Previous Update
Yesterday Humphrey Sitters and I conducted the last count of shorebird roosts at the Cox Meadow and Egg Island Peninsula sites. A strong wind gusting to 30 knots blew from the northeast, normally too much for a bird survey. But it blew offshore so that we could motor WRP’s 17 ft Boston Whaler “Hanna” in the shelter of the leeward shore in both locations. To reach Cox Meadow, we launched at Jakes Landing and motored past East Creek and West Creek in relatively calm seas. At Egg Island Point, nearly 3 miles from the mainland, the unobstructed east wind and ocean swell from the mouth of the bay pushed high waves against the east-facing side of the wide peninsula of the marsh. We launched from Fortescue Creek into the lee waters of Egg Island, but at the Point, we could see the tumult of wind, tide, and ocean swell just across the slim Point.
Humphrey and I surveyed the western side of Egg Island Marsh while easterly winds aided the unobstructed ocean swell from the mouth of the bay. These conditions excerbated by sea level rise have eroded more than 1200 of the marsh since 1985.
During the trip, we saw about 1000 red knots and 3000 ruddy turnstones, 500 sanderlings far fewer birds than the last baywide count on the 26th, when we saw just over 22,000 knots and 12,000 turnstones. We saw most of the birds had left foraging sites the previous day, but in most years, birds staged in roosts, like Egg Island, while waiting for a favorable wind. But our trip proved the birds were mainly gone.
The bay and her horseshoe crabs provided a bountiful stopover this year. The conditions for spawning were almost ideal. Water temperature reached the rough threshold, eliciting spawning early in May, and stayed above throughout the spawning period. Susan Linder and her egg density study team reports egg densities in the last week of May above 19,000/square meter.
Horeseshoe crab surface egg densities 2015-2023. Each line represent a week in May ( 1-4). Graphic by Susan Linder
However, when birds need them most, the third-week egg densities were much lower at 4400 eggs/ meter square, lower than the last few years, and practically nothing compared to the time before horseshoe crabs were overharvested. In the 1980s, Karen Williams counted eggs for the NJ Endangered Species program while I was a biologist there. Her data was rediscovered by Joe Smith and published in his paper on Delaware Bay horseshoe crab egg densities. In 1986 Karen measured egg densities over 100,000/square meter. Even in the cold water year of 1987, egg densities reached 50,000/square meter. The short video by NJN in 1986 shows what egg densities of these magnitudes look like. You might think this kind of ecological largess belongs in another world. But we are closer than it appears.
Our team now conducts an experiment to describe how eggs reach these densities. Theo Deihl led a team to construct on three different beaches two fences that stretch into the sea from the high tide line to the low tide line. The fences are parallel in the upper beach but fan out into a wider width at the seaward end, funneling crabs into a smaller area, thus simulating a higher density of crabs. At these higher densities, we estimate a threshold exists where crabs saturate the beach with eggs, and each new female digging in her eggs digs an equal amount to the surface. We hypothesize as crabs lay eggs, the number on the surface slowly grows as crabs dig into other crabs’ egg masses. But at saturation, the density goes up fast, rapidly reaching densities seen in the ’80s and ’90s. With our experiment, we will document this relationship and use the data to argue to the agencies killing crabs to stop killing altogether and let the population of crabs restore to this ecological maximum, also called carrying capacity.
Egg saturation should be the focus of all agencies. Instead of managing for a peak of spawning, we should aim for a robust plateau that starts early and finishes late because the crab population is so large it takes that long for them to lay eggs. At that level, egg densities would be sufficient in all circumstances, like in 2003 and 2019, when cold water delayed the spawn. Or in the years when the Bayshore endures a week of onshore winds that interrupt spawning or in the future when warming waters accelerate the spawn earlier.
The season was a success because the crabs spawned without any adverse conditions. This might be a good enough target for agencies encouraging the killing of crabs. But managing the bay bird stopover demands egg saturation. This way, the birds can also find a home in the bay under any circumstances.
And why not do this because none of it goes to waste? In the 1970s and 80s, most of the horseshoe crab largess floated into the sea or remained buried in the sand. The excess surface eggs that will never hatch and the newly hatched young provided an ecological cornucopia of resources underpinning finfish productivity. It’s no accident that when Karen Williams measured 100,000 eggs/square meter, Fortescue called itself “The Weakfish Capital of the World.” It only makes sense.
This project is a result of goodwill and long-term financial support. Our entire team appreciates the National Fish and Wildlife Foundation for funding, NJ Fish and Wildlife for the Shorebird Protection Areas, Conserve Wildlife Foundation for Shorebird Stewards, the Wetlands Institute for “Return a Favor” volunteers, and most deliciously Citizens United to Protect the Maurice River for our nightly meals. Volunteers provide energy and a sense of purpose to those who work full-time, and our nightly meals allow us to survive the three weeks of intense work in relatively good humor. Birds, crabs, and people are grateful to all.
Fortescue, NJ, a small port in the center of Delaware Bay once boasted it was the “Weakfish Capital of the World”. Before the overharvest of horseshoe crabs and the destruction of the abundance they created in the 1990s, the town’s marinas, restaurants and sporting goods shops were filled with anglers from all over south jersey. Now the town marinas struggle to exist.
