Length-weight relationship of selected teleost fishes from Kilifi County, Kenya

Sustainable exploitation of fishery resources requires knowledge of the population dynamics of the target resources. Length-weight relationship and relative condition parameters were determined for nine teleost fish species, Calotomus carolinus (Valenciennes, 1835), Decapterus macrosoma (Bleeker, 1851), Lethrinus nebulosus (Forsskal, 1775), Lethrinus harak (Forsskal, 1775), Lutjanus fulviflamma (Forsskal, 1775), Rastrelliger kanagurta (Cuvier, 1816), Sargocenton caudimaculatus (Ruppel, 1838), Scomberoides tol (Cuvier 1832) and Siganus sutor (Valenciennes, 1835). The fish were randomly collected from artisanal fishers who operated gears such as gill nets, spearguns and basket traps at three landing sites in Kilifi County between February and April 2017. The linear regression revealed a positive relationship between total length and body weight in all the fish sampled. The t-test calculated on b for most species revealed no significant deviations from the expected cube value of three, except for L. nebulosus (t=0.340, p<0.05), R. kanagurta (t=1.321, p<0.05) and S. sutor (t=0.961, p<0.05). These fish populations are healthy as shown by a relative condition factor above 1 in all species, suggesting that the nutritional requirements are available in the ecosystem, and that the Kilifi coral reefs have thus not been degraded.

Vegetative and reproductive phenological traits of Rhizophora mucronata Lamk. and Sonneratia alba Sm.

Mangrove phenology is important in understanding the past, present and future response of mangrove species to impacts of climate change. Our study is the first long term direct observation of the phenology of Rhizophora mucronata and Sonneratia alba in Kenya. Objective of the study was to determine, interpret and document the timing of the various phenoevents and phenophases, and to establish relationships between phenology and the climatic variables. Phenological traits were investigated in six monospecific mangrove stands in Gazi Bay, south of Mombasa, for 2 years. Leaf emergence, leaf fall, flower bud, flower and fruit initiation data were recorded every fortnight in 54 shoots of 9 trees at each site. Continuous leaf emergence and loss characterized by multimodal peaks was observed for the two species. Leaf emergence and leaf fall peaked in the wet months and was reduced in the dry months. There was a relationship between the leaf emergence and drop with the reproductive phenology in the two species. Mean leaf longevity for R. mucronata and S. alba was 12.8. ±. 1.2 and 4.9. ±. 0.5 months respectively. The reproductive cycle took approximately 16-20 months in R. mucronata and 4-5 months in S. alba. Bud initiation in R. mucronata was seasonal and occurred in October and September. Buds were observed for 8-11 months developing slowly on the shoots. Shifts were observed in the timing of flower initiation, and the flowering period lasted in total for 4-5 months. The time period from flower appearance to the developmental start of immature propagules lasted about 1 month at reforested sites and up to 5 months in stands of natural vegetation. In R. mucronata initiation of immature propagules was not seasonal and varied among the sites. Fruiting in S. alba was short and seasonal without overlap, and shifts were observed in the timing of flowering, flowering and fruiting peaks. Abscission of reproductive parts started in July and in June, respectively, in the years 2005 and 2006. Fruiting was observed starting in August in both years, and fruiting peak was reached in October in 2005 and one month earlier in 2006. In R. mucronata vegetative and reproductive phenophases significantly correlated with climatic variables, whereas in S. alba only leaf emergence and leaf fall correlated with temperature. The flowering plasticity in the reproductive phenology of the two species indicates possible sensitivity to certain climatic and environmental triggers. Our results also indicate that R. mucronata trees have a distinctly higher investment in the reproductive cycle than S. alba. © 2013 Elsevier GmbH.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Litter Fall Dynamics of Restored Mangroves (Rhizophora mucronata Lamk. and Sonneratia alba Sm.) in Kenya

Mangrove forests are active carbon sinks and important for nutrient cycling in coastal ecosystems. Restoration of degraded mangrove habitats enhances return of ecosystem goods and services, including carbon sequestration. Our objective was to assess the restoration of primary productivity of reforested mangrove stands in comparison with natural reference stands in Gazi Bay, Kenya. Litter fall data were collected in nine Rhizophora mucronata and Sonneratia alba monospecific stands by use of litter traps over 2 years. Litter was emptied monthly, dried, sorted, and weighed. The reforested and natural stands showed seasonality patterns only in the production of reproductive material. Leaves constituted the highest percentage to total litter fall. Litter productivity rates for the R. mucronata stands were not significantly different and ranged from 6.61-10.15 to 8.36-11.02 t ha-1 yr-1 for the restored and natural stands, respectively. The productivity of 5 years R. mucronata stands reached 5.22 t ha-1 yr-1 and was significantly different from other stands. Litter productivity rates for S. alba stands was 7.77-7.85 for the restored stands and 10.15 t ha-1 yr-1 for the natural stand but differences were not significant. Our results indicate that plantations of at least 11 years have attained litter productivity rates comparable to the natural forests. This suggests that productivity of replanted mangroves is likely to reach complete recovery by this age under the prevailing environmental conditions.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe