| dc.description.abstract | This study describes the reproductive biology and fishery of Plectorhinchus
flavomaculatus during the Northeast and Southeast monsoon within the Kenyan inshore
marine waters. The study covers the period from January to December 2001. The results
are based on 552 specimens collected from the Kisite Mpunguti Marine reserve, Shimoni
using traditional traps.
The population of this species showed an overall sex ratio of 1:1.3 in favour of the
females. The ratio however did not depart significantly from the 1:1 male to female ratio
(X 2 =5.899, p < 0.824, d.f =10).
P. flavomaculatus displayed isometric growth rate with the length weight relationship
being symmetrical between the sexes. Males and females were pooled in the subsequent
analysis with the overall length (TL) weight (Wt) relationship described by the equation,
Wt = 0.026Te·83 r2=0.95
Where;
Wt= Weight
TL = Total length •
r2 = Correlation coefficient.
Temporal variation of the relative condition of the fish was observed throughout the period
of the study. Two distinct peaks were observed for females one corresponding to April (K,
= 1.20 ) and the other to September (Kn= 1.33). Males also displayed two distinct peaks
closely corresponding to the females' seasonal peaks, The peaks were a minor one in
April (K, =1.02) and the-other in September (K, = 1.31). Temporal variation of the relative
condition factor was influenced by the spawning period of the species.
Based on both histological examination on the internal organization of the ovary and the
macroroscopic appearance of the gonads i.e. colour, texture, degree of vascularization,
gonad length and gonad width, of this species, seven distinct maturity stages were clearly
identified. The seven maturity stages were immature virgins, developing virgins,
recovenng mature, mature, npe, running and spent. In addition, both histological
examination on the internal organization of the ovary and oocyte size distributions of
portions of the same ovary preserved in Gilson's fluid showed that oocyte development in
Plectorhinchus flavomaculatus was asynchronous.
The percentage occurrence of mature fish in the samples together with the pattern of
changes in gonad weight indicated that the fish had an extended spawning season falling
within the Northeast monsoon.
From the length frequency data, a quantitative study of the fishery of P. flavomaculatus
involving determination of growth using the Von Bertalanffy growth model, mortality,
recruitment patterns and relative yield-per-recruit (Y'/R) yielded the following results.
Using Powell-Wetherall plot procedure in FiSAT software, the seasonalized Von
Bertalanffy growth coefficients were L, = 64.81 Total length (ern), K = 0.49, to = -0.26.
The overall Von Bertalanffy grow,th model was thus explained by the equation Lt= 64.8[1-
e-O.49(t+O.26)]. The seasonalized len~th converted catch curve yielded an instantaneous total
mortality coefficient of Z = ·1.78 per year. The instantaneous natural mortality was
determined using Pauly's e9uation and was equal to M = 0.93, while the instantaneous
fishing mortality was F = 0.85 per year. The exploitation rate of this species was E = 0.48.
Biomass per recruit was computed using Beverton ana Holt (Beverton and Holt, 1957)
biomass per recruit function. Using the knife edge Brocedure Emax was equal to 0.59 , EO.l
(value of E at which marginal increase in the B'/R ;S"1O%of it's value at E = 0) 0.51 and
E05(the value of Eat 50% of the exploited relative biomass per recruit) 0.32. | en |
