Fish population size estimates from a small intermittently open estuary inSouth Africa, based on mark-recapture techniques

Population sizes of the migratory marine-spawning fishes in the small inter mittently open East Kleinemonde Estuary (33-32'S,27 degrees 03'E) were esti mated during two independent mark recapture studies between 1994 and 1996. Seines were used to sample fishes during the closed-mouth phase of the estu ary. All individuals above a stipulated minimum size were marked by fin-cli pping. Population estimates were obtained by use of two mark recapture mode ls ( Schnabel and a maximum-likelihood estimator) and a derived method. The total population size was estimated at similar to 18 000 and similar to 13 3 000 individuals during the two study periods respectively. The large temp oral ( interannual) variability was ascribed to both abiotic ( estuary mout h conditions) and biotic -conditions. The dominant species during both peri ods was Rhabdosargus holubi, which accounted for similar to 75% and similar to 80% of the total population of marine fishes in the estuary. The succes s of this species is attributed to an extended breeding season and the abil ity to recruit during mouth overwash events.