INFLUENCE OF RAINFALL AND SALINITY ON THE SPAWNING CYCLE OF Nematopalaemon hastatus IN RIVER NUN ESTUARY,

BAYELSA STATE, NIGER DELTA.
1Ngodigha S.A, 2Digha O.N. and 3Adeyemo A.
1&2Bayelsa State College of Education, Okpoma,
Yenagoa, Bayelsa State, Nigeria
3Niger Delta University, Wilberforce Island,
Amassoma, Bayelsa State, Nigeria.
E-mail: sabinaingodigha@yahoo.com
ABSTRACT
Spawning pattern of Nematopalemon hastatus in River Nun Estuary,
Bayelsa State in the Niger Delta was studied for one year. Samples
were collected from artisanal shrimpers operating along the estuary on
a monthly basis and stored in 9% formalin for laboratory analysis. The
N. hastatus in each monthly sample were observed for gravity, using a
hand lens. There was a colour change in the eggs from light orange to
dark brown with maturation. Eggs in different stages of maturation
from light orange to dark brown were observed in the samples all year
round, comprising both rainy and dry seasons. Main spawning observed
was between July and September. The peak spawning activity occurred
in September while the lowest was between November and December.
Largest satus with eggs measured 14mmCL (carapace length) and the
smallest 7mmCL. Statistical analysis to test the level significance of
gravid N. hastatus between seasons showed that more spawners were
landed during the rainy season than the dry season. Spawners are
usually caught before they have the chance to lay their eggs and this
could lead to a reduction in the reproductive process, resulting in a
decrease in biomass. It is therefore pertinent to introduce management
strategies involving, fisheries scientist, fisheries managers and the
shrimpers.