The Effectiveness of School Heads Towards Enhancing Students’ Academic Performance in Secondary Schools in Urban District - Unguja.

Poor student’s academic performance is a serious problem facing public secondary schools both in the Mainland Tanzania and Zanzibar. This study the effectiveness of school heads towards enhancing student’s academic performance in Urban District in Unguja-Zanzibar has been assessed using five secondary schools. Target population comprised of five school heads and eighty-five informants, namely one District Education Officer, five head prefects, twenty-five teachers, forty-five students and nine school committee members. The study used descriptive survey design with questionnaires and interviews as data collection instruments. School heads in poorly performing schools were found with skill deficiencies in carrying some management and leadership duties for effective enhancement of student’s academic performance such as (i) development of appealing school visions and their effective communication to stakeholders to rally support and assistance, (ii) effective supervision/monitoring of teaching and learning processes, and (iii) development of motivation systems for promoting teaching and learning processes. School heads of better performing schools (a) had more regular tendency of supervising teachers’ and students’ academic works, (b) were clearer in motivation system used to promote teaching and learning, (c) attended their classes more regularly than those in low performing schools. In view of the findings, it was concluded that the more the school heads were equipped with skills relevant for promoting effective teaching and learning, the greater were the impacts of such school heads. It is recommended that school heads recruitment processes should consider assessing management and leadership skills and in-service training sessions to update such skills. Key words: Academic, Effectiveness, Performance, Secondary School

Charge Localization and Ordering in A2_2Mn8_8O16_{16} Hollandite Group Oxides: Impact of Density Functional Theory Approaches

The phases of A$_2$Mn$_8$O$_{16}$ hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in Density Functional Theory. Three examples (A = Ag, Li and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn $3d$ electrons are more explicitly considered with the DFT+$U$ approach. Finally selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low $U$ and a high $U$ approach. In the low $U$ case, the materials are described as band metals with a high symmetry, tetragonal crystal structure. In the high $U$ case, the electrons donated by A result in formation of local Mn$^{3+}$ centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. . . .Comment: 16 pages, 8 figure

Local Victory: Assessing Interspecific Competition in Seagrass From a Trait-Based Perspective

Tropical seagrass meadows are formed by an array of seagrass species that share the same space. Species sharing the same plot are competing for resources, namely light and inorganic nutrients, which results in the capacity of some species to preempt space from others. However, the drivers behind seagrass species competition are not completely understood. In this work, we studied the competitive interactions among tropical seagrass species of Unguja Island (Zanzibar, Tanzania) using a trait-based approach. We quantified the abundance of eight seagrass species under different trophic states, and selected nine traits related to light and inorganic nutrient preemption to characterize the functional strategy of the species (leaf maximum length and width, leaves per shoot, leaf mass area, vertical rhizome length, shoots per meter of ramet, rhizome diameter, roots per meter of ramet, and root maximum length). From the seagrass abundance we calculated the probability of space preemption between pairs of seagrass species and for each individual seagrass species under the different trophic states. Species had different probabilities of space preemption, with the climax species Thalassodendron ciliatum, Enhalus acoroides, Thalassia hemprichii, and the opportunistic Cymodocea serrulata having the highest probability of preemption, while the pioneer and opportunistic species Halophila ovalis, Syringodium isoetifolium, Halodule uninervis, and Cymodocea rotundata had the lowest. Traits determining the functional strategy showed that there was a size gradient across species. For two co-occurring seagrass species, probability of preemption was the highest for the larger species, it increased as the size difference between species increased and was unaffected by the trophic state. Competitive interactions among seagrass species were asymmetrical, i.e., negative effects were not reciprocal, and the driver behind space preemption was determined by plant size. Seagrass space preemption is a consequence of resource competition, and the probability of a species to exert preemption can be calculated using a trait-based approach

The Need of a Structured Tilapia Breeding Program in Tanzania to Enhance Aquaculture Production: A Review

Breeding programs are crucial for boosting productivity and increase sustainability of aquaculture. Over years, Tanzania has witnessed fluctuation in its capture fisheries production from 320,900 to 375, 535 and back to 362,595 metric tonnes in the years 2000, 2005 and 2016, respectively (URT 2016). The declining trend in fish production has made fish supply in the country unstable and conversely, increased the demand for fishes to about 730,000 metric tonnes in 2017. However, the local aquaculture production has not increased accordingly. Tanzania is importing fish mainly from Asia to meet its increased demand. In 2017, a total of 2,055,721 kg of frozen tilapia were imported from China and Mozambique (URT 2017). The introduction of exotic fish species in Tanzania should be carefully managed because introduced species have many negative impacts to the indigenous species. Tanzania should have a moderate scale tilapia breeding program that will produce good quality fingerlings at affordable price for smallholder fish farmers. The availability of reliable good quality fingerlings is key to improve aquaculture production in the country. Among 17 existing hatcheries, only 12 hatcheries are active, however these hatcheries are not performing well due to low investment and technology leading to the production of low quantity and quality fingerlings. The need for a structured sustainable Tilapia breeding program with bio secured and reliable hatcheries to enhance aquaculture production in Tanzania is given in this review.Keywords: Aquaculture, Breeding programs, Nile tilapia, Local strains

Halocarbon emissions by selected tropical seaweeds: species-specific and compound-specific responses under changing pH

Five tropical seaweeds, Kappaphycus alvarezii (Doty) Doty ex P.C. Silva, Padina australis Hauck, Sargassum binderi Sonder ex J. Agardh (syn. S. aquifolium (Turner) C. Agardh), Sargassum siliquosum J. Agardh and Turbinaria conoides (J. Agardh) Kützing, were incubated in seawater of pH 8.0, 7.8 (ambient), 7.6, 7.4 and 7.2, to study the effects of changing seawater pH on halocarbon emissions. Eight halocarbon species known to be emitted by seaweeds were investigated: bromoform (CHBr3), dibro-momethane (CH2Br2), iodomethane (CH3I), diiodomethane (CH2I2), bromoiodomethane (CH2BrI), bromochlorometh-ane (CH2BrCl), bromodichloromethane (CHBrCl2), and dibro-mochloromethane (CHBr2Cl). These very short-lived halocarbon gases are believed to contribute to stratospheric halogen concentrations if released in the tropics. It was observed that the seaweeds emit all eight halocarbons assayed, with the exception of K. alvarezii and S. binderi for CH2I2 and CH3I respectively, which were not measurable at the achievable limit of detection. The effect of pH on halocarbon emission by the seaweeds was shown to be species-specific and compound specific. The highest percentage changes in emissions for the halocarbons of interest were observed at the lower pH levels of 7.2 and 7.4 especially in Padina australis and Sargassum spp., showing that lower seawater pH causes elevated emissions of some halocarbon compounds. In general the seaweed least affected by pH change in terms of types of halocarbon emission, was P. australis. The commercially farmed seaweed K. alvarezii was very sensitive to pH change as shown by the high increases in most of the compounds in all pH levels relative to ambient. In terms of percentage decrease in maximum quantum yield of photosynthesis (Fv∕Fm) prior to and after incubation, there were no significant correlations with the various pH levels tested for all seaweeds. The correlation between percentage decrease in the maximum quantum yield of photosynthesis (Fv∕Fm) and halocarbon emission rates, was significant only for CH2BrCl emission by P. australis (r = 0.47; p ≤ 0.04), implying that photosynthesis may not be closely linked to halocarbon emissions by the seaweeds studied. Bromine was the largest contributor to the total mass of halogen emitted for all the seaweeds at all pH. The highest total amount of bromine emitted by K. alvarezii (an average of 98% of total mass of halogens) and the increase in the total amount of chlorine with decreasing seawater pH fuels concern for the expanding seaweed farming activities in the ASEAN region

Rates and controls of the air-sea flux of bromoform (CHBr3): a review and synthesis

Bromoform (CHBr3) is the largest single source of atmospheric organic bromine and therefore of importance as a source of reactive halogens to the troposphere and lower stratosphere. The sea-to-air flux, originating with macroalgal and planktonic sources, is the main source for atmospheric bromoform. We review bromoform's contribution to atmospheric chemistry, its atmospheric and oceanic distributions and its oceanic sources and sinks. We have reassessed oceanic emissions, based on published aqueous and airborne concentration data, global climatological parameters, and information concerning coastal and biogenic sources. The goals are to attempt an estimate of the global source strength and partly to identify key regions that require further investigation. The sea-to-air flux is spatially and temporally variable with tropical, subtropical and shelf waters identified as potentially important source regions. We obtain an annual global flux of bromoform of ∼10 Gmol Br yr−1 (3–22 Gmol Br yr−1). This estimate is associated with significant uncertainty, arising from data precision and coverage, choice of air-sea exchange parameterizations and model assumptions. Anthropogenic sources of ∼0.3 (to 1.1) Gmol Br yr−1 (as CHBr3) can be locally significant, but are globally negligible. Our estimate of the global oceanic source is three to four times higher than recent estimates based on the modeling of atmospheric sinks. The reasons for this discrepancy could lie with the limited regional and temporal data available and the broad assumptions that underlie our flux calculations. Alternatively, atmospheric sink calculations, often made on the basis of background CHBr3 levels, may neglect the influence of strong but highly localized sources (e.g., from some coastal and shelf regions). The strongly variable and poorly characterized source of CHBr3, together with its short atmospheric lifetime, complicates model-based estimation of the distribution of reactive Br resulting from its atmospheric degradation. An integrated program of marine and atmospheric observations, atmospheric modeling and mechanistic studies of oceanic bromoform production is required to better constrain present and future Br delivery to the atmosphere

Effects of waterlogging, salinity and light on the productivity of Bruguiera gymnorrhiza and Heritiera littoralis seedlings

This study aimed to establish the effects of waterlogging, salinity and light on the early development of mangroves. Seedlings of Bruguiera gymnorrhiza (L.) Lamk. and Heritiera littoralis Dryand were exposed to 12 weeks of waterlogging, during which time growth and photosynthesis were measured every two weeks. The salinity of the water inundation ranged from fresh water to full-strength sea water (salinity 35). Seedlings were exposed to either full sunlight of 1 500 μmol photon m–2 s–1 (SD 397) at midday or shade conditions of 325 μmol photon m–2 s–1 (SD 40) of light at midday, to explore whether the plants would be differently affected by prolonged waterlogging in increased salinities and under different light conditions. Heritiera littoralis was more sensitive to waterlogging, salinity and light, displaying a least relative growth rate of 0.127 g g–1 week–1 (SE 0.032) under shade, and 0.025 g g–1 week–1 (SE 0.021) in full light; while under shade, photosynthesis continued only in fresh water, but photosynthetic yield decreased from 0.7 to 0.4 with increasing duration of waterlogging. By 12 weeks, all H. littoralis seedlings treated with any saltwater mixture had died. Bruguiera gymnorrhiza seedlings maintained a moderate rate of photosynthesis throughout inundation in both shade and full light, with yields of 0.7 and 0.3, respectively. Furthermore, B. gymnorrhiza survived waterlogging in up to 66% seawater, and maintained comparable relative growth rates of 0.164 g g–1 week–1 (SE 0.066) with 0.083 g g–1 week–1 (SE 0.065) and 0.074 g g–1 week–1 (SE 0.036) with 0.052 g g–1 week–1 (SE 0.037) under shade and in full light between fresh water and the highest salinity conditions, respectively. These results suggest that B. gymnorrhiza is broadly tolerant, making it a potential candidate species for restoring vulnerable mangrove forests.Keywords: ecophysiology, growth, mangrove forests, mesocosm experiment, photosynthetic yield, surviva

Growth performance of five different strains of Nile tilapia (Oreochromis niloticus) introduced to Tanzania reared in fresh and brackish waters

Five introduced strains of Nile tilapia (Oreochromis niloticus) were tested for growth performance both in fresh- and brackish-water (2 salinity units) environments for 56 days. The BIG NIN, GIFT, Chitralada, "Ruvu Farm" and Silver YY strains with initial mean average weight (+/- standard error) of 96.4 +/- 6.90 g, 104.1 +/- 7.19 g, 137.2 +/- 7.21 g, 53.2 +/- 6.98 g and 95.3 +/- 7.11 g, respectively were used. Individuals were tagged and pooled in hapas (12 mx8.5 mx2 m each), aligned into different ponds (20 mx20 m each). Stocking density of 5 fish/m(2) and 350 g/kg crude protein diet were used. Overall, the average weight gain for GIFT strain was 7.5%, 32%, 45% and 86.5% higher than BIG NIN, Chitralada, "Ruvu Farm" and Silver YY strains, respectively, across both environments. All strains performed significantly better (p<0.05) when reared in brackish-water than their respective counterparts in freshwater, except for the BIG NIN strain. The morphometric correlations for all strains in both environments ranged from moderate (0.50) to strong positive (0.92). The GIFT strain demonstrated superior growth and genotype by environment interaction was weak and not important to be prioritized in breeding programs