Length-weight relationship(LWR),condition factor(k)of the black chin tilapia,Sarotherodon melanotheron(Rüppel,1852)from Forcados River estuary Nigeria was investigated.The fish were collected monthly from fisherm...Length-weight relationship(LWR),condition factor(k)of the black chin tilapia,Sarotherodon melanotheron(Rüppel,1852)from Forcados River estuary Nigeria was investigated.The fish were collected monthly from fishermen for a period of 24 months(between April 2012 and March 2014).699 specimens of the fish species were collected.The Length-weight relationship(LWR)of the fish was evaluated using the equation:W=a L^(b) while the condition factor of the fish was determined using the equation;K=100W L^(b).The standard length of sampled S.melanotheron ranged from 4.15 to 18.92 cm,total length 6.01 and 22.5 cm while the weight ranged from 7.85-286.71 g.The b value 2.1299 was less than 3 indicating that the growth pattern of the fish was allometric.The correlation co-efficient(r)value for S.melanotheron was 0.7528.The condition factor for the combined sexes fluctuated monthly.The length-weight relationships and condition factor of S.melanotheron in Forcados river estuary indicated that the fish were above average condition.展开更多
This paper reviews the significant contribution of hydrologic continuity in the development, evolution and fate of the Niger Delta. Formed from the aggregation of sediments from a drainage catchment area of over 2 mil...This paper reviews the significant contribution of hydrologic continuity in the development, evolution and fate of the Niger Delta. Formed from the aggregation of sediments from a drainage catchment area of over 2 million km<sup>2</sup>, the Niger Delta has evolved into a prolific sedimentary basin with a dense network of rivers and creeks. The ecological system is in a fragile state with fresh and saline water ecosystems maintaining a dynamic equilibrium. Rainfall typically varies from 2500 - 4000 mm per year compared to average annual evaporation of about 1500 mm, resulting in net antecedent moisture. Over 70% of the rainfall occurs in 4 months between May and September, creating a potential for flooding. Water level varies from less than 1.5 m in the estuaries to about 8 m at the apex of the delta, with Nun River having a slightly higher elevation compared to Forcados River, implying that canals connecting both rivers at the same reach would experience water movements from Nun to Forcados River. Similarly, water level gradients vary across the stretch of the rivers from 8.6 to 9.5 × 10<sup>-5</sup> (cm/km) between Onitsha and Asamabiri, 7.5 to 7.7 × 10<sup>-5</sup> (cm/km) on the Forcados River downstream of Asamabiri, and from 7.4 to 7.6 × 10<sup>-5</sup> (cm/km) on the Nun River. At peak flood, about 23 × 10<sup>3</sup> m<sup>3</sup>/sec of runoff enters the Niger Delta. At the same time, about 16 × 10<sup>3</sup> m<sup>3</sup>/sec discharges from the estuaries into the ocean in a semi-diurnal tidal flow leaving a surplus that accumulates to cause flooding. The delta thus acts like a sponge, absorbing the shear amount of flow and releasing slowly stored water through at least twenty-one outlet estuaries into the Atlantic Ocean. The shear amount of discharge overwhelms the capacity of the network of distributaries and predisposes the delta to flooding. Assessment of the capacity of the rivers to evacuate pollutants showed that rivers to the west of Brass which are fed by Forcados River exhibited relatively stronger flux efficiencies prior to 1998 but are presently weaker compared to rivers fed by Nun. The rivers to the east between New Calabar and Imo Rivers exhibited very weak ebb tide asymmetry or net upstream flow largely because these rivers receive little or no freshwater influx from upstream sources. Flood and erosion are the major hydrological hazards in the region.展开更多
文摘Length-weight relationship(LWR),condition factor(k)of the black chin tilapia,Sarotherodon melanotheron(Rüppel,1852)from Forcados River estuary Nigeria was investigated.The fish were collected monthly from fishermen for a period of 24 months(between April 2012 and March 2014).699 specimens of the fish species were collected.The Length-weight relationship(LWR)of the fish was evaluated using the equation:W=a L^(b) while the condition factor of the fish was determined using the equation;K=100W L^(b).The standard length of sampled S.melanotheron ranged from 4.15 to 18.92 cm,total length 6.01 and 22.5 cm while the weight ranged from 7.85-286.71 g.The b value 2.1299 was less than 3 indicating that the growth pattern of the fish was allometric.The correlation co-efficient(r)value for S.melanotheron was 0.7528.The condition factor for the combined sexes fluctuated monthly.The length-weight relationships and condition factor of S.melanotheron in Forcados river estuary indicated that the fish were above average condition.
文摘This paper reviews the significant contribution of hydrologic continuity in the development, evolution and fate of the Niger Delta. Formed from the aggregation of sediments from a drainage catchment area of over 2 million km<sup>2</sup>, the Niger Delta has evolved into a prolific sedimentary basin with a dense network of rivers and creeks. The ecological system is in a fragile state with fresh and saline water ecosystems maintaining a dynamic equilibrium. Rainfall typically varies from 2500 - 4000 mm per year compared to average annual evaporation of about 1500 mm, resulting in net antecedent moisture. Over 70% of the rainfall occurs in 4 months between May and September, creating a potential for flooding. Water level varies from less than 1.5 m in the estuaries to about 8 m at the apex of the delta, with Nun River having a slightly higher elevation compared to Forcados River, implying that canals connecting both rivers at the same reach would experience water movements from Nun to Forcados River. Similarly, water level gradients vary across the stretch of the rivers from 8.6 to 9.5 × 10<sup>-5</sup> (cm/km) between Onitsha and Asamabiri, 7.5 to 7.7 × 10<sup>-5</sup> (cm/km) on the Forcados River downstream of Asamabiri, and from 7.4 to 7.6 × 10<sup>-5</sup> (cm/km) on the Nun River. At peak flood, about 23 × 10<sup>3</sup> m<sup>3</sup>/sec of runoff enters the Niger Delta. At the same time, about 16 × 10<sup>3</sup> m<sup>3</sup>/sec discharges from the estuaries into the ocean in a semi-diurnal tidal flow leaving a surplus that accumulates to cause flooding. The delta thus acts like a sponge, absorbing the shear amount of flow and releasing slowly stored water through at least twenty-one outlet estuaries into the Atlantic Ocean. The shear amount of discharge overwhelms the capacity of the network of distributaries and predisposes the delta to flooding. Assessment of the capacity of the rivers to evacuate pollutants showed that rivers to the west of Brass which are fed by Forcados River exhibited relatively stronger flux efficiencies prior to 1998 but are presently weaker compared to rivers fed by Nun. The rivers to the east between New Calabar and Imo Rivers exhibited very weak ebb tide asymmetry or net upstream flow largely because these rivers receive little or no freshwater influx from upstream sources. Flood and erosion are the major hydrological hazards in the region.
