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Published on: July 30, 2019
Bayesian Growth Modeling and Length-Based Indicators: Stock Assessment of Nile Tilapia (Oreochromis niloticus) in
Manar Abdellatif1, Richard Kindong1,2,3,4,5, Khaled Y AbouelFadl6
1College of Marine Living Resource Sciences and Management, Shanghai Ocean University, Shanghai 201306, China.
Abstract:
The present study incorporates age- and length-based methods to estimate the stock status of Nile tilapia (Oreochromis niloticus) in the inland fisheries of Lake Nasser, Egypt. In 2021, a total of 570 specimens were sampled to determine the length-weight relationships, condition factor, maturity schedules, age structure and growth parameters. The age estimations were quite accurate, suggesting a lifespan of 5 years. Females attained 50% maturity at a length of 27.85 cm and age of 2.30 years, while males attained maturity at 29.93 cm and 2.45 years. The von Bertalanffy model best described growth parameters using the Bayesian approach. Length-based reference points produced from aLBI indicate a close association between length at initial maturity (Lmat = 29.3 cm) and optimal harvest length (Lopt = 30.8 cm). The Froese indicators indicate that all the proportions of mature fish (Pmat = 44.8%), fish of optimum size (Popt = 35.6%), and big spawners (Pmega = 18.1%) were below sustainability targets. The results indicate that non-selective fishing gear is responsible for growth and recruitment overfishing by harvesting fish at, or below, maturity. The integrated Bayesian-aLBI approach offers a rigors and transparent assessment for inland fisheries with limited data and support for size-based management actions to rebuild the Nile tilapia stock in Lake Nasser.
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