Aspects of Population Dynamics of Pagrus Caeruleostictus Collected From the Continental Shelf of Sierra Leone and the Implications for Management

Komba Jossie Konoyima,Lahai Duramany Seisay

doi:10.3329/ralf.v7i3.51371

Abstract

The study evaluated aspects of population dynamics of Pagruscaeruleostictus and the implications for management in Sierra Leone, needed to support efficient management plans of its fishery. 12, 729 specimens of Pagruscaeruleostictus were collected off Sierra Leone from January-November, 2016 using randomized sampling techniques on-board demersal trawler. Analysis of population dynamics employed methods fitted in FiSAT II software using pooled length-frequencies. Estimated growth parameters were asymptotic length (L∞ = 34.48cm) and weight (W∞ = 4693.6g), growth rate (K = 0.29yr-1), growth performance index (ɸ = 2.54), growth exponent (b = 3.09), theoretical age (to = -0.8years) and life-span (tmax = 9.50years). The instantaneous fishing mortality rate (F = 0.40yr-1) climaxed the optimum fishing mortality rate (Fopt = 0.30yr-1) and slightly below the limiting fishing mortality (Flimit = 0.51yr-1) whereas natural mortality rate (M) gave 0.76yr-1. Besides, the estimated current exploitation rate (Ecurrent) exceeded the estimated sustainable level of exploitation (E50 = 0.39yr-1) but below the estimated maximum allowable exploitation point (Emax = 1.10yr-1). Further, the length (Lm50 = 23.00cm) and age (tm50 = 4.60years) at first maturity climaxed the length and age at first capture (Lc50 = 21.64cm, tc50 = 3.8years,), length and age at first recruitment (Lr = 13.00cm, tr = 2.4years). Results portrayed slow and isometric growth, median life-span and high survival of a continuously recruited spawning stock of Pagruscaeruleostictus. Also, the stock suffered growth overfishing, moderate fishing pressure and overexploition, implying the need for management to recalibrate measures for rational exploitation. Res. Agric., Livest. Fish.7(3): 517-531, December 2020

Highlights

Pagrus caeruleostictus (Valenciennes 1830) commonly called the “Blue Spotted Seabream” is a demersal species of the Sparidae family that occurs in most part of the Mediterranean Sea (Bauchot and Hureau, 1986; Fischer et al, 1987) at depth ranging from 30m to 200m (Bauchot and Hureau, 1986; Schneider, 1990) with more frequent occurrences in the Eastern Atlantic (Bauchot and Hureau, 1986)
Growth Parameters The modified Powell-Wetherall plot (Figure 2) for Pagrus caeruleostictus gave a preliminary estimate of asymptotic length (L∞) and Z/K ratio as 34.48 cm and 4.65 respectively
The special von Bertalanffy growth function for growth in weight of Pagrus caeruleostictus was predicated : the Bhattacharya option for modal progression analysis (Figure 3) gave three modal length groups for the population of P. caeruleostictus of mean (±SD) lengths as 12.5 ±0.79cm, 21.12±2.29cm and 28.03±0.98cm with corresponding age groups of 2.40years, 4.10years and 6.60years, respectively

Summary

Introduction

Pagrus caeruleostictus (Valenciennes 1830) commonly called the “Blue Spotted Seabream” is a demersal species of the Sparidae family that occurs in most part of the Mediterranean Sea (Bauchot and Hureau, 1986; Fischer et al, 1987) at depth ranging from 30m to 200m (Bauchot and Hureau, 1986; Schneider, 1990) with more frequent occurrences in the Eastern Atlantic (Bauchot and Hureau, 1986). P. caeruleostictus constitutes one of Sierra Leone‟s economically important demersal fish species targeted by both artisanal and industrial fishery sectors (Showers, 1995; Sesay, 2014; Seto et al, 2015). The species contributed 1.77% at 0-30m, 26.30% at 31-50m, 17.70% at 51-100m and 41.10% at 101-200m depth zones of important demersal species in Sierra Leone (Sesay, 2014). Study of fish population dynamics provides insight of the status of stock including age and growth, mortality, exploitation rates, recruitment, vulnerability to capture, relative yield and relative biomass per recruit needed to formulate management measures most appropriate for sustainable exploitation of valuable stocks (Gheshlaghi et al, 2012; Amponsah et al, 2016; 2017; Asadollah et al, 2017; Wehye et al, 2017; Mehanna, 2018). The objective of the present study was to evaluate aspects of population dynamics of Pagrus caeruleostictus collected from the Continental Shelf of Sierra Leone and the implications for management. The study will be vital to future researchers owing to scarcity of published work in Sierra Leone and wide

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Results

Conclusion