فهرست مطالب yassein a.a. osman

An increased understanding of fisheries target species population dynamics is a key requirement for successful management. Age, growth, and mortality of Indian mackerel, Rastrelliger kanagurta were estimated based on samples collected from commercial purse seine fishery in the Egyptian Red Sea between October 2019 and September 2020. The age estimates were based on two readers to increase the accuracy of results. The age estimates, in the period of study, were observed at a maximum age for both sexes at 4 years old and the most sampled occurrences in the second years (2 years old). The von Bertalanffy growth function was estimated for males at L∞= 343.83-0.447 (t+0.474); for females at L∞= 367.37-0.357 (t+0.767) and combined at L∞= 353.78-0.406 (t+0.595) . The mortality rate was determined at 1.35, 1.32 and 1.37 year-1 and exploitation ratio at 0.417, 0.511 and 0.492 year-1 for males, females and combined receptively. The length at first maturity (L50) was estimated at 206.9, 208.26 and 207.48mm for males, females and combined receptively. The updated estimates of these biological parameters, by this study, indicate that R. kanagurta population is more vulnerable to fisheries exploitation than before.

Otolith shape and morphology are used to identify fish species and population stocks. The aim of this study was to distinguish the Lethrinus lentjan (Lacepède, 1802) and L. microdon (Valenciennes, 1830) (family: Lethrinidae) using otolith shape. The analyses apply the ShapeR package in R which enables to extract the outline and otolith morphology from images and for statistical examining of individual variation. Otoliths of 165 individuals from the two Lethrinus species were collected during 2019 and 2020. The wavelet levels were examined by using 6 wavelets to collect 63 coefficients. The regression between width and fish length were b = -0.03 (t = 2.6, P = 0.01) for L. lentjan and was significantly different (t = 2.120, P = 0.036) for L. microdon (b = 0.018).