The peak spawning day/night this year on the Delaware Bay will occur around sunset/full moon rise on May 25. The Delaware Bay is the best place in the world for observing horseshoe cab spawning. In the past, I have been at Slaughter Beach, Delaware which is the official horseshoe crab sanctuary (http://townofslaughterbeach.com/
), and gotten some very good photos see http://www.flickr.com/photos/david_ebert/6350787205/in/set-72157628018155771
for example). I am planning to be there again this year. If the weather is good and the crabs are out in number, the photography should be excellent because the full moon rises in the east a bit after sunset, so one can shoot the crabs well lite by the setting sun, shore and the rising moon in the east.