Geographic separation of stocks of the edible jellyfish Catostylus mosaicus (Rhizostomeae) in New South Wales, Australia

The population structure of the commercially harvested jellyfish Catostylus mosaicus (Scyphozoa, Rhizostomeae) was investigated in estuaries and bays in New South Wales, Australia. Variations in abundance and recruitment were studied in 6 estuaries separated by distances ranging from 75 to 800 km. P atterns of abundance differed greatly among estuaries and the rank abundanc e among estuaries changed on 5 out of the 6 times sampling occurred. Great variation in the timing of recruitment was also observed among estuaries. V ariations in abundance and recruitment were as extreme among nearby estuari es as distant ones. Broad scale sampling and detailed time series of abunda nce over a period of 2.7 yr at 2 locations showed no consistent seasonal tr end in abundance at 1 location, but there was some indication of seasonalit y at the second location. At Botany Bay, the abundance of medusae increased with distance into the estuary and on 19 out of the 30 times sampling occu rred medusae were found at sites adjacent to where rivers enter the bay. Me dusae were found to be strong swimmers and this may aid medusae in maintain ing themselves in the upper-reaches of estuaries, where advection from an e stuary is least likely. Variability in patterns of abundance and recruitmen t suggested regulation by processes occurring at the scale of individual es tuaries and, combined with their relatively strong swimming ability, suppor ted a model of population retention within estuaries. Populations of C. mos aicus in individual estuaries and saline lakes in New South Wales should, t herefore, be considered as separate stock units.