Illegal, unregulated and unreported (IUU) fishing is a negative social vice that adversely affects global capture fishery production. The inadequate disclosure of IUU methods and trends in fishery waters hampers management actions to curb illegal fishing activities. Seldom have empirical studies been conducted on IUU methods and their trends in Lake Naivasha. Therefore, this study analysed data on the fisheries monitoring, control and surveillance (MCS) during 2012 to 2018 to test for the significance of trends, and compare the enforcement plans to seizures of illegal fishing gear in the lake. The IUU fishing methods included both the types of equipment and the means used to perpetrate illicit capture or acquisition of fish from the lake. The results indicate a 37% reduction of MCS enforcement patrols during 2018 compared to 2012, and a 16% to 100% upsurge in the quantity of seized IUU fishing items. Illegal fishing boats potentially threaten the fishery of Lake Naivasha with an additional fishing effort of 22% above the 176 licensed boats. An average of 10,700 fishing nets seized per year has the potential fishing intensity of 74 gillnets/km2 against an ideal intensity of 12 gillnets/km2. The frequencies of MCS patrols in Lake Naivasha exhibit no particular trends and likely ineffective in deterring the upsurge of IUU activities, or the evolution of new illegal fishing methods. An increased seizure of illegal fishing boats, outboard engines and gillnets could imply their rampant use in IUU fishing activities. These findings merit a multi‐stakeholder participatory approach to identifying the MCS weaknesses and opportunities for sharing resources to strengthen the fishery management efforts in Lake Naivasha.
Nile tilapia Oreochromis niloticus (L.) is a recent re-introduction in Lake Naivasha and is one of the fish species that has crossed into Lake Oloidien. This study assessed and compared the population characteristic of O. niloticus under different physicochemical conditions of water in L. Naivasha (main) and L. Oloidien. Samples of water for selected water quality parameters and fisheries data from catch survey were collected between 2017 and 2018. Results indicate the highest conductivity levels recorded in 2018 as 2916 ±11.30 µScm-1 and 282.33 ± 4.33 µScm-1 for L. Oloidien and L. Naivasha respectively. Mean total lengths of O. niloticus were 19.1± 1.8 cm and 23.6 ± 2.9 cm for L. Oloidien and L. Naivasha respectively. Mean weight of O. niloticus was 129.3 ± 37.8 g in L. Oloidien and 260.9 ± 81.0 g in L. Naivasha. Length-weight relationship analysis showed a negative allometric growth (b = 2.526) and (b = 2.983; p > 0.05) in lakes Oloidien and Naivasha respectively. The relative condition factor (Kn) values were slightly lower in O. niloticus from L. Oloidien compared to the main Lake. Differences between the two lakes in the population characteristics of O. niloticus may be attributed to the observed differences in the habitat conditions, including the conductivity and pH levels.
Hydrological dynamics affect water levels and thus affecting ecosystem structure and functions. Lake levels in tropical ecosystems affect phosphorous input through runoff from adjacent watersheds. The resultant biological community, water and sediment quality of the lakes due to water level changes is a reflection of the geology of the area and the anthropogenic activities in the watershed. The study conducted between January 2018 and December 2019 was to explore relationships between the phosphorous input and Water Level Fluctuations (WLF) recorded by Water Resource Authority (WRA). Lake water samples were analyzed in the laboratory for phosphorous using molybdenum blue-ascorbic method and recorded using spectrophotometer.Chlorophyll-a was determined by extracting a filtered sample with 15 ml acetone and incubating overnight and thereafter read using a double beam spectrophotometer. Total Suspended Solids (TSS) was determined by filtering 200 ml of a water sample and dried overnight at 105˚C. The lowest and highest phosphorous concentrations recorded were 0.2 mg/l and 0.42 mg/l at NST7 and NST2, respectively. Measurements of Chlorophyll-a were 0.32 mg/l and 0.42 mg/l at NST9 and NST2, respectively. Secchi transparency measurements were 32.9 cm at NST3 and 84 cm at NST1. The highest and lowest TSS concentrations were 0.14 mg/l and 0.13 mg/l at NTS1 and NST8, respectively. The hydrodynamic regime in most tropical lakes plays a signifi-
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