Many thanks to all who provided info about the Horseshoe Crabs.  Maurice 
Barnhill provided this excellent info, plus a great web-site.
    ""The UD Marine College has a nice web site at
<http://www.ocean.udel.edu/horseshoecrab/>, which has viewing notes at
<http://www.ocean.udel.edu/horseshoecrab/History/eastCoastAdv.html>.
They say times of full and new moons, which actually fits better with my
recollections than the highest-tide (new moon) times only that I
mentioned in my first EMail.  That would be somewhere around June 1,
which might be the best time if water temperatures are normal this year.""

Jim Wilson
Queenstown