Barriers of persistent long-lasting insecticidal nets utilization in villages around Lake Tana, Northwest Ethiopia: a qualitative study

Background Malaria remains a major public health problem in Ethiopia. The use of LLINs is an effective approach to reducing transmission. Persistent use of LLINs is determined by numerous factors. Quantitative studies have assessed LLIN ownership and utilization, but the behavioral, socio-cultural, socioeconomic and net distribution contexts that impact their use have not been examined in depth. This study aimed to explore barriers of persistent LLIN use among communities around Lake Tana. Methods Twenty-three community residents who owned LLINs (15) or not (8) during the study period and 38 key informants were interviewed from April to June 2017. Phenomenological study was employed to explore the local contexts and factors that influence persistent use of LLINs. Individuals were purposefully selected to capture different views. Community residents were selected based on their permanent residence and LLIN use experience. Key informants were health extension workers, local leaders, students, and health professionals. The data were managed using QSR International NVivo Version 10 software and coded, and themes were identified. Results Killing ability of nets against arthropods other than mosquitoes reportedly made use of LLINs a favored malaria prevention method despite their ineffectiveness after 3 months. Conical nets were preferred due to their compatibility with varied sleeping structures. Numerous factors influenced persistent use, notably erroneous perceptions about LLINs, malaria and mosquitoes; bedbug infestation; inconvenience; unintended uses; distribution problem of nets; and socio-cultural and economic factors. Unintended uses were often associated with local needs and seldom linked with social issues and deficiencies in information about malaria and LLINs. Collateral benefits were considered important, principally in terms of disinfestation of bedbugs. Conclusions Non-persistent LLIN use was associated with inconvenient bed net design and early damage; non-potency of the insecticide against other arthropods; facilitation of bedbug infestation; unintended uses; wrong perceptions about malaria, mosquitoes, and LLINs; and inadequate follow-up regarding LLINs utilization. Distribution of conical nets and provision of adequate information on LLINs and malaria may promote persistent use. Using an insecticide that also kills arthropods other than mosquitoes may reduce unintended uses and increase persistent use.

Experimental Study on the Interaction Between the Net and the Weight System for a Gravity Type Fish Farm

The escape of salmon from aquaculture farms is considered a major problem for the industry. Structural failure is the dominating cause for escapes. One major issue is the contact, and subsequent abrasion between the sinker tube chain and the net, which has caused several large-scale escapes over the past years. Model tests were performed in a tow tank at the United States Naval Academy to investigate at which combinations of waves and current the net deforms and comes in contact with the sinker tube chain. A model in scale 1:40 was used to represent a fish cage with a circumference of 120 meters and net depth of 40 meters. Building a physical model of such a compliant structure is inherently difficult, so particular attention was given to similarity issues. With the physical modelling approach, two different net design and four different weighting systems were tested. The experiments showed that the sinker tube with the fixed connection to the net performs better than individual weights both for cylindrical and conical nets. For cylindrical nets exposed to current only contact occurred at a velocity of 0.3 m/s when using weights and at a velocity of 0.5 m/s when using either the fixed or sliding sinker tube. The results for conical nets exposed to waves and current were less consistent. Weights (contact at 0.3 m/s) performed better than a sinker tube with sliding connection (contact due to waves only) but not as good as a fixed sinker tube (contact at 0.3 m/s). When exposed to waves and current contact occurred at a higher velocity and over a smaller area when using the conical net compared to the conventional cylindrical. For cylindrical nets contact occurred when exposed to waves alone, whereas for conical nets contact occurred at current velocities of 0 m/s, 0.15 m/s, and 0.3 m/s for the weights, the sliding sinker tube, and the fixed sinker tube respectively.

Composition, seasonality and distribution of the Ichthyoplankton in the Lower Swan Estuary, South-western Australia

Paired conical nets (0.5 mm mesh) were used to sample ichthyoplankton at three sites in the lower Swan Estuary in each month between May 1986 and April 1987. In all, 3948 fish larvae were caught, representing 32 families and 60 species, of which 29 could be assigned species names. The Clupeidae (20.2%), Engraulididae (10.4%), Callionymidae (8.7%) and Nemipteridae (6.8%) made the greatest contributions to the total larval number, followed by the Pinguepididae (5.8%), Gobiidae (5.8%), Terapontidae (5.7%) and Monacanthidae (5.4%). The most numerous of the identified species were Engraulis australis (10.4%), Hyperlophus vittatus (8.9%), Callionymus goodladi (8.7%) and Sardinella lemuru (7.4%). The 11 most abundant of the identified species included 2 that spawn in the estuary (E. australis and Parablennius tasmanianus) and 2 that spawn at sea but are abundant as juveniles in the estuary (Pelates sexlineatus and H. vittatus). The remaining 7 species are not common as either juveniles or adults in any region of the Swan Estuary. The larvae of marine species collected just inside the estuary mouth were very similar in size to those collected a further 7.2 km upstream, indicating that they are transported rapidly through the lower estuary, presumably through tidal action. The concentrations of both eggs and larvae of all fish collectively, and the concentrations of larvae of most of the abundant identified species, peaked between late spring and midsummer (November- January).

ZOOPLANKTONIC ASSOCIATIONS, THROPHIC RELATIONS AND STANDING STOCK OF KRILL AND OTHER GROUPS OF THE COMMUNITY NEAR ELEPHANT ISLAND (FEBRUARY - MARCH 84/85)

Plankton samples were taken near Elephant Island on two oceanographic cruises of “NApOc Barão de Teffé” during the 2nd and 3rd Brazilian Antarctic Expeditions in February-March 1984 and 1985. Oblique hauls were performed with 325 /xm conical nets provided with calibrated flowmeters. Identification of species of zooplankton and phytoplankton of the stomach contents was made and distribution and abudance of zooplanktonic species were studied. Salps pellets were analysed too. The population structure of Euphausiacea of the two cruises was analysed and compared. During February-March 1984 a characteristic zooplanktonic association was found named "Salpidae Water” composed by Salpidae, the dominant group, Euphausiacea, Amphipoda and species of big Copepoda. The krill standing stock was very low and only furcilias V, VI, juveniles, subadults and adults were found. The high number of Salpidae changed the common composition of the antarctic zooplanktonic community excluding small filter — feeding species and allowing the survival of another of big size and carnivorous. The specific composition of samples obtained in February-March 1985 was different showing a drastic diminution of Salpidae and the occurrence of Copepoda populations, species and larvae of small size. The krill standing stock was higher than 1984 and the populations were represented by all larval stages occurred in small numbers.All these differences and variations are discussed. Based on the results of the study of the stomach contents and of the salp pellets and on the data of the other authors a trophic relations outline of the zooplankton community is given. Associações zooplanctônicas, relações tróficas e standing stock do krill e outros grupos da comunidade próximo à Ilha Elefante (Fevereiro — Março 84/85).Durante as 2a e 3a Expedições Brasileiras à Antártica realizadas pelo “NApOc Barão de Teffé” durante os meses de fevereiro e março de 1984 e 1985, foram efetuadas coletas de zooplâncton ao redor da Ilha Elefante. O material foi obtido mediante arrastos obliquos efetuados com redes cônicas de 325 um de abertura de malha, providas de fluxômetros calibrados. Foi identificado o zooplâncton a nível de espécie e seu conteúdo digestivo e os “ pellets” encontrados nas amostras. Foi estudada a distribuição e abundância de cada uma das espécies e foi analisada e comparada a estrutura das populações de Euphausiacea nos dois cruzeiros. Durante a período fevereiro/março de 1984 foi encontrada uma associação característica denominada "Água de Salpas” composta por Salpidae, Euphausiacea, Amphipoda e espécies de grande porte de Copepoda. O "standing stock” de krill apresentou valores muito baixos e as populações estiveram representadas somente por furcilias V, VI, juveniles, subadultos e adultos. A dominância de Salpidae modificou, o que poderia ser chamada de composição comum da comunidade zooplanctônica, excluindo espécies filtradoras pequenas e permitindo a sobrevivência de espécies de maior porte e de carnívoros. A composição específica das amostras obtidas durante o período fevereiro/março de 1985 modificou-se apresentando uma drástica diminuição de Salpidae, o reaparecimento de populações de Copepoda e de espécies e larvas de pequeno tamanho. O “standing stock” de krill foi maior que o registrado no período de fevereiro/março de 1984 e as populações estiveram compostas por indivíduos de todos os estádios larvais a partir de Caliptopis I e ao contrário da campanha anterior, juvenis, subadultos encontram-se em menor número.Todas estas diferenças e variações são discutidas. Em base nos dados obtidos do conteúdo estomacal das espécies zooplanctônicas, dos “pellets” das Salpas e dados de outros autores, é dado um esboço das relações tróficas da comunidade.

An automatic opening-closing device for large plankton nets and mid-water trawls

One of the most fundamental problems of oceanic ecology is the study of spatial and temporal changes in plankton distribution and the elucidation of the factors that govern them. A prerequisite of such work is that the tech- niques of sampling should be of sufficient accuracy to allow real changes in distribution to be detected and expressed in quantitative terms. The difficul- ties of fulfilling these sampling requirements are formidable even for the smaller plankton organisms, but a number of reliable and accurate quantitative samplers do exist for animals in this size range. For the larger zooplankton and smaller nekton, however, the lack of suitable sampling gear and methods has to a great extent restricted our knowledge. While the use of large conical nets and trawls at all depths over a wide geographic range has produced a vast body of data on the systematics of the major groups of macroplankton, there is little precise data on the depth distribution of even the commonest forms and only the vaguest estimates are available as to their relative abundance. The lack of more precise data can be attributed to two major technical deficiencies, first, the absence of efficient and reliable methods by which large nets can be opened and closed at depth, and secondly, the lack of accurate depth monitoring equipment. This paper describes the preliminary results of work aimed at meeting the first of these requirements but reference will also be made to the use of an instrument that represents a major advance towards serving the second.

A Portable Mechanical Insect Trap

A trap for flying insects that incorporates some of the principles described by Williams and Milne (1935) and Chamberlin and Lawson (1910) was constructed. It consists basically of two conical nets that rotate in a horizontal plane around a central axis that is driven by an electric motor through a series of pulleys. The efficiency of the trap is not affected by wind as an increased airflow through one net is balanced by a decreased airflow through the other. It is green in colour to blend with its surroundings. The trap (Fig. 1) is 5½ feet high at the centre. It has three main sections (Fig. 2): the framework, the drivillg mechanism, and the nets.