Population characteristics of prawns in natural and selective stocking systems (TH 103)

Shrimps are extremely valuable resources, in view of their large domestic as well as export demand. Their high value emphasizes the importance of resource management, especiaJly, since substantial increase in global shrimp production is not expected, to make roost efficient use of the stocks in existing fisheries. However, shrimp management is somewhat different in concept than management of other fisheries, owing to its unique life history. The important biological characteristic of penaeids is the presence of two distinct phases in their life cycle, involving postlarval and juvenile phase living close to inshore waters or in estuaries which serve as their nursery and an aduh phase in deeper waters, where they mature and spawn. Different species spend variable amount of time, ranging from few weeks to several months in their nursery habitats. The open estuary and tidal ponds of Cochin, where traditional prawn fisheries exist are ideal nurseries for prawns. Fishery of the tidal ponds involves trapping wild seeds during nursery phase and allowing them to feed naturally and grow till they emigrate when they are caught in filtemets. Tidal ponds are generally extensive in nature with little or no management. These habitats, however, provide a potential and biologically healthy environment for the growth of prawns and fishes. In seasonal ponds, paddy and prawn are cuhivated ahemately. Paddy is cuhivated during monsoon, when salinity becomes low. After paddy harvesting in October, prawn and fish seeds are allowed to enter the field during high tides. Harvesting starts in November and is carried out fur 6-7 days around every full and new moon. The process of trapping and filtration continue till the middle of April, when ponds are drained and the entire stocks were harvested. Perennial ponds are non-drainable and filtration is carried out round the year. However, occasional partial harvesting is resorted, when any calamities struck or large proportion of good-sized prawns encountered in the catch. Shrimp fishery of tidal ponds is supported mainly by M dobsoni, P. indicus and M monoceros. Despite, having many biological features in common, like backwater nursery phase, variations are expected to occur in the degree to which the brackishwater environment is put to use by each species and their distribution