English abstract
Longnose trevally (Carangoides chrysophrys) samples were collected on
monthly basis between April 2005 and September 2006 from two landing sites (Allkbe and Raysot) in the Arabian Sea to study the biology and assess the fishery of this species. Morphometric measurements for each fish include total length (TL), fork length (FL), standard length (SL) and depth of the fish length was taken and total body weight (TW). The fish was then dissected to determine the sex macroscopically and to record the gonad weight (GW), liver weight (LW) and the stomach weight (SW). Otolith was used for ageing and the marginal zone analysis was used for validation. Total mortality estimated from age converted catch curve method. Alagaraja (1984) longevity equation was used to choose the best estimate of different natural mortality equations. The stock was assessed using yield and spawning biomass per recruit analysis. No significant differences between the male and female in morphometrics relationships except for the depth-total length relationship. Analysis of variance found significant length-weight relationships for all maturity groups and sex. The t-test for b value showed that C. chrysophrys displays negative allometric growth for both sex and combined. Analysis of covariance showed no significant difference in length - weight relationship between sex for different maturity groups and combine. The average condition factors (Kn) versus length decreases with an increase in size and males have higher average condition factors than females on size and monthly base. The average condition factor (Kn) fluctuate around the year and can't related to the spawning season. One opaque band and one hyaline band were deposited in one year and the opaque band lead down between December and March. The otolith weight age relationships were not significantly different between the sexes. Otolith weight correlated about 0.69 to age subscript for both sexes. sixteen years is the maximum age recorded for both sexes. No significant difference was detected in the sex ratio of the pooled age groups. ARSS analysis showed that the von Bertalanffy growth models for males and females were not highly significantly different suggesting the use of pooled equation of both sexes Lt = 73.2 (1 - e-0.25 (t+1.21), The sex ratios were significantly difference (df = 1, x = 6.5 in month and length; 6.72 maturity stage, a = 0.05). One peak for the gonadosomatic index (GSI) started from September and ended in February. Liversomatic index (LSI) and coefficient of condition (K) were constant around the year. The female mature significantly earlier than male, at 42.08 and 46.90cm total length and at age of 4.1 and 4.7 years, for female and male respectively. Four types of ova were observed immature (6–8md), maturing (18–20md), mature (27 - 29md) and ripe (39 - 41md).
Alagaraja (1984) natural mortality equation gave the best estimate of longevity and hence chosen to present the natural mortality rate. Natural mortality (M) equal to 0.288yr and the total mortality (Z) equal to 0.3854 yr. Length at 50% capture of longnose trevally found at total length of 38.21cm and age of 4yr. The yield and spawning biomass per recruit analysis indicate that the current fishing mortality rate (Fcurr) smaller than the maximum fishing effort (Fmax) suggest that it is at an optimum level and should be maintained. However, any increase in the fishing effort may lead to
