Diel and Tidal Variations of Larvae and Juveniles of Metapenaeus dobsonifrom Sundarbans Estuarine System, India

The Sundarbans Estuarine System (SES) is a mangrove dominated monsoonal, macrotidal estuarine system in the east coast of India and is one of the best nursery grounds for shellfish populations in this region. The early developmental stages of penaeid prawns prefer the estuaries to complete their bipartite lifecycle. The present study, conducted within the extremely difficult and challenging environment of the SES, is a pioneering attempt to decipher the probable diel and selective tidal variation patterns of different stages (mysis, decapodite and juvenile) of Metapenaeus dobsoniin the SES, India. The observations were conducted by selecting a time series sampling protocol of 72 hours each, during the spring and neap phases of the tidal cycle in the peak monsoon month of August 2014. During the spring and neap tides, the total population was observed to be dominated by juveniles (83%) and mysis larva (61%) respectively. The maximum abundance was observed to occur during the night time of the neap phase irrespective of tidal amplitude. During the spring phase the maximum abundance was recorded at low tide conditions irrespective of the diel variations. The increase in the abundance of mysis stages always synchronized with low tides during the neap phase whereas, the peak increase of juvenile abundance synchronized with the ebb currents (low tides) during the spring phase. M. dobsoniutilize the tidal currents for their ingress and egress mechanisms in order to travel horizontal distances or remain in their preferred habitats. Our study corroborated the significant importance of ontogenetic diel and a tidal variation of larval and juvenile’s abundance in the water column at SES. Such studies of the larval dynamics are very essential in the SES for estimating the fishery potential and sustainable management of wild seed collections by the local fishermen community.