Aspects of the ecology of Etse Lagoon: Implications for small scale fisheries management at Abandze, Ghana

Abstract

Aspects of the ecology and spatial context of Etse Lagoon at Abandze, in the Central Region of Ghana were studied from April 2014 and March 2015. Water temperature ranged from 24.0 ⁰C to 36.6 ⁰C (mean = 29.43 ± 0.12 ⁰C). Salinity varied from 0.72 ‰ to 22.30 ‰ (mean = 13.42 ± 0.30 ‰), pH from 4.6 to 8.9 with a mean value of 7.6 ± 0.03, DO from 1.65 mg/l to 11.15 mg/l with a mean value of 5.08 ± 0.08 mg/l and conductivity from 7.35 mS/cm to 43.3 mS/cm with a mean value of 18.58 ± 0.44 mS/cm. Eighteen fish species comprising 15 fin fish and 3 shell fish were sampled in the lagoon. The dominant fish species, Sarotherodon melanontheron comprised 74 % of the total catch and ranged in length from 7.0 cm to 7.9 cm standard length. The following characteristics were estimated for the population: growth constant K = 0.93 yr-1; asymptotic length L∞ = 14.25 cm of SL; longevity tmax = 3.2 years; theoretical length at age zero t0 = -2.23 cm and the growth performance index, Φ′ = 2.28. The total mortality rate Z was estimated at 5.09 yr-1, natural mortality M at 2.15 yr-1, fishing mortality, F at 2.95 yr-1 and the exploitation rate E as 0.58. Recruitment occurred throughout the year with two peaks representing minor and major recruitment seasons. Shannon-Wiener index H‟ ranged from 0 to 2.15 and the mean was 0.76 ± 0.17, Margaleff index d, 0 to 2.28 (mean = 1.07 ± 0.21) and Simpson‟s dominance D, 0 to 1.80 (mean = 0.64 ± 0.13). The fringe mangrove forest at Etse Lagoon can be described as having an intermediate structural development. Geographic information system information shows that the surface area of the lagoon has decreased about 2.86 % between 1973 and 2012.