Unexpectedly, this spring’s northbound migration saw the lowest number of red knots ever recorded on Delaware Bay beaches, deepening concerns about the shorebird’s long-term survival and undermining a quarter-century of conservation efforts.
New Jersey and Delaware conservationists counted fewer than 7,000 rufa subspecies of the bird during extensive surveys on land, air, and water in May. About a third of the population in 2020, less than a quarter of the previous two years’ levels, and the lowest number since the early 1980s, when the population was around 90,000.
The bird’s population was already far below what was needed to ensure its survival. New Jersey banned the harvesting of horseshoe crabs, whose eggs are essential for the birds’ long-distance migrations, after years of conservation efforts.
In addition to making it more vulnerable to external shocks like bad weather in its Arctic breeding grounds, the latest drop makes the rufa subspecies—which has been federally listed as threatened since 2014—closer to extinction, naturalists say.
According to Rutgers University biologist Joanna Burger, “we need to think about the red knot as a species that is dying and we really need emergency measures.” Since the early 1980s, she has studied the knot and other declining shorebirds like ruddy turnstones and semipalmated sandpipers on the Delaware Bay.
She demanded that the Atlantic States Marine Fisheries Commission put an end to the practise of harvesting horseshoe crabs for bait, which is still practised in Delaware, Maryland, and Virginia. According to wildlife experts, female crabs are not allowed to be harvested, which has resulted in the loss of some egg-laying crabs and a decrease in birds’ food supply.
In the wake of the new decline, naturalists have stepped up their calls for pharmaceutical companies to stop using LAL, an extract from the blood of the crabs that is used to detect bacteria in vaccines, drugs, and medical equipment. Horseshoe crabs have long been sought after because of the lack of synthetic alternatives, such as rFC, which is being used by at least one pharmaceutical company.
Conservationists estimate that up to a third of the crabs that are returned to the ocean after bleeding die or are unable to reproduce. Because of long-term declines in egg supply, there were plenty of crab eggs on the bay beaches this year, but the birds’ numbers have been severely depleted by natural disasters.
For the past 25 years, Larry Niles, a wildlife biologist working independently, has been trapping, monitoring, and counting shorebirds on the bay beaches of New Jersey. He was surprised by the magnitude of the decline in this year’s red knot count, which he attributes to signs of a poor breeding season in 2020.
During the 2020 migration, he believes that low ocean temperatures in the mid-Atlantic are to blame. Horseshoe crab spawning was delayed until early June because of the cold water, but by then the birds had already left Delaware Bay in an attempt to finish their migration.
At only 4.7 ounces when mature, many of the avian species have already succumbed to starvation after flying from Tierra del Fuego in southern Argentina. To get to the Delaware Bay, some fly nonstop for seven days before spending two weeks there resting and gaining weight.
In contrast to the previous year, when many birds failed to find food in the bay, they headed north in search of breeding grounds. Dr. Niles estimated that 40% of last year’s migrants died before they reached the Arctic because they had exhausted their reserves of food and water.
Peregrine falcons have also been blamed for this year’s decline in numbers, thanks to the construction of nesting platforms in New Jersey. As a result, it becomes more difficult for shorebirds to feed and gain weight on the bay beaches.
A complete ban on the harvesting of female horseshoe crabs until the population recovers is the best hope for the species’ survival, according to Dr. Niles.
According to him, “Rufa knots, especially long-distance red knots, could be lost.” Despite the fact that bad weather and cold water can’t be prevented, horseshoe crabs can be increased in numbers, allowing birds to find an abundance of horseshoe crab eggs in most of these conditions.