Mark-recovery methodology, accounting for mortality, enabled annual estimates of estuarine winter flounder (Pseudopleuronectes americanus) abundance at summer's end. Recruitment from the estuarine system to an inshore-offshore otter trawl fishery occurred incompletely (73%) over three age groups (II-IV). The release of tagged pre-recruits in two consecutive years and subsequent return data, adjusted for non-reporting of tag recoveries, yielded the following 1970 post-recruit, instantaneous mortality parameters: total = 0.3570, fishing = 0.2445, natural = 0.1125. A comparison of total recruitment from southeastern Massachusetts flounder groups, derived from a population estimate and instantaneous total mortality rate, with recruitment from the Waquoit Bay-Eel Pond system indicated that the latter constituted less than one percent of the total required to maintain equilibrium catch.