family belonidae from the suez canal, egypt: age, growth, mortality, exploitation rate and reproductive biology

Abstract

This is the first attempt to study the biological characteristics and basic population parameters of two important Belonidae species, Tylosurus acus and Tylosurus crocodilus from the Suez Canal. The length– weight relationship was estimated as W = 0.0005TL3.26 for T. acus and W = 0.0007TL3.21 for T. crocodilus. The growth parameters of T. acus were computed as L∞ = 79.85 cm, k = 0.44 year–1, t0 = –0.58 years, while the annual total, natural and fishing mortality were 1.70, 0.72 and 0.98 respectively with an exploitation rate of 0.58. While in T. crocodilus the VBGPs were L∞ = 113.0 cm, k = 0.30 year–1, t0 = –0.46 years, the annual total, natural and fishing mortality were 1.27, 0.51 and 0.76 respectively with an exploitation rate of 0.60. The female's length at first maturity of T. acus was estimated to be 47.3 cm and 51.7 cm for T. crocodilus. Monthly variations in Gonado-somatic index revealed that the spawning season of the two species takes place in spring. Results of exploitation rate indicated that the T. acus and T. crocodilus are fully exploited. Keywords: Tylosurus acus, Tylosurus crocodilus, Population dynamics, Length at maturity, Spawning period