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Delaware Bay red knot stopover is dying

July 8, 2022

The press release of the Department of Natural Resources and Environmental Control, published on July 1 in the Cape Gazette and titled “Growing horseshoe crab population supports migratory shorebirds,” leaves the reader with the unrealistic impression that all is well for an imperiled species of wildlife, the red knot. The iconic bird, for which Delaware is best known, is listed as a threatened species under the federal Endangered Species Act, and it is showing no signs of recovery.

The article claims that 40,000 to 50,000 red knots stopover annually in the Delaware Bay. These are virtual estimates based on a mathematical model using mark-resight methods that few biologists fully understand. The virtual numbers do not correlate with actual aerial and ground counts. Long-term studies show the rufa red knot population declined 90%, from 150,000 in 1980 to 16,000 in 2010. What the model does show is that there has been no population change between 2011 and 2021. It also shows that red knots are staying in the Delaware Bay for shorter time periods. If nutrition requirements are not met in the bay, the birds must forage elsewhere for less-beneficial prey.

Although the article correctly states that horseshoe crab egg availability is the most critical factor affecting the red knot population, the model inexplicably does not include the key egg density factor. Historically, there were 50,000 eggs per square meter on the surface of Delaware bay beaches during the month of May. In 2022, there were about 7,000 eggs per square meter during the same month.  

Although the existing bait harvest of horseshoe crabs in the Delaware Bay is preventing any semblance of recovery of the red knot, the Atlantic States Marine Fisheries Commission is advocating for an expansion of the harvest to include 500,000 females, suspiciously at the behest of a niche fishing industry. This position is in defiance of the fact that such an action would further imperil the federally listed red knot. To justify the new position, the commission cherry-picked additional non-selective horseshoe crab survey data to include in its model, since the previously accepted trawl survey data consistently showed no population increase.

A 2000 economic assessment of the Atlantic coast horseshoe crab fishery by the U.S. Fish and Wildlife Service estimated the annual economic value for New Jersey from visits to the Delaware Bay by wildlife enthusiasts during spring horseshoe crab spawning and shorebird migration ranged between $2.6 million and $3.9 million, in 1999 dollars. The analysis contributed to New Jersey’s decision to implement a horseshoe crab bait harvest moratorium in 2008. The economic value to Delaware from spring ecotourism can be assumed to be comparable. 

The New Jersey moratorium decision contributed immeasurably to the survival of the red knot. Unfortunately, Delaware continues to allow a horseshoe crab bait harvest, complicating red knot recovery. By continuing to allow a horseshoe crab bait harvest before red knots show clear signs of recovery, Delaware risks losing the economic benefits of being an attractive destination for a growing ecotourism market. It also risks losing the valuable environmental assets that a healthy ecosystem brings to the Delaware side of the bay.

Steve Cottrell
President, Delaware Audubon Society 
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