Opening and closure of fishing season and estimation of biomass for green tiger prawn in Bushehr waters
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AbstractFrom 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
Publisher or UniversityIranian Fisheries Science Research Institute
Series : Nr83.147;