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Population parameters of Whipfin silver-biddy (Gerres filamentosus) and Longtail silverbiddy (Gerres longirostris) were studied from January to December 2006 in three creeks (Markazi, Khalasi and Gabrik) of Hara protected area in Jask, Oman Sea. All fishes were sampled by boat trawl and beach seine. Growth parameters were determined using the monthly length–frequency parameters. The Mean total length was calculated at 6.2 and 5.4cm for Whipfin silver-biddy and Longtail silver-biddy. The values of L∞ and K for Whipfin silver-biddy were 16.8cm and 0.99 yr-1 and for Longtail silver-biddy, these were 15cm and 0.77 yr-1, respectively. The value of to was calculated at -0.12 year for both species. The longevity was estimated to be 3 years for Whipfin silver-biddy and 3.8 years for Longtail silver-biddy. The length-weight relationship were determined as W= 0.0088 L3.21 and W= 0.0087L 3.18 for Whipfin silver-biddy and Longtail silver-biddy, respectively. Results showed the fish were in their juvenile stage which emphasized the supporting roles of creeks for Gerridae as nursery ground. * Corresponding author

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In this investigation, the amounts of organic matter, types of sediment and distribution of macrobenthic species in the Boojagh Marine National Park (BMNP) were studied. Sampling was conducted in six transects perpendicular to the beach using a Van Veen grab sampler using cross section of 20 cm with five replications. Samples were collected in five seasons (from summer 2015 to summer 2016). Each transect include three stations at various depths of 1, 5 and 10 meters. Samples were washed and fixed in formalin. Then, they were transferred to a laboratory for sorting and identification of different groups of macrobenthic taxons. The identified species were as follows; Cerastoderma glaucum, Mytilaster lineatus, Pyrgula grimmi, Anisus kolesnikovi, Stenogammarus carusui, Paraniphargoides motasi, Onisimus caspius, Pterocuma pectinatum, Pterocuma sowinskyi, Pseudocuma (Stenocuma) gracile, Naiss sp., Hypania invalida, Manayunkia caspica, Streblospio gynobranchiata, Hediste diversicolor and Amphibalanus improvisus. Evaluation of sediment composition indicated that the highest proportions belonged to sand with an average amount of 89/25%, whereas the lowest proportions belonged to clay with an average amount of 0/26%. with highly significant difference among sand identified with other particles (p<0/01). The average percentage of organic matter in the summer 2015 in the fourth transect at the depth of five meters was significantly lower than that of the others (p<0/01). The highest density of macrobenthos was at the depth of 10 meters. Macrobenthos density was the highest in the summer 2015 and was the lowest in the spring 2016 as compared to the other seasons.