Future of horseshoe crabs in Delaware Bay in the cross-hairs, activists say
Fewer female crabs mean fewer eggs, which is bad news for red knot birds
| July 11, 2022
Horseshoe crabs, those crawly creatures that look like they belong in an “Alien” movie, have survived for hundreds of millions of years. But now, their population in the Delaware Bay is threatened because of proposed new rules allowing more of them – particularly females — to be killed to meet a growing commercial demand for their unique biological makeup, activists say.
Tied to the crabs’ fortunes is a species of migratory shorebirds listed as threatened under the Endangered Species Act, the red knot, that rely on the crabs’ eggs for a major source of nourishment during their migration.
How this delicate balance between the crabs and birds plays out will be determined in the months ahead by a multistate agency that oversees the management of more than two dozen species of nearshore fish along the Atlantic coast.
The agency’s name – the Atlantic States Marine Fisheries Commission, which includes representatives of 15 states as well as fishing industry interests — does not exactly roll off the tongue but it has an important say about the vitality of the crabs’ future in the Delaware Bay.
Wildlife and environmental activists argue that if the commission finalizes a recommendation it received in January to roll back a years-long prohibition on harvesting female crabs, it will hurt the horseshoe crab’s population but also have long-lasting harmful effects on the red knot.
Fewer female horseshoe crabs mean fewer horseshoe crab eggs and diminished rich sources of food for the red knots, which stop in the Delaware Bay during their migration of more than 9,000 miles from Tierra del Fuego at the southern tip of South America to breeding grounds in the Arctic Circle. (Think of the red knots as marathoners carbo-loading on pasta the night before the big race.)
Harvest opponents say that, in turn, means the red knot, which once reached a population high in the Delaware Bay of 72,000 but bottomed out to 6,800 in 2021, will be further imperiled.
Christian Hunt, the southeast representative for the conservation group Defenders of Wildlife, said horseshoe crabs are popularly used for bait in the fishing industry, particularly for eel and whelk.
“There’s just something about the smell of horseshoe crabs themselves that set off the animals being fished,” he said, adding that efforts to create synthetic alternatives have been unsuccessful.
The crabs’ blue blood is also harvested for biomedical purposes to produce something called LAL (Limulus Amoebocyte Lysate), which is used to detect harmful bacterial contamination in vaccines, intravenous drugs and medical devices.
Larry Niles, a wildlife biologist with Wildlife Restoration Partnerships, criticized the commission for allowing aquatic life to be commodified, saying the estuary’s productivity has been capitalized “for the sake of a few investor-owned corporations.”
Each year, the commission has relied on a model that estimated the abundance of horseshoe crabs and red knots in the Delaware Bay region to select one of five possible “harvest packages” for horseshoe crabs to be used in the bait industry.
Each year, the model has selected the same package: 500,000 males and zero females, Hunt said, adding, “It was agreed that the prohibition wouldn’t be lifted until the Delaware Bay region hosts at least 81,900 red knots or 11.2 million female horseshoe crabs. Neither has occurred yet.”
Under a proposed management plan presented in January, up to 190,000 female crabs could be harvested as soon as 2023.
Delaware Bay uniquely attractive
Though horseshoe crabs are known to populate areas from New Hampshire to Florida, the Delaware Bay is particularly attractive for them, Niles said.
The bay is comparatively underdeveloped and its shallow muddy areas allow the water to heat up to 59 degrees, a temperature that triggers spawning, he said. But over time, the density of crab eggs has declined. In the 1980s and 90s, researchers reported 50,000 eggs per square meter. That number has recently dropped to as low as 7,000, Niles said.
(Read more from Delaware Currents about how researchers count horseshoe crabs in the bay.)
In what Niles described as “a very delicate dance,” red knots arrive in May and June, timed to coincide with a bounty of crab eggs. Over the course of several nights, a female crab can lay more than 100,000 eggs, each of which are the size of a pinhead. Each bird needs 180 grams, or 400,000 eggs, to bulk up to finish its migration.
In 2020, for reasons that are unclear, the waters for the crabs to spawn were unusually cool, which suppressed egg production.
“Birds were bouncing around, trying to find eggs to feast on and they found nothing and they just left,” Niles said.
Predictions based on fuzzy math, critics say
While harvest opponents say crab and bird numbers are out of balance and the proposed harvesting figures are based on shaky premises, Tina Berger, a spokeswoman for the commission, defended the model.
She said it was developed collaboratively with red knot and horseshoe crab scientists from the U.S. Geological Survey, U.S. Fish and Wildlife Service, academia and state agencies and approved by an external, independent peer review panel.
“The data are consistent with those used in the past modeling framework, if not more comprehensive than before,” she said. “The data used are the best available data and no relevant data were provided and excluded.”
But Hunt said the commission, in reaching this proposal, relied on surveys “long considered biased and of dubious accuracy.”
“With the red knot on the very edge of extinction, it shows just how out of touch the ASMFC has become,” Hunt said. “Now is the time to double down, not diminish, horseshoe crab protections.”
The U.S. Fish and Wildlife Service, which is a member of the commission, said in a minority report that the “risk and uncertainty are both too high for the resumption of female crab harvest at this point in time.”
Steve Cottrell, president of the Delaware Audubon Society, said the commission relied on a prediction about the crab’s population known as an adaptive resource model.
“To reach that new quota, it changed its input to include data from a new set of surveys, which show an increasing horseshoe crab population,” he said. “The previously used model used a survey that was horseshoe crab-specific, and that survey showed no increase. In other words, the ASMFC cherry-picked the data it used for its new model so that it would give the desired output, which is to allow for an increased harvest.”
Berger said the model was designed to manage a balance between the horseshoe crabs, their eggs and the shorebird population.
“Under the management of horseshoe crabs using the ARM model in the past decade, the passage population of red knots has been fairly stable but lower than desired, while the population of horseshoe crabs has increased,” she said.
She said other factors, including climate change, breeding conditions in the Arctic, habitat loss, or even timing mismatch between the birds’ migration and food availability, could account for the reduced number of red knots.
What happens next
Before the new harvesting framework can be used in the bay, an addendum will be drafted, reviewed and released for public comment, Berger said.
“The board recognized that there is considerable public concern about the potential impact on the threatened red knot population and the commission is committed to fully vetting its use for setting harvest levels through the public comment process over the next several months,” she said.
If the draft addendum is approved in early August, the public will be given at least 30 days to comment in writing or at public hearings.