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

Abstract

The age and growth of the Olive tail <i>Rogadius asper</i> 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±0.03year^-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 <i>R. asper</i> 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 <i>R. asper</i> 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.