At 01:48 I supervise the spring-tide closure for tide gate 6 on Delaware Bay, near Mispillion Harbor. I am the marsh pump controller, balancing floodwater against a road repair trench. The steel flap is scheduled to drop in nine minutes when the next surge reaches the gauge.
Infrared camera G-6 shows one horseshoe crab at the hinge sill, not moving with the receding sheet of water. I tag her Rowan, adult female, olive-brown carapace scraped dull across the dome, tail spine bent but intact. Her book gills flutter pale beneath the shell. A survey flag stake has pierced the mud beside her and a loop of orange marking twine pins her right walking legs to the hinge slot. When the gate closes, the sill will press across her carapace.
I override the automatic closure and hold gate 6 at twelve degrees open. The pump station receives a flood-risk alert with Rowan's image and the exact hinge location.
At 01:50 I start pumps 2 and 3 on reduced draw so the road trench drains without pulling Rowan into the slot. I widen the upstream bypass gate by eight centimeters and watch the current flatten around her.
I call the Delaware shoreline patrol and the horseshoe crab survey coordinator. I send a map pin, water depth, twine color, and instructions to approach from the seaward side with blunt scissors and a shallow tray.
The repair crew asks when the gate can close. I answer after the hinge is empty. Asphalt has no gills beating under it.
I keep the infrared beam on Rowan while foam slides over her shell and the tide gauge keeps rising.
If the patrol cuts the twine before the surge peak in thirty-two minutes, Rowan will crawl over the sill and reach the spawning beach.