Abstract
The structure of a fish population is determined by the equilibrium between growth, recruitment and total mortality. But, there is paucity of information on the growth and mortality of Mormyrus rume in Nigeria. Therefore this study is needful to determine its population parameters, with a view of evolving management strategies for its sustainable exploitation. Estimates of population parameters of Mormyrus rume were obtained from length-frequency data of 836 individuals collected monthly for a period of 24 months from January 2017 to December 2018. The estimated growth parameters were: asymptotic length (L∞) was 100.8cm; growth coefficient (K) was 0.62/year; growth performance (Ɵ) was 3.8; length at maturity (Lm) was 52.57cm; reproductive load (Lm/L∞) was 0.52 and optimum length (Lopt) was 65.10cm. Likewise, natural, fishing and total mortalities were 0.93, 1.46 and 2.39 respectively. The values of exploitation rate (0.61) and ratio of total mortality and growth coefficient (3.85) showed that Mormyrus rume is most exploited in Ikere-gorge. Therefore, appropriate fishing regulations should be enforced to regulate fishing gears and mesh size that will fish Mormyrus rume at sustainable level.
 Keywords: Recruitment, mortality, growth, exploitation, length
Highlights
Fishery management systems depend on regular stock assessments to determine stock status and to provide appropriate advice for management decision to achieve fishery and conservation objectives
The maximum length (Lmax) of M. rume observed in this study is consistent with the report of Olaosebikan and Raji (2004) that adult M. rume can reach a maximum length of 100 cm
It was observed that the exploitation of M. rume in Ikere-gorge is not sustainable
Summary
Fishery management systems depend on regular stock assessments to determine stock status and to provide appropriate advice for management decision to achieve fishery and conservation objectives. Stock assessment involve provision of information on recruitment, mortality, migration, fishery monitoring, and resource surveys for estimating stock size and harvest rate relative to sustainable reference points. It compares the present and expected fish abundance at a particular period of time to determine the exploitation level of the stock whether the stock is overexploited or not; it tells us if a catch level will maintain or change the abundance of the stock. Stock assessment is usually carried out by applying statistical and mathematical models to make quantitative predictions about the reactions of fish populations to alternative management choices (Bonfil, 2005; Cadrin and Dickey-Collas, 2015). The structure of a fish population is determined by the equilibrium between growth, recruitment and total mortality
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