Abstract

The fish species of the lower Nun River was sampled to determine gillnet selectivity and the effect of season, tide and photoperiod variation on the catch. A total of 11,156 specimens were caught belonging to 14 families consisting of 25 species. Gillnet selectivity was observed with a declining trend from the largest mesh size net of 15 mm (58%) in number and 59% by weight, 12 mm (33%) in number and 33% by weight with the least catch of about 9% by number and 8% by weight from the smallest (8 mm) net. In terms of seasonal variation, the rainy season catches were significantly higher (P< 0.05) than the dry season with relative abundance of 67 and 32% respectively. Tidal variation in the catches showed that catches were higher during the low tidal period (61%) than the high tide (39%). Significant photoperiod differences (P < 0.05) were observed with higher catches by day (58%) than by night.

Key words: Gillnet selectivity, seasonal, tidal, photoperiod, variation, Nun River.