Age, Growth and Demographic Structures of Thorny Flathead Rogadius asper, Cuvier, 1829 (Pieces: Platycephalidae) from the Coastal Waters of the Suez Gulf

摘要

The age and growth of the Olive tail Rogadius asper exploited by the demersal trawl fishery in the Gulf of Suez were investigated during the fishing season 2014/2015. Ageing was done by sagittal otoliths for a sample of 675 ranged from 9.2 to 25.9 cm in total length (TL) with mean of 17.4±2.95 cm. The sex ratio was skewed in favors of females (1.6:1), which tended to high in number and bigger in size than males. The maximum investigated age of females was 4 years and that of males was 3 years. The mean von Bertalanffy growth parameters for both sexes L∞=26.43±0.22cm and K=0.47±0.03 year~(-1) as estimated by four different methods. According to gender the growth was variable and significantly differed (P<0.05=0.002). Females attained a greater mean L∞ = 27.2±0.44cm than males L∞=24.0±0.26 cm and males displayed greater mean k value 0.53±0.02 year~(-1) than that of females K=0.43±0.01 year~(-1). Fish of age groups 1 and 2 years were dominated the age compositions of R. asper constituting 36.6% and 39.3 % respectively. The estimated value of total mortality, natural mortality and fishing mortality for the pooled data was: Z=1.51±0.25, 0.58±0.09 and 0.93±0.08 year~(-1) respectively. It was indicated that the fishing mortality was more than one third (37.6%) of the derived natural mortality and exploitation rate was 0.62, indicating that the species was heavily exploited. Although R. asper is not a target species of commercial fisheries, it suffers high exploitation as part of the by-catch for its suitable market price for insufficient income.