Management of jellyfish fisheries, with special reference to the O. Rhizostomeae

Recent catches of jelly fishes have exceeded 500 000 Mt yr super(-1) and almost all of the jellyfishes harvested are of the order Rhizostomeae. In this review we emphasise the peculiarities of managing a fishery for jellyfishes (cf. more traditional fisheries such as bony fishes). The review will discuss single-species and multi-species concerns about the exploitation of jellyfishes. The population dynamics of jellyfishes are complicated. A substantial proportion of the life history of these organisms is spent as benthic polyps (and associated asexual forms) and fluctuations in abundance of medusae are great, partly because the medusoid stage is generally short-lived. Changes in biomass of edible jellyfishes, at timescales of weeks to years, are probably larger than for any other fishery. Uncertainty in a fishery is usually great if: the target species is short-lived; highly fecund; there is considerable variation in abundance; and a large proportion of the stock is aggregated. Jellyfishes meet all of these criteria for uncertain fisheries. There is considerable evidence that physical processes may influence stock abundance of jellyfishes (e.g. changes in salinity) and good empirical models may result for some jellyfish fisheries. Although it is known that changes in physical conditions may trigger strobilation, there are few data on other effects such as variation in the survival of ephyrae. Multi-species considerations are diverse and harvesting of jellyfishes may affect other fisheries. Jellyfishes may respond to, and influence, nutrient loads. They may also have a major impact on benthic assemblages. We present a detailed case history on the fishery for Catostylus mosaicus in Australia. Evidence is provided that the stock units for C. mosaicus often may be small, on a scale of kilometres to tens of kilometres (especially in semi-enclosed water masses, i.e. saline lakes and semi-enclosed estuaries) and patterns of distribution of other species of edible jellyfishes worldwide suggest restricted distributions. Small stocks may be vulnerable to intensive fishing