The recruitment patterns of two palaemon shrimps and some physico-chemical characteristics in the River Nun Estuary, Nigeria

Abstract

The

recruitment patterns of two palaemon shrimps, Nematopalaemon hastatus and Palaemon maculatus in the Nun River Estuary was studied for one year (2005-2006). In addition some physical and chemical parameters were measured to evaluate the characteristics of the fishery. The data obtained from the study showed that monthly surface water temperature values ranged from 210C (March-April) to 240C (July – September), salinity values from 9.0 Psu (July) to (21.3 Psu) (February). PH values ranged from 6.9 (December) to 8.2 (March). Rainfall values ranged from 30 mm (January) to 580 m (September). The main spawning season was between July and September. The lowest spawning activity occurred in November and December for both species. Both species were present all year round. N. hastatus was highest in September (63%) and lowest in November (57%), while P. maculatus was highest in November (43%) and lowest in September (37%). However, there was no significant difference in the monthly catch composition for both species. The seasonal spawning activity showed that spawning occurred all year round for both species. Peak spawning activity occurred in September for N. hastatus, while that of P. maculatus was August and September. The largest carapace length recorded was 14 mm for N. hastatus, while that of P. maculatus was 12 mm. More spawners were caught during the rainy season than dry season (Tcas = 3.04; Ttab = 0.025(5) = 2.571). Recruitment occurred all year round for both species, each with two peaks.

Keywords: Shrimps, spawning activity, physico-chemical characteristics, River Estuary, Nigeria