The number of red knots visiting the beaches of Delaware Bay during this spring’s north migration unexpectedly dropped to its lowest level since counts began nearly 40 years ago, adding to concerns about the survival of the shorebird and a sharp setback for a quarter of a century his efforts meant to save him.
Conservationists found fewer than 7,000 of the bird’s rufa subspecies in extensive land, air and water counts on the New Jersey and Delaware side in May. The number is about a third of that found in 2020; less than a quarter of the level for the past two years; and the lowest since the early 1980s when the population was around 90,000.
The numbers were already well below the level that would ensure the bird’s survival. A previous decline had been halted by years of conservation efforts, including a New Jersey ban on harvesting horseshoe crabs, the eggs of which provide essential nourishment for birds on their long-distance migrations.
The recent decline is making the Rufa subspecies – which has been endangered at the federal level since 2014 – even more susceptible to external shocks such as bad weather in their Arctic breeding areas and bringing them closer to extinction, say naturalists.
“I think we need to think about the red knot as a dying species, and we really need immediate action,” said Joanna Burger, a biologist at Rutgers University. Since the early 1980s, she has been studying the knot and other deciduous shorebirds such as ruddy turnstone and semi-palmate sandpipers in Delaware Bay.
She called for an immediate ban on the fishing of horseshoe crabs as bait, an industry that still operates in Delaware, Maryland and Virginia and is subject to quotas from the Atlantic States Marine Fisheries Commission. Although regulators do not allow female crabs to be harvested, naturalists say the rule will not be strictly enforced, resulting in the loss of some of the egg-laying animals and a consequent reduction in the birds’ food supply.
The recent decline also fueled calls by naturalists to urge the pharmaceutical industry to stop using LAL, an extract from the blood of crabs used to detect bacteria in vaccines, drugs and medical devices. A synthetic alternative, rFC, is available and used by at least one pharmaceutical company, but the industry as a whole has been slow to embrace the new technique, resulting in continued demand for horseshoe crabs in the bay.
Although the crabs are returned to the sea after bleeding, conservationists believe that up to a third will die or be unable to reproduce. Ironically, there were plenty of crab eggs to eat on the beaches of the bay this year, but a long-term decline in egg availability has severely dented the bird population and thinned any cushion that would allow the species to survive natural hazards.
Larry Niles, an independent wildlife biologist who has trapped, monitored, and counted shorebirds on New Jersey’s bay beaches for the past 25 years, said he expected this year’s red knots to decline as there was evidence of a bad breeding season in season 2020 but shocked at the size of the decline.
He said it was likely due to low sea temperatures in the mid-Atlantic during the 2020 migration. The cold water delayed spawning of the horseshoe crabs until early June, when the birds had already left Delaware Bay to complete their migration.
Many of the birds, weighing just 4.7 ounces when fully grown, are emaciated after flying from Tierra del Fuego in southern Argentina on one of the longest bird migrations. Some fly non-stop for seven days before reaching Delaware Bay, where they usually stay for about two weeks to rest and gain weight.
But last year many could not find food in the bay and continued north to reach their breeding grounds. Dr. Niles estimates that about 40 percent of migrants died in the last year before reaching the Arctic simply because they ran out of energy.
In that year he also blamed the predation by peregrine falcons, whose growing coastal population was supported by the construction of nesting platforms in New Jersey. They often hunt over the beaches of the bay, making it harder for flocks of shorebirds to feed and gain weight.
The best hope for the species’ survival lies in a complete ban on harvesting female horseshoe crabs until the crab population has recovered, said Dr. Niles.
“Rufa nodes, especially red long-haul nodes, could be lost,” he said in a message to supporters. “We can’t stop bad winds or cold water, but we can increase the horseshoe crab population so that birds that arrive in most of these conditions will find an abundance of horseshoe crab eggs.”