is essential not only to the birds but also to depleted marine species, such as weakfish, that feed on the crabs and in turn support commercial and recreational fishing on the bay.
“It’s not just about the birds,” said David Mizrahi, vice president for research and monitoring at New Jersey Audubon. “It’s about the whole ecosystem.”
Within the knot population, the biggest decline has been seen in long-distance migrants that spend the northern winter in Tierra del Fuego, in southern Chile. That population numbered only 9,840 in 2018, down 25 percent in the last year and less than a fifth of the number in 2000.
Scientists say those birds are especially sensitive to a shortage of horseshoe crab eggs on Delaware Bay beaches, as they are emaciated when they arrive from South America.