ALBERT

Description: 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.

Description: Iranian Fisheries Science Research Institute

Description: Published

Description: From December 1998 to March 2001, (28 month) a survey in Iran waters were completed. Each month, 50 stations in four depth stratums that is, below 10 m, 10-20 m, 20-30 m and above 30 meters from Bahrekan to dayyer were trawled. Some Biological parameters such as sex stages, sex ratio, total length, species composition and some environmental factors such as water temperature, air temperature, salinity, soluble oxygen, acidity of seawater were measured. In this survey, the effects of environmental factors on shrimp behavior and landings were assessed. According to analysis, spawning season extends from January to May. Maximum percentages of mature stage (4th stage of maturity) were observed to be 53.4% in April 1999 and 47.6% in May 2000. Water temperature and salinity were 23.1 centigrade and 37.2 PPT and 21~'C and 38.7 PPT in spawning seasons of 1999 and 2000 respectively. The catch composition of shrimp in fishing season (July to September) for the years 1999 and 2000 has been observed to be 60.2% and 66.4% for 〈i〉Penaeus semisulcatus〈/i〉, 37.1% and 30.4% for 〈i〉Metapenaeus affinis〈/i〉, and 2.5% and 2.8% for parapenaeopsis stylifera respectively. Maximum catch per unit effort (CPUE) in fishing season of 1999 and 2000 were observed to be in depth ranges of lower than 10 meters and 10-20 meters respectively. Analysis of length frequency data shows that the first schools of juvenile tiger shrimps appear in middle region of Persian Gulf from May to June (in low density). In later months (July to August), the schools of juvenile shrimps gradually appear in northern areas. After closure of shrimp fishery (late September) the density of adult shrimps in northern area increase. These shrimps have an average length of more than 15 Cm and are sexually matured. Analysis of sex ratio shows that in fishing season, the number of Male and females are almost equal (sex ratio=1). In Nov. and Sep., the number of females increases (decrease of sex ratio). In spawning season the number of females decrease (increase in sex ratio) but approaching to the coming fishing season the sex ratio tends to become 1 due to recruitment. Observations show that during fishing season the sperm sacs of Male gradually evolve so that at the end of fishing season, the sperm sacs are seen as two white tissue under the last pairs of Pereopods. In other observations, some of sperm had come out from steam of pereopods and cleave to legs of shrimp (both males and females). These observations show that shrimp schools come to fishing grounds for copulation. The stock-recruitment relation has not been proved to be correct and environmental factors has had more effect on size of shrimp stock. A linear relationship with a high correlation coefficient of r〈super〉2〈/super〉=0.9 between prefishing season CPUE and the landings of the same year was established. (Landing =56 CPUE+286). Finally, it is shown that, lower water temperature in spawning season results in better spawning and thus higher yield

Description: Iranian Fisheries Science Research Institute

Description: Published

Description: 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.