I don't clam, but looking at the maps, it does not look like there are too many open areas north of IBSP area that would be conducive to clamming. ...And yes, from my understanding, clamming spots are even more secretive than fishing spots. Olclamman, used to post of his trips to IBSP and even mentioned "blindfolds" when bringing friends
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NJDEP Clamming MapsRemember no clamming on Sundays, either
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Good luck. Maybe someone else may have more information for you.