The life cycle of green tiger prawn in the northern part of the Iranian water, Persian Gulf Phase 1: the identification of migration route and determination of the spawning areas and nursery grounds
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AbstractShrimp fisheries in the Persian Gulf have a long history. Since 1960 trawl fishery for Penaeid shrimp developed in the middle part of the northern coasts of the Persian Gulf (Bushehr waters). From 1998 to 2004 landing of shrimp have fluctuated between 480t and 2700t per year. The major species of penaeid shrimp (more than 80 percent) in the Persian Gulf and Bushehr waters is Penaeus semisulcatus. More than 2000 vessels and 33000 fishermen in Bushehr area were involving of shrimp catch (August and September) in study area in the recent decade. This species has an economical important role in the region. The present study was carried out in Bushehr coastal waters from 2003-2005. This study are described the bio-dynamic and life history of Penaeus semisulcatus in Bushehr area. Monthly samples of shrimp were collected by R/V LavarII from January 2003 to March 2004 for 15 months in 50 fixed stations. The carapace length frequency data were used to estimate the growth, mortality and exploitation rates by FiSAT program for males and females. The Von Bertalanffy growth parameters were estimated as K = 1.6 Year-1 and 2.2 Year-1 and L = 38mm and 50.4mm for male and female respectively. The results of mortality rates for males are Z = 6.4 per year F=4.3 per year and M = 2.11 per year. These results for female are Z = 8.2 per year, F=5.8 per year and M 2.41 per year. The exploitation rates for male and female are E=0.67 and E = 0.70 respectively. Relatively high values of total mortalities and exploitation rates were obtained which indicate that this species is overexploited. The maximum age was calculated 15 months for females and 18 months for males. Gonad maturity results were shown, the major spawning periods of green tiger prawn in the study area is in winter and early of spring and also there is a minor peak in autumn. Therefore two peaks of spawning were happened during this study. These periods are the main rainy seasons in the Bushehr area. The size at 50 percent mature (L50%) is 40.6mm and less than 5% of females were smaller than 24mm CL. Mature shrimps were aggregated in 20-30m depth of middle and southern part of study area. Imam Hassan, Genaveh and Helleh areas were the most important spawning grounds in Bushehr waters. The sex ration (male/female) of 0.84 was found during study period. This ratio was calculated in different months and the number of females were increased in spawning months. The number of 2571 shrimp were tagged and released by a green color polyethylene steamer tag during 15 months of survey and also before shrimping season (June and July) in 2005. The recaptures were done in two shrimp seasons in August and September 2004 and 2005 and 68 tagged shrimp recaptured that 4 recaptures were omitted due to inconsistencies information. Maximum recapture depths were 16-20m and 26-30m for males and females respectively. The majority of shrimp had a speeds of less than 2 Km/day, but maximum speed was recorded 3-4 Km/day in males and 2 Km/day in females. Only 10 percent of shrimp moved more than 50Km in study area and majority of shrimps, about 70 percent, were recaptured within 20Km of released area. The maximum recorded distance was 127Km after 95 days liberty in a female shrimp, but another female shrimp had only 20Km movement after 381 days and it was the maximum time between release and recaptured date. Tagged shrimp mostly moved to the northern part (Bahrekan area) of study area and recaptured shrimps pattern described stronger movement to the deeper waters. In the shallow waters of study area, sampling of juveniles of Penaeus semisulcatus was carried out from July 2003 to March 2005. The survey was done after spawning months of this species and sampling were carried out in July, November and December 2003 and January, February, April, June, July 2004 and February and March 2005. Some stations in less than 10m depths were trawled by a small boat, equipped with a small beam trawl and the prawns (P. semisulcatus) less than 15mm carapace length were collected as juvenile. In this study 748 individuals shrimp were collected during study period. These juveniles were observed in July and November 2003 and April and June 2004. The carapace length of juveniles ranged from 3mm to 15mm and minimum of mean of carapace length were 4.5mm in November and maximum 9.6mm in July. The juveniles were observed around southern part (Mottaf) and middle part (Helaileh) of vegetated sites. A few juveniles were observed in non-vegetated areas. In the nursery grounds 47% of marine organisms were included other species that Sparidae, Platycephalidae, crabs, shells and other penaeid shrimp species such as Metapenaeus af inis and M. stebbingi were observed in nursery ground of green tiger prawn. Very few juveniles were caught during the colder months and seasonal abundance of juveniles was observed in the warmer months. Present study was shown that mature shrimp are dominant from December till March and juvenile stages were mostly observed in April to July. Spawning was occurred through the year, with two peaks minor in autumn and major in winter and spring. Fishing activity should be controlled in spawning and nursery ground of shrimp.
Publisher or UniversityIranian Fisheries Science Research Institute
Series : Nr85.662;