Growth, Mortality, Yield Per Recruit and Management of Siganus rivulatus Stock from the Suez Canal, Egypt

Abstract

Siganus rivulatus is considered one of the most successful Lessepsian migrant fish, yet the scarce of studies about its population structure in new habitats of the Suez Canal is clearly realized. In the present study, the yield per recruit of S. rivulatus was estimated in Suez Canal based on investigation of growth parameters, mortality coefficients and exploitation rate for 581 individuals collected seasonally from Ismailia during the period from autumn 2017 to summer 2018. Otolith was used for aging and estimation of the growth rates. Four years was the maximum attained age. The von Bertalanffy growth parameters were L∞= 25.356 cm, K= 0.288 y-1 andt0= -0.81 y. Total mortality coefficient (Z) was 1.57 y-1, natural mortality (M)= 0.573 y-1 and fishing mortality (F)= 1. 002 y-1. The length at the first capture (Lc= 12.838 cm) was found to be smaller than the lengths of first maturation (Lm= 14.5 and 15.15 cm for male and female, respectively). This may cause a great reduction in the stock due to harvesting small pre-spawning fish. Hence, the exploitation level was estimated recording a value of (E)= 0.636 y-1, which indicated that the stock of Siganus rivulatus in the Suez Canal is currently overexploited. Therefore, conservation of this stock is a must, which can be achieved by increasing the allowable mesh size to give a chance to each individual to reproduce at least once and reducing the exploitation rate from 0.636 to 0.355 y-1 to maintain a sufficient (50%) of the spawning stock biomass.