Monitoring green tiger prawn stock in Bushehr Province waters

The results of 30 months of trawl sampling on P. semisulcatus, De Hann 1848, obtained through operational phase of MONITORING GREEN TIGER PRAWN RESOURCES project, along with results of another available 28 months of the data of the same structure prior to this, has formed an invaluable time series of data as a proper basis for the further analysis. The survey area is located at North-west of the Persian Gulf from Bahrekan to Dayer waters. The ultimate goal of this study is to come to a better understanding of behavioral pattern of Green Tiger Prawn in its exploited phase after recruitment to the fishery. In this study, the confirmation of the life cycle of P. semisulcatus, to the general life pattern of Penaeidae shrimps was observed. Of the peculiarities of this pattern are the yearly bi-modal spawning and two corresponding peaks of recruitment. There exist two spring and autumn generations, which the major spawning in autumn produces the main recruitment in summer and the autumn generations stem from spring spawning. The spatial and temporal distribution of shrimp is highly variable by month and year. Depending on the year, higher shrimp densities are often found in early summer between Lavar and Rostami and/or Rostami to Bushehr and extend north and south in August. This result can be used in better design of sampling scheme for nursery studies. The main recruitment, which the fishery is depended upon, is in July to August and a second one occurs December-February. The timing and strength of both recruitments vary inter-annually. The proportion of prerecruits in southern area is always higher and the modes more prolonged than in northern area. The period of major recruitment starts earlier and lasts longer in the south than the north. A consistent pattern is not seen for the secondary recruitment, which, usually occurs in December-January. It is hypothesized that 1- the secondary recruitment might occur in Kuwait and/or Saudi Arabia waters, 2- insufficient number of spawners in spring or 3- high mortality in summer could cause the weakness of secondary recruitment. The spatial distribution of the mature female shrimps in spawning months indicates that the northern part of study area is an aggregation ground. It is also found that this aggregation grounds are close to two main fresh water sources (Helleh and Mond rivers), and these phenomena can be somehow related. The average length at 50% maturity varies inter- annually and is estimated to be 15.3 Cm. Length-frequency distribution of shrimps by sex reveals 1 to 3 modes depending on the month and year. In southern part a more complicated and less consistent pattern of recruitment and growth between years was observed. There is multiple or/and continuous recruitment especially during summer months. The von Bertalanffy growth parameters were estimated. The Findings are used to design new sampling schemes to cover the whole life cycle of this species enabling one to explain the variations in their response to the environment and fishery. The results of this study, lead us in building appropriate assessment and management models