INTEGRATED STOCK ASSESSMENT OF GREY MULLET (MUGIL CEPHALUS) IN THE CROSS RIVER ESTUARY, NIGERIA

Abstract

The grey mullet (Mugil cephalus) supports vital artisanal fisheries in West African estuaries, but sustainable management is hindered by limited quantitative stock data. This study aimed to assess growth, mortality, recruitment, and fishing pressure on M. cephalus in Nigeria’s Cross River Estuary using length-frequency data collected monthly over two years (2023–2024). Von Bertalanffy growth parameters estimated an asymptotic length of 36.75 cm and a growth coefficient of 0.95 year-1. Total mortality was 4.10 year-1, with natural mortality at 1.66 year-1, yielding a fishing mortality of 2.44 year-1 and an exploitation rate of 0.60, exceeding sustainable limits. Recruitment analysis revealed year-round recruitment with a distinct peak in May. Gillnet selectivity was low, allowing capture of juveniles and adults. Virtual population analysis confirmed fishing mortality well above natural mortality across size classes, with exploitation rates surpassing biological reference points (E10 = 0.355, Emax = 0.421). The evidence indicates growth overfishing and emphasizes urgent management interventions such as gear modification and seasonal closures. These results provide crucial insights for sustaining tropical estuarine mullet fisheries.