A survey on some biological aspects of spiny lobster Panulirus homarus for optimizing fishing season in Sistan - o – Baluchestan province

Research project was conducted on some biological aspects of lobster in Oman Sea in the years1385-86. During the project some parameters such as length distribution, spawning peak, length (Carapace) at first maturity, the length at which 50% of the lobsters were found to be mature sexually, sex ratio, relative frequency index and population dynamics parameters were examined. Quantitative factors and catch composition of lobster including the amount of catch in terms of weight and number of ovigerous-female, under-sized specimens and so were compared by monthly. According to the results of present study caught specimens were male with carapace length of 22 and 110 mm respectively. The smallest ovigerous female was taken as 46mm CL when length at first maturity was estimated to be 69-70mm. the male: female ratio was 0.7: 1.3 for the whole year. A closed fishing season for the species is proposed during spring and September and October in Oman Sea. A large amount of the catches for the all sampling months came from the under-sized specimens, consist of 50 to 85% of the total catch. Therefore, presence of these small length groups have direct effects on time of closing season. Population dynamics parameters were calculated as follows: K=0.57 year, L∞= 103mm and Ǿ = 8.69. Total mortality (Z), natural mortality (M) and fishing mortality (F) coefficients were calculated as 2.73, 0.87 and 1.86, respectively. Exploitation ratio for the whole population was 0.681, indicating an overexploitation of the species. Based on the available data, the recruitment pattern for lobster was obtained for two season including spring (major) and autumn (minor). Catch per unite effort (CPUE) was calculated as 0.908 kg/Cage/day which was higher in comparison with two other areas including Ramin and Chabahar. Examination of CPUE for a 10-year period showed a decreased trend and the reduction for the year 1386 was about 30% when compared to the data from the year 1375. Moreover, the mean length during 1369-70 to 1385-86 (present study) decreased for the three areas including Pozm, Ramin and Chabahar, so that the carapas length decreased up to 10 mm in length. This sudden decrease in mean length during the 10-year period should be considered as a serious precariousness for sustainable exploitation of lobster in Oman Sea along Sistan and Baluchistan province.