According to an independent annual survey, the number of rufa red knot shorebirds migrating through Delaware Bay beaches to Arctic breeding sites this spring reached a four-year high. The survey conducted by land and boat counted approximately 22,000 of these robin-sized birds, which is an encouraging sign considering their federally threatened status. This number represents a significant increase from the record low of 6,880 birds in 2021. Larry Niles, an independent biologist who has been monitoring the migration of the rufa red knot for the past 25 years, shared these findings.
Dr. Niles attributed the healthier population of birds to the relatively warm ocean waters, which facilitated the spawning of horseshoe crabs. The eggs of these crabs are a crucial food source for the red knots. The birds spend a week or two gorging on the crab eggs in May, allowing them to regain weight after their long-distance flights from places as far away as Tierra del Fuego, Argentina. This migration is one of the longest in the avian world.
During this year’s migration in May, the density of crab eggs on the beaches bordering New Jersey and Delaware rose to about 10,000 per square meter, compared to a recent low of around 5,000. Dr. Niles explained that the birds initially stayed away when they found no eggs but returned when they discovered the presence of eggs.
Dr. Niles expressed his elation at the sight of 22,000 birds this year, but he also noted that both the shorebird population and the crab egg population are still well below their historic norms. In the 1980s and early ’90s, the bay beaches typically hosted around 90,000 birds and 50,000 to 100,000 eggs per square meter. Over-harvesting of horseshoe crabs in the late ’90s and early 2000s caused a decline in the bird population and raised concerns about the potential extinction of the rufa red knot.
Efforts to protect both the birds and the crabs have faced challenges due to inconsistent estimates. The U.S. Fish & Wildlife Service, which uses modeling, considers the red knot population stable at around 42,000 over the past four years. On the other hand, the Atlantic States Marine Fisheries Commission relied on the federal agency’s estimate when considering the restart of female crab harvesting in the bay but ultimately decided against it. The commission cited the potential for inflated estimates resulting from the agency’s modeling method. However, the Fish & Wildlife Service disagreed with this view.
The agency published a commentary in May, stating that there is no evidence of recent declines in the overall number of rufa red knots, pointing to a “low but stable” wintering population in Tierra del Fuego. The agency plans to issue a new estimate for the number of birds passing through Delaware Bay this spring in the fall.
The agency, along with its state partners in New Jersey and Delaware, undertakes aerial surveys and on-the-ground observations to create a model of the total stopover population. In 2021 and 2022, the two counting methods diverged significantly. While aerial counts reported the lowest populations on record, the observation-based model showed little change from previous years. The agency stated that the reasons for these discrepancies are not yet clear, suggesting that aerial counts may become less reliable over time and personnel changes could contribute to the variations.
In April, the agency released a long-term recovery plan for the red knot, focusing on protecting its habitat, ensuring an adequate food supply, and addressing sea-level rise. The plan followed a federal judge’s ruling that banned horseshoe crab harvesting from March 15 to June 15 this year on about 25 islands off South Carolina, where approximately two-thirds of the knots stop during migration. The ruling also temporarily prohibited certain fishing companies from harvesting horseshoe crabs for biomedical purposes, including the testing of medical products like vaccines. The order aimed to prevent the depletion and harm of horseshoe crabs.
During this year’s stopover along the Delaware Bay shores, almost all the counted knots (excluding about 2,000) were found on the New Jersey side. This is attributed to the closure of New Jersey’s beaches during the migration season and the repair of dune breaches to prevent horseshoe crabs from being washed into coastal marshes during high tides. In New Jersey, the harvesting of horseshoe crabs has been banned since 2008 under state law, while regulated harvesting remains in effect in other states bordering the bay, including Delaware.
Steve Cottrell, the president of Delaware Audubon, a conservation group, stated that the significantly smaller number of knots on the Delaware side is mainly due to the ongoing crab harvest there. Despite the official ban on female crab harvesting by the Atlantic Fisheries Commission, a lack of enforcement has raised suspicions of illegal harvesting of female crabs alongside males. Cottrell emphasized that closing Delaware’s beaches will make no difference if horseshoe crab eggs continue to be absent during shorebird migration.
The Atlantic Fisheries Commission spokeswoman, Tina Berger, mentioned that enforcing quotas is the responsibility of the states and urged anyone suspecting violations to notify the appropriate state officials.
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