Efficiency and Selectivity of Monofilament Gillnet for Three Commercially Important Cichlids Species in Erelu Reservoir, Oyo, Nigeria

Abstract

Abstract

Gillnet selectivity is crucial for the effective and sustainable management of fisheries. However, there is a knowledge gap on gillnet selectivity for commercially important Tilapia species in EreluReservoir.Thisstudyestimated the selectivity parameters of commonly used monofilament gillnets for three commercially important cichlid species in Erelu Reservoi The reservoir was divided into upper, middle and lower zones based on geographical location Fleet of monofilament gill nets mesh sizes: 38.1, 50.8, 63.5, 76.2, 88.9, 101.6 and 127.0 mm were randomly set in each zone on a monthly basis for 21 months covering two wet and dry seasons, respectively. The catches were identified, counted and efficiency of each gillnet estimated for Oreochromis niloticus, Sarotherodon galileaus and Pelmatolapia mariae by calculating the catch-per-unit effort. The selectivity parameters such as Selection Factor (SF) and Selection Variance (SV) for each combined gillnets were determined from regression analysis while the Common Length of Selection (CLS) and optimum selection length were obtained from selectivity curve. The size at first maturity of the cichlids were determined using length frequency analysis wizard. Highest and least catch per unit effort for Oreochromis niloticus (76.2mm;127.0mm), Sarotherodon galileaus (76.2mm;127.0mm) and Pelmatolapia mariae (63.5mm;38.1mm) were 13.57g/m;0.20g/m,8.29g/m;0.10g/mand4.65g/m;0.40g/m,respectively.TheSF,CLSandSVfor the combined gillnet 76.2mm/63.5mm were 0.21;17.5cm; 2.91 and 0.19; 16.5cm and 1.86 for Oreochromis niloticus and Pelmatolapia mariae, respectively. The optimum selection length of 18.83cm (Oreochromis niloticus), 19.04cm (Sarotherodon galileaus) and 17.12cm (Pelmatolapia mariae), respectively were recorded for 76.2mm gillnet. Considering the size at first maturity of 17.9± 0.6cm, 16.5±0.2 and 15.0±0.3cm for Oreochromis niloticus, Sarotherodon galileaus and Pelmatolapia marie, respectively mesh size of 76.2mm will be appropriate for sustainable exploitation  of these  tilapia spp.in Erelu Reservoir