Estimates of the number of nesting female turtles are illustrated, using an instantaneous count (IC) procedure modified by sampling in space as well as time. Variations of the modified IC procedure are shown to be equivalent to four methods, including the strip transect (in time), the line intersect (in time), and quadrat sampling (in time), depending on the specific sampling variant utilized. Estimators for all procedures, as well as for similar ones, are derived, as are the variances of the estimates. The modified IC procedure is illustrated with estimated "arribada" (or arrival) sizes at Playa Nancite, Costa Rica. ARRIBADA, a computer program for analyzing either actual or simulated strip transect data from arribadas, is described briefly.