Biophysical factors influencing the choice of nesting sites by the green turtle (Chelonia mydas) on the Kenyan coast

The green turtle (Chelonia mydas) is the most common sea turtle nesting along Kenya’s coastline. Varying biophysical factors influence choice of nesting sites where eggs are laid. This study was conducted between February and November 2016 and was designed to establish the relationship between numbers of C. mydas nests on the beach and biophysical variables such as vegetation cover, organic matter content (OMC), beach width, and beach slope. Multiple regression analysis was employed to assess the factors that contribute to the number of C. mydas nests on a beach. This analysis did not allow prediction of the number of nests in a statistically significant way (F (4, 26) = 0.094, p > 0.05, R = 0.120). However, there was a decrease in the number of nests with increased vegetation cover (b = - 0.013), OMC (b = - 8.114), beach width (b = - 0.089) and slope of the beach (b = - 0.352). Approximately 70% of nests occurred on beaches with medium and fine sand. Beaches with intense human activities were associated with high OMC which significantly affected the number of nests on the beach. It is therefore recommended that existing laws should be enforced to control beach development and human activities along the Kenyan coast to protect nest sites. Additionally, long term monitoring should be put in place to evaluate the impact of human disturbance on the favourable biophysical factors influencing the number of nests on a beach, as a management tool in the conservation of C. mydas.

Population, flocking behaviour and habitat selection of the Grey Crowned Crane Balearica regulorum at Lake Ol’ Bolossat basin, Kenya

Lake Ol’ Bolossat is an inland wetland located in Nyandarua County, Kenya that provides critical year-round habitat for the Globally Endangered Grey Crowned Crane Balearica regulorum gibbericeps. This study aimed at establishing the population size and density of cranes in the basin, ratio of young to adults (as a measure of productivity), and habitat selection and use during the breeding and non-breeding seasons. Using complete ground counts, five censuses were conducted between 2017 and 2020 with between 521 and 1115 cranes recorded, and we estimate the local population size to be 250–350 individuals. Population density ranged from 0.99–2.18 cranes/km2 during the breeding and non-breeding seasons respectively. From all 219 observations made during the study period, the  mean flock size was 28.21 with a maximum flock size of 332 and a modal flock size of 2–25 individuals. The average proportion of young cranes across all counts was 11.65% indicating a population which is breeding successfully. Although cranes occupied both wetlands and terrestrial habitats in almost equal proportions across the year cumulatively, the difference in choice of habitat between the breeding and the non-breeding seasons was significant (χ2=489, df=1, p=0.0001), whereby more cranes (mostly paired individuals) were observed in marshes during breeding months. Wheat fields were the most often used of terrestrial habitats among fields of different crop types sampled. Holding 14% and 5% of Kenya’s and the global population of Grey Crowned Cranes, respectively, Lake Ol’Bolossat is undoubtedly an important site for this species’ conservation and survival. Keywords: Lake Ol’ Bolossat, Balearica regulorum gibbericeps, habitat selection, population size, flock characteristic

On‐farm growth performance of different strains of tilapia, Oreochromis niloticus reared in earthen ponds

Abstract The growth of aquaculture sector in Kenya has been anchored on farmed Nile tilapia Oreochromis niloticus. Different strains of the species exist in Kenya with unknown quality due to lack of stock improvement programmes coupled by variations in breeding and management practices in different hatcheries. The seeds supplied to farmers have not exhibited good performance and resilience to changing climate. There is need to validate the quality of strains supplied to fish farmers in Kenya. This study sought to compare the growth performance of three strains of farmed Nile tilapia; Sagana strain (SAG‐F8) produced through selective breeding, super YY strain (KAM‐YY) from Kamuthanga fish farm and the local strain (LOC‐T) obtained from Siaya County. The fish were stocked in fertilised earthen ponds measuring 300 m2 in triplicates at 3 fish/m2. The fish were fed on 35% crude protein diet for 180 days at Bukani Aquapark located in Busia County, Kenya. There was no significant difference in mean weight gain (MWG) between SAG‐F8 and LOC‐T strain exhibiting 159.786 ± 6.76 g and 158.623 ± 4.67 g, respectively. However, under similar conditions, the KAM‐YY strain had a significantly lower MWG (131.74 ± 4.75 g) compared to the two strains. Food conversion ratio (FCR), specific growth rate (SGR) did not demonstrate any significant difference among the different strains. The body protein content in the SAG‐F8 fish strain was higher (65.40 ± 0.20%) followed by LOC‐T strain (61.23 ± 2.34%) and lastly KAM‐YY strain had the lowest (60.37 ± 0.89%). In this study, the impact of genetic improvement has been demonstrated to influence growth and feed efficiency as well as body composition. These improved strains will substantially increase fish production and productivity, hence, a positive impact on the fish farmers' livelihoods when supplied to the farmers and seed multipliers

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.