Austin Wehye

The study evaluated some population parameters of Galeoides decadactylus within Liberia's coastal waters. A total of 1618 samples were collected from eight coastal counties of Liberia from April, 2013 to September, 2013. Total length of individual fish samples was measured and analyzed using FiSAT II software. Von Bertalanffy parameters were estimated at asymptotic length (L∞) = 54.08 cm, growth rate (K) = 0.19 per year, the longevity (Tmax) = 15.8 years, theoretical age at birth (t0) = −0.75 years and growth performance index (Φ′) = 2.745. The length first capture (Lc50 = 9.41 cm) was lower than the length at first maturity (Lm50 = 13.8 cm). Mortality parameters were calculated as total mortality rate (Z) = 0.91 per year, natural mortality rate (M) = 0.49 per year and fishing mortality rate (F) = 0.42 per year. The exploitation rate (E) and maximum exploitation rate (Emax) were 0.46 and 0.45 respectively. Galeoides decadactylus fishery in Liberian coastal waters was found to be experiencing unsustainable exploitation as well as growth overfishing. Thus, to avert the consequences of growth overfishing, sustainable fisheries measures including monitoring of fishing efforts and increase in mesh size should be implemented and enforced.

The study evaluated the population structure and biology of two sciaenids within Liberia's coastal waters. A total of 177 and 152 samples of P. senegalensis and P. typus respectively were collected from two landing sites in two coastal counties of Liberia from July, 2016 to December, 2016. Each individual fish specimens was measured for standard length, weight and analysed using FiSAT II software and Excel Analysis Toolpak. Spawning periods of the two fish species were determined following the monthly variation of the mean gonadosomatic index. Fish condition factor for both genders of P. senegalensis and P. typus was influenced by the sea surface temperature (SST). Based on the monthly GSI's variation, the two species spawned doing the hydrological seasons. The length-weight relationship of both species shows negative allometric growth. There were dominants of males to females for the two assessed species. From the results urgent management interventions in form of close seasons are needed to safeguard these commercially important fish species from possible stress in the future to avert natural mortality dominants.

The phytoplankton composition and the physic-chemical parameters of the downstream , mid-stream and upper-stream of Agenebode lower river Niger was investigated between April and October, 2015. A total of 80 phytoplankton species belonging to four divisions; Bacillariophyta, Chlorophyta, Cyanophyta and Euglenophyta which includes 34 genera, 10 orders and 17 families were observed. All the species of Bacillariophyta observed were pennate forms. Only Surirella elegans was observed in the three areas while Aulacoseira granulata, was observed in upper stream and Spirogyra dubia in the downstream of the river. The taxa were dominated qualitatively by green algae (desmids). The mid-stream accounted for most of the desmids encountered. Generally the division Chlorophyta had the highest percentage composition (45%), followed by Bacillariophyta (32.5%), Euglenophyta (15%) and Cyanophyta (7.5%). The physico-chemical parameters studied showed that temperature fluctuated between a mean of 27.5 ° C to 31.75 °C. The pH values of the three areas had a mean range of 6.39 to 7.20; the DO for all the studied area were within 4mg/L to 10mg/L but there was variation in the mean conductivity values (DNS, 75.3μScm-1 ; MDS, 67.58μScm-1 ; UPS, 50μScm-1).

This study examined some aspects of population dynamics of 1776 specimen of S. maderensis (Lowe, 1988) from Liberian coastal waters, from April 2013 to September 2013 (total of six months) using the FiSAT II for analysis. From the results, the growth was assumed to follow the von Bertalanffy growth function with asymptotic length (L∞) and the growth coefficient (K) estimated at 44.63 cm total length and 0.38 year-1 respectively. The growth performance index, longevity and the theoretical age at birth (t 0) were estimated as 2.88, 7.51 years and-0.387 year-1 respectively. The length at first capture (L c50 =13.99 cm) was lower than the length at first maturity (L m50 =29.75 cm), an indication that most of the harvested stock were juveniles. Instantaneous rate of total mortality, natural mortality and fishing mortality were estimated as 1.24 year-1 , 0.81 year-1 and 0.43 year-1 respectively. The current exploitation rate (E) and maximum exploitation rate (E max) were calculated as 0.34 and 0.36 respectively. Results from the study indicated that the exploitation of S. maderensis is at the maximum sustainable yield coupled with the presence of growth overfishing and intense fishing pressure. Therefore, urgent management actions including increasing fishing gears mesh size and regulating fishing effort is needed to protect the S. maderensis stock.

This research article seeks to provide information about some aspects of population dynamics of P. typus in the Liberia coastal waters for strategic management and sustainability. A total of 1,822 specimens of P. typus were collected for six months from April to September 2013. The length frequency data was analyzed using FiSAT II and yield software. The asymptotic length, growth rate, growth performance index and the theoretical age at birth were estimated as: L∞ = 84 cm SL, K = 0.04 yr –1 , ø = 2.451 and to =-0.276 yr –1 respectively, with the maximum age (tmax) at 74.75 years. Total instantaneous mortality rate (Z), natural mortality rate (M) and fishing mortality rate (F) were 0.26 yr –1 , 0.16 yr –1 and 0.10 yr –1. Exploitation rate (Ecurrent) and maximum exploitation rate (Emax) were estimated as 0.40 and 0.671 respectively. Growth overfishing existed in P. typus fishery, length at first maturity (Lm50= 56 cm) was higher than length at first capture (Lc50= 28.48 cm). The recruitment pattern was continuous with two major recruitment pulses. Visual Population Analysis results showed that mid-length 45 cm experienced the highest fishing mortality. The fishing regime of P. typus fell in the eumetric stage based on the quadrant rule. Maximum Sustainable Yield (MSY) was 6,621.54 tonnes. From the results growth overfishing was identified within P. typus fishery within Liberian waters dovetailed with absence of recruitment overfishing. P. typus was underexploited, requiring management interventions to increase exploitation sustainably.