Age, growth and mortality characteristics of the Thumbprint Emperor (Lethrinus harak) in Zanzibar

Abstract

The growth parameters of Lethrinus harak were studied in Zanzibar water from 308 samples collected between June 2019 to May 2020 at Unguja Ukuu and Mkokotoni landing sites. The annulus count indicated that the majority of fishes captured were of three and four years old and very few were five, six, and seven years of age with a mean length of 17.69 cm, 21.04 cm, 24.18 cm, 25.86 cm, and 28.15, respectively. The number of rings was counted on the whole otolith and the growth rings were revealed to be formed annually, with the opaque margins generated from December to February and the hyaline ones during the rest of the year. The growth parameters were estimated as L_∞=34.22cm, K=0.25 year-1, and t₀=0.00. The total mortality (Z) was estimated as 0.68 year^-1 and natural mortality (M) was estimated using Pauly's equation, as 0.65 per year^-1 and fishing mortality (F) was 0.03 year^-1, which gives an exploitation rate (E) of 0.04 year^-1. Although these values indicate the species to be underexploited, the absence of older individuals 15 years and smaller below three years might have affected our findings.