| dc.description.abstract | Fish was sampled within the Sabaki River estuary for a period of 6 months (January to
June 2003) on monthly basis, during the last quarter of the lunar cycle (neap tide) at low
water tide. The physico-chemical parameters investigated included rainfall, temperature,
salinity, water transparency, total suspended sediments (TSS) and chlorophyll a (Chl-a)
concentrations. The broad objective of this study was to investigate environmental
gradients and how they influence seasonal and spatial variation in fish community
structure and distribution in the River Sabaki estuary. This was tested against the
hypothesis that estuarine hydrodynamics significantly influenced fish communities at the
estuary and adjacent coastal waters. The study area was divided in to 5 zones designated
SBKO, SBKl, SBK2, SBK3 and SBK4, based on salinity gradient. Each stratum was
sampled independently and data pooled to give overall results. Data on rainfall was
obtained from Malindi meteorological station, a standard mercury thermometer was used
to measure temperature, salinity was determined using a hand held refractometer and a 30
em diameter secchi disk was used to estimate water transparency. Total suspended
sediments (TSS) concentration in the water was determined using gravimetric methods as
described by Strickland et. al. (1972) and Mudroch and Macknight (1994). Water
samples were filtered through oven-dried and pre-weighed GF/C glass micro-fibre filters.
The filters and sample were dried to a constant weight. The dry weight of TSS was then
estimated. Chlorophyll a (ChI - a) concentration in the water samples was determined
using spectrophotometric method as described by Parsons et. al. (1989). Water samples
were passed through GF/F glass micro-fibre filters. The filters were placed in stoppered
glass tubes and centrifuged in 10 ml 90% Acetone (Analyzer grade). The supernatant was
decanted and extinctions measured in 650 nm, 664 nm, 647 nm and 630 nm wavelengths
using a zeroed spectrophotometer. Fish samples were collected by seining using nets of
10 mm and 20 mm knot -knot mesh sizes, measuring 2 m deep and 45 m long. Two
hauls of 15 minutes each were made at each sampling station. Fish collected was
identified to species level where possible. Multivariate analysis of variance (MANOV A),
multiple regression analysis, F- test, t-test, Principal Component Analysis (PCA) and
Canonical Correspondence Analysis (CCA) were performed on the data sets to test for
any significant differences between the parameters. Results showed that January to
March were dry. Rainfall peaked in May (22.1 mm). March recorded the highest mean
water temperature, 36.5 °c while highest mean air temperature was in April, 34.04 "C.
Salinity gradient was observed. SBKO recorded the highest mean salinity levels, 4.43 %0,
significantly differing from others (P < 0.05). The difference in spatial variation in TSS
was not significant (P > 0.2). Highest amount of TSS was recorded in the Mid stations,
0.334 mg/l - 0.335 mg/I. Mean TSS concentration between the dry and wet seasons was
significantly different (t = 0.208, F = 4.87,P"< 0.05). May recorded highest TSS levels,
0.52 mg/l while lowest in March, 0.063 mg/I. Highest amounts of Chl-a was recorded in
June, 226.4 mg/l and lowest was in March, 29.33 mg/I. The difference in spatial variation
in Chl-a was significant. SBKI had the highest levels, 107 mg/I. A total of 10,807
individuals of fish and crustaceans were caught in the sample. | en |
