An investigation of some biological aspects of three species: tiger toothed croaker, Otolithes ruber, Javelin grunter, Pomadasys kaakan and black pomfret, Parastromateus niger in the Oman Sea for optimizing fishing season

Abstract

During the years 1382-83, some biological aspects of three species Tiger-toothed Croaker, Otolithes ruber, Javelin grunter, Pomadasys kaakan, Black Pomfret, Parastromateus niger, have been investigated in the Oman Sea along Sistan-O-Baluchistan province. Based on the frequency of developed maturity stages (IV, V), a prologed spawning activity extending from August to March was determined for O.ruber, and the Gonadosomatic Index (GSI) suggests two peaks:the minor one in October and the major one in March-April. Comparison of Hepatosomatic Index (HI) and Condition factor (Kn) with the peak spawning indicated a reverse relationship. According to length at first maturity (Lm50%= 40cm) and exploitation of fish at length 42cm above, the stretched optimum mesh size of nets was calculated to be 100mm. On analysis of stomach food item, fish group dominated (80%), which of them Anchovy accounted for 40% of the total frequency. Comparison of mean length between the years 1374-75 and 1382-83 showed 4cm in decrees. Population dynamics parameters were determined through length based modals and the exploitation rate was estimated to be E=0.6, suggesting high level exploitation. The usal streched mesh size of nets(constructed from multifilament webbing) for capturing O.ruber were less than the proposed optimum mesh size of nets, indicating 78% of the total landings were smaller than Lm50%. Total landings in 1381 have increased up to 15% when compared to those of the year 1376. Despite the decrease of total efforts (Panel.day) by 37%, the mean value CPUE has increased up to 82%. Regarding Pomadasys kaakan species, a year-round spawning activity has been observed, with two peaks: A major one in April and an aminor one in September. As those of O.ruber species, there was an inverse relationship between HI and Kn with the peak spawning activity. Based on the length at first maturity (Lm50% = 44cm) and capturing fish of the length at 46cm and above, the stretched optimum mesh size of nets was calculated to be 149.6mm. According to analysis of stomach contents, fish group accounted for 35% of the groups studied, which of them , Largehead hairtail, Trichiurus lepturus linnaeus, constituted 52% of the total frequency. In addition to estimation of population dynamics, the exploitation rate was estimated to be E= 0.49. Majority of the species catch was made by mesh size of nets used for O.ruber of which 133mm mesh size accounted for the level (30%). Information on length distribution showed that 60% of the total fish landed was below Lm50%. Total landings in 1381 decreased to 10% in comparison to 1376.Total fishing efforts and CPUE also decreased to 33% and 24% respectively. For parastromateus Niger, There was a long period spawning activity from March to December, with two peaks: A major one in August and a minor one in March. According to Lm50% (39cm) and catching of fish 39cm above, the stretched optimum mesh size of nets was calculated as 167.7mm. Based on stomach contents, ring-shaped worms and larval shrimp equally made 29% of the total frequency showing the highest contribution. Comparison of mean length indicated 3cm in decrease in 1382-83 when compared to 1374-75. Population dynamics parameters were estimated and the exploitation rate was estimated to be E = 0.54. The usual stretched mesh size of nets for P. niger was 146mm and 81% of the total fish landed were smaller than Lm50%.In 1381,total catch of the species increased four and a half-fold in comparison to 1376, while total efforts decreased up to 28% and CPUE increased two and a half-fold