The number of Red Knots visiting Delaware Bay beaches during this spring’s northward migration has unexpectedly fallen to its lowest level since counts began nearly 40 years ago, which has raised concerns about the survival of shorebirds and rolled back a quarter of a century of efforts to save it.
Environmentalists have found less than 7,000 of the rufa bird subspecies in extensive land, air and water counts on the New Jersey and Delaware sides of the bay in May. The number is about a third of that found in 2020; less than a quarter of the levels of the previous 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 survival of the bird. An earlier decline had been halted by years of conservation efforts, including a New Jersey ban on harvesting horseshoe crabs, whose eggs provide essential food for birds on their long-distance migrations.
The latest drop makes the rufa subspecies – listed on the federal endangered species list since 2014 – even more vulnerable to external shocks, such as bad weather in its arctic breeding grounds, and brings it closer to extinction, according to the researchers. naturalists.
“I think we have to consider the red knot as an endangered species, and we really need emergency measures,” said Joanna Burger, a biologist at Rutgers University. Since the early 1980s, she has studied red knot and other declining shorebirds such as ring-necked turnstones and semipalmated sandpipers in Delaware Bay since the early 1980s.
She called for an immediate ban on harvesting horseshoe crabs for bait, an industry still active in Delaware, Maryland and Virginia, which is subject to quotas by the Atlantic States Marine Fisheries Commission. Although the regulator does not allow the harvest of female crabs, naturalists say the rule is not strictly enforced, resulting in the loss of some of the laying animals and a consequent reduction in the bird’s food supply.
The new drop has also amplified naturalists’ calls for the pharmaceutical industry to stop using LAL, an extract from the blood of crabs that is deployed to detect bacteria in vaccines, drugs and medical equipment. A synthetic alternative, rFC, is available and is being 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 ocean after being bled, conservationists estimate as many as a third die or are unable to reproduce. Ironically, there were plenty of crab eggs to eat on the bay’s beaches this year, but a long-term decline in egg availability has severely damaged the bird population, thinning any cushion that would allow the species of surviving natural hazards.
Larry Niles, an independent wildlife biologist who has trapped, monitored and counted shorebirds on New Jersey Bay beaches for the past 25 years, said he expected the numbers of Knots this year due to signs of a poor breeding season in 2020, but was shocked at the extent of the decline.
He said this was likely due to the low ocean temperatures in the mid-Atlantic during the 2020 migration. The cold water delayed horseshoe crab spawning until early June when the birds had already left Delaware Bay in an attempt to complete their migration.
Many birds, weighing just 4.7 ounces at maturity, are already emaciated after flying from Tierra del Fuego in southern Argentina on one of the avian world’s longest migrations. Some fly nonstop for seven days before reaching Delaware Bay where they typically stay for about two weeks to rest and gain weight.
But last year, many were unable to find food in the bay, so they continued north in an attempt to reach their breeding grounds. Dr Niles estimated that around 40 percent of last year’s migrants died before reaching the Arctic, simply because they were low on energy.
This year, he also blamed predation by peregrine falcons, whose growing coastal population has been aided by the construction of nesting platforms by New Jersey. They frequently hunt on the bay’s beaches, making it more difficult for groups of shorebirds to feed and gain weight.
The best hope for the species to survive is a total ban on harvesting female horseshoe crabs until the crab population recovers, Dr Niles said.
“The Rufa knots, especially the long distance red knots, could be lost,” he said in a note to supporters. “We can’t stop the high winds or the cold water, but we can increase the horseshoe crab population, so birds arriving in most of these conditions find an abundance of horseshoe crab eggs.”