Nets Of Different Mesh Sizes Research Articles

Size normalizing planktonic Foraminifera abundance in the water column

AbstractPlanktonic Foraminifera have been collected from the water column with different plankton sampling devices equipped with nets of various mesh sizes, which impedes direct comparison of observed quantifications. Here, we use data on the community size structure of planktonic Foraminifera to assess the impact of mesh size on the measured abundance (ind m−3) of planktonic Foraminifera. We use data from the FORCIS database (Chaabane et al., 2023, Scientific Data 10: 354) on the global ocean at different sampling depths over the past century. We find a global cumulative increase in abundance with size, which is best described using a Michaelis–Menten function. This function yields multiplication factors by which one size fraction can be normalized to any other size fraction equal to or larger than 100 μm. The resulting size normalization model is calibrated over a range of different depth intervals, and validated with an independent dataset from various depth ranges. The comparison to Berger's (1969, Deep. Res. Oceanogr. Abstr. 16: 1–24) equivalent catch approach shows a significant increase in the predictive skill of the model. The new size normalization scheme enables comparison of Foraminifera abundance data sampled with plankton nets of different mesh sizes, such as compiled in the FORCIS database. The correction methodology may be effectively employed for various other plankton groups such as diatoms and dinoflagellates.

Morphology, Age and Growth of Bunni, Barbus sharpeyi Gunther, 1874 in Swab marsh, south Iraq

Morphology, age and growth of Bunni, Barbus sharpeyi Gunther, 1874 in Swab marsh, south Iraq, was studied from December 2004 to November 2005. A total of 864 B. sharpeyi (100-533mm TL) were collected using gill nets of different mesh sizes and electrical fishing. Twenty one morphometric and seven meristic characters for the species were described in the study. The morphometric characters were calculated as numerical ratio to standard and head lengths. The indices characters associated with standard length ranged from 0.0043 of eye diameter to 1.22 of total length, and with head length ranged from 0.178 of eye diameter to 0.752 of head width. The slopes of the regression lines ranged from 0.023 of eye diameter to 1.142 of total length. Fishes of 200-360mm length groups of B. sharpeyi were dominants in the samples. Total length–weight relationship of B. sharpeyi was W= 3.839 × 10-6 L 3.2017. The mean relation condition factor was 1.001. The annuli on scales formed during December and the growth of the scales was high during the period from February to August and was associated with water temperatures. The relation between standard length (L) and scale radius (S) was: L = 17.737 + 5.0469 S. The age composition ranged from 1 to 7. The standard lengths for these ages were 138.0, 202.0, 248.0, 304.8, 353.8, 393.1 and 439.2mm respectively. The growth of B. sharpeyi in Swab marsh was better than that of at Iraqi waters with the exception of B. sharpeyi at Hammar marsh. The mathematical model of growth as calculated by von Bertalanffy equation was Lt = 650 [1-e -0.138 (t + 0.642)].

Growing cabbage (Brassica oleraceae var. capitata) under low cover Agronets prevents pest infestation and increases yields in Kenya

Cabbage (Brassica oleracea var. capitata) is an important vegetable crop in Kenya both in production and income provision to smallholder farmers. Pests are serious hindrance to its production and most farmers rely on synthetic insecticides. Such reliance has negative effects on non-target organisms, environment, animal and human health. This study was carried out from May to October 2011 to determine impact of low cover nets of different mesh size and cover duration on reducing cabbage pest infestation and yields. The study was conducted at Kenya Agricultural Research Institute Kabete and Practical Training Centre Thika based on a randomized complete block design with five replicates. Treatments included Agronets of fine (0.4mm) and large (0.9mm) mesh covered over the crop permanently (season-long) or temporarily (opened three times a week from 9am to 3pm) and control where no Agronet was used. The results show that the number and damage by diamondback moth (DBM) was significantly lower on cabbages grown under the Agronets compared with control. Infestation by thrips was lower on cabbages grown under permanent cover compared with those under temporal cover and without cover. However, there was no significant difference of aphids infestation. The marketable yield was significantly higher on cabbages grown under the Agronets, recording about 17% yield loss compared with control that recorded about 90% yield loss. The study concludes that Agronets provide an important component of integrated pest management strategy for cabbage production in Kenya with high crop yields benefit and highly recommended for application by growers. Key words: Agronet, Aphids, Cabbage, Diamondback moth, Thrips

Nylon nets: a simple pest exclusion barrier technique to manage rhinoceros beetle menace in coconut plantations

Oryctes rhinoceros (L.) is a major pest of palms worldwide. Seedlings and juvenile palms are more vulnerable to beetle damage and in severe cases, inflicting palm death. The present study was to develop a physical pest control technique for juvenile palms using nylon nets as a pest exclusion barrier. The unopened spear leaf with –two to four adjacent leaf bases were loosely wrapped with the nylon nets of different mesh size during June - December 2017 (N = 40). Results revealed that the damaged leaves were reduced from 61.02 to 7.53% (t = 17.23; p < 0.001). Further experiment was up scaled in 120 palms during June – December 2018 and the beetles trapped in nylon nets were recorded at weekly intervals. Nylon nets entrapped 618 adult beetles that comprised 61.80% females and 38.18% males with corresponding sex ratio of 1.61: 1. Thus, use of nylon nets as a pest exclusion barrier guarded the young palms from beetle attack and additionally acted as passive trap by entrapping 20.6 beetles/week/120 palms without any insecticidal intervention.

Diversity of Freshwater Fish in Fragmented Forest of Wilmar Oil Palm Plantation, Miri, Sarawak

The study was conducted in the river system located at Wilmar oil palm plantation in Miri, Sarawak. The objective of the study is to determine the fish species diversity and composition in the streams and rivers in the oil palm plantations. Fish were sampled using a variety of fishing methods, including, scoop nets, cast net, and gill nets of different mesh sizes (1.0, 1.5, 2.0, 2.5, 3.75 and 4.0 cm) from 2 to 7 of February 2014. A total of 326 individual fish including 32 species of native fishes and one species of non-native fish from 19 genera, seven families and five orders were collected from seven locations. The cyprinid fish represented 62.20% of the total fish caught and was found in all the rivers surveyed. About six endemic species in Borneo such as Barbonymus collingwoodii, Barbodes banksi, Barbodes sealei, Hampala bimaculata Nematabramis borneensis and Nematabramis everetti were identified. However, only one species from families Bagridae, Balitoridae, Clariidae, and Hemiramphidae was sampled from the study sites. The higher fish species composition found in streams and rivers of the oil palm plantation landscapes could be attributed to the conservation of some areas of the plantation as high conservation value forest (HCVF) status, which have provided suitable habitat for fish species within the plantation aquatic environments.

Relationships between environmental conditions and fish assemblages in the Lohore River of Dailekh, Western Nepal

The Lohore River is one of the important riverine ecosystems of Dailekh which support diverse aquatic communities. The present study was carried out to assess the fish diversity status with relation to environmental conditions in both to space and time. The survey was conducted at three different sampling stations in three different seasons. For the fish sampling, two cast nets of different mesh sizes were used, one having large mesh size of 2 cm, 6 m diameter and 6 kg weight and another having mesh size of 0.5 cm, 3 m diameter and 2 kg weight. Moreover, drag net and gill net were also used to collect the fish samples. A total of 11 fish species belonging to 2 orders, 3 families and 7 genera. Results from the similarity percentage analysis (SIMPER) suggested that fish species of Puntius gelius, Schizothorax plagiostomus, Tor chelynoides and Schistura sovana were major contributing species each contribute more than 9%. An analysis of similarity (ANOSIM) pointed that fish community structure in the Lohore River differ in spatial scale (p&lt;0.01) but not in temporal scale (P&gt;0.01). Water temperature, dissolved oxygen and water velocity was found as influential factors for fish species distribution.

Are we underestimating microplastic abundance in the marine environment? A comparison of microplastic capture with nets of different mesh-size

Microplastic debris is ubiquitous and yet sampling, classifying and enumerating this prolific pollutant in marine waters has proven challenging. Typically, waterborne microplastic sampling is undertaken using nets with a 333 μm mesh, which cannot account for smaller debris. In this study, we provide an estimate of the extent to which microplastic concentrations are underestimated with traditional sampling. Our efforts focus on coastal waters, where microplastics are predicted to have the greatest influence on marine life, on both sides of the North Atlantic Ocean. Microplastic debris was collected via surface trawls using 100, 333 and 500 μm nets. Our findings show that sampling using nets with a 100 μm mesh resulted in the collection of 2.5-fold and 10-fold greater microplastic concentrations compared with using 333 and 500 μm meshes respectively (P < 0.01). Based on the relationship between microplastic concentrations identified and extrapolation of our data using a power law, we estimate that microplastic concentrations could exceed 3700 microplastics m−3 if a net with a 1 μm mesh size is used. We further identified that use of finer nets resulted in the collection of significantly thinner and shorter microplastic fibres (P < 0.05). These results elucidate that estimates of marine microplastic concentrations could currently be underestimated.

Characteristics of root decomposition based on in situ experiments in a tropical rainforest in Sarawak, Malaysia: impacts of root diameter and soil biota

Tropical forests contribute significantly to the stability of global carbon (C) balance; however, little is known about root litter decomposition in tropical rainforests. In this study, we aimed to (1) characterise the effect of soil depth, root diameter and soil organisms on root litter decomposition and (2) estimate the contribution of root decomposition to soil carbon dioxide (CO2) efflux in a tropical rainforest in Malaysian Borneo. We incubated soil chambers with fine and coarse root litterbags at varying soil depths. Soil chambers were covered with nets of different mesh sizes, and CO2 efflux was monitored from the top of each soil chamber during the incubation. Our results showed that coarse roots decomposed faster than fine roots. There was no impact of soil depth, but soil animals and fungi had a significant impact on coarse root decomposition from 398 days after the start of the experiment. Soil CO2 efflux increased linearly with C loss from root decomposition, indicating that 40% of the CO2 efflux originates from root litter. The variation in root decomposition rates suggests the possible role of root litter in soil C storage and emission in a tropical rainforest.

Fish fauna of the Pelotas River, Upper Uruguay River, southern Brazil

Abstract: The fish fauna of the Pelotas River, in the Upper Uruguay ecoregion of southern Brazil was inventoried. Samplings were performed quarterly between August 2013 and May 2014 at 14 sites in the Pelotas River and its tributaries, using gill nets of different mesh sizes, sein nets, cast nets and electrofishing. In total, 7,745 specimens were recorded, comprising 46 species, belonging to 13 families and five orders. Approximately 80% of the species belonged to the orders Characiformes and Siluriformes, as well as the families Characidae and Loricariidae, which included a greater number of species. Of the total species, 24% were endemic to the Upper Uruguay River, four were identified only at the genus level and none was considered non-native. Approximately, half of the 98 species previously recorded for the Upper Uruguay basin were also detected in this study. The tributaries of the Pelotas River exhibited different faunas with five exclusive species. Thirty species were present in both the tributaries and the main channel. In addition, higher species richness, as well as the presence of larger-sized species were observed in the main channel. Many of the species not restricted to the Upper Uruguay River have already been reported as part of the Taquari-Antas River fauna. However, the local biodiversity of this region is under several threats, such as land use and installation of small hydroelectric plants. These results highlight the importance of the conservation of plateau/upland rivers, especially in the Upper Uruguay ecoregion, which shows a peculiar fish fauna and endemism.

A morphological and geometric method for estimating the selectivity of gill nets

We propose a new method for estimating gill net selectivity which estimates the probabilities leading to retention by analyzing both the fish morphology and the mesh geometry. This method estimates the number of fish approaching and contacting gill nets of different mesh sizes as an intermediate step towards computing the selectivity. Instead of assuming an underlying probability distribution as in indirect methods, we split the entire interaction between a fish and the gill net into several stages, each with its own probability. All the necessary parameters to compute these probabilities can be obtained from measurements of the fish, knowledge of the mesh geometry, and catch data from different mesh sizes. The framework offers three pathways for computing the total number of fish contacting the gill nets and has the capability to use both wedged and entangled fish in the analysis. As a proof of concept, the method is applied to catch data for cod (G. morhua) and Dolly Varden (S. malma) to estimate the number of fish contacting the gill nets in both cases. By estimating the number of fish contacting the gill net in addition to the selectivity, this method provides an important step towards deriving estimates of fish density in a particular fishery from gill net measurement.

Zooplankton structure in high latitude fjords with contrasting oceanography (Hornsund and Kongsfjorden, Spitsbergen)

Summary Zooplankton inhabiting the Hornsund and Kongsfjorden fjords on Spitsbergen (Svalbard) were investigated in summer 2013. The goal of the study was to determine how the zooplankton communities vary in environments functioning under different oceanographic regimes. Sampling was conducted with nets of different mesh size and selectivity (56 μm WP-2, 180 μm MultiNet, and 1000 μm Tucker Trawl), which permitted comparing a wide size spectrum of zooplankton components. Species composition did not differ substantially between the fjords, but the zooplankton in Hornsund was almost two times less numerous, and it had lower biomass per unit volume. The highest abundance at both sites was in the smallest zooplankton size fraction found only in samples taken with 56 μm mesh WP-2 net. These comprised as much as 71% and 58% of the total zooplankton abundance in Hornsund and Kongsfjorden, respectively. The communities in both fjords had comparable contributions of Arctic and boreo-Arctic species biomass in the year of the study. However, the comparison of zooplankton characteristics over several years showed changes in abundance and biogeographic structure that corresponded with variations in the physical environments of the fjords. The results of the study permit predicting the possible effects of the increasing influence of Atlantic waters on zooplankton communities inhabiting Arctic marine pelagic ecosystems.

Length-weight relationships of three freshwater cyprinid fish species from Chalakudy River, South Western Ghats, India

Summary This paper provides length-weight relationships (LWRs) for three freshwater cyprinid fish species: Barbodes carnaticus (Jerdon, 1849), Hypselobarbus kolus (Sykes, 1839) and Tor khudree (Sykes, 1839) from the Chalakduy River in South Western Ghats of India. Fish samples were collected on a monthly basis between April 2011 to March 2012 using gill nets of different mesh sizes (3.5–10 cm). LWRs for these three species had not been previously reported in FishBase.

Gymnocypris chuiTchang, Yueh &amp; Hwang, 1964 andGymnocypris scleracanthusTsao, Wu, Chen &amp; Zhu, 1992 from Lake Langcuo, Qinghai-Tibet Plateau

This study presents length-weight relationships (LWRs) for two sympatric species of the subfamily Schizothoracinae (Cyprinidae), Gymnocypris chui and G. scleracanthus, captured in Lake Langcuo in Tibet, China. A total of 193 specimens were collected in June and July of 2014 and 2015 using gill nets of different mesh sizes (mesh size: 2 × 2 cm, 3 × 3 cm). Specimens included 76 G. chui and 117 G. scleracanthus. The values of parameter b in the LWRs equations were estimated as 2.875 for G. chui, and 2.773 for G. scleracanthus, respectively. These are the first LWRs records for the two sympatric species.

Selective predators or choosy fishermen? Relation between fish harvest, prey availability and great cormorant (Phalacrocorax carbo sinensis) diet

The increase in numbers and range of the continental subspecies of great cormorant Phalacrocorax carbo sinensis in Europe has led to a growing number of conflicts with commercial fisheries and recreational angling. We investigated the dietary preferences (fish species and size classes) of wintering cormorants in two freshwater basins in Northern Italy, using pellet analysis and data on fish community composition. First, we compared cormorant diet (biomass of fish species consumed) with the annual harvest by professional fishing (biomass/year). Second, we compared diet with a measure of prey availability: direct fish sampling with nets of different mesh size. Cormorants preyed mainly on cyprinid fish. A comparison of pellet analysis and commercial fishing data showed that some fish species consumed by cormorants did not occur in the commercial harvest. Using only species that occurred in the diet and in the commercial harvest, there was no relationship between the amount of fish of different species taken. A positive correlation between pellet analysis data (consumed) and data from scientific fish sampling (available) showed that cormorants exploited fish resources on the basis of prey availability. Comparing the size of fish collected from nets and fish consumed by cormorants also showed that birds were selective with respect to prey size, picking mostly small individuals (< 110 g). We conclude that potential effects of cormorants on commercially important fish will mainly depend on habitat type (fish ponds, natural deep lakes, others), and that in the natural lakes in Lombardy cormorants mainly concentrate on species which are of limited value for commercial fishing.

Comparison of the effects of two bongo net mesh sizes on the estimation of abundance and size of Engraulidae eggs

Abstract Studies of ichthyoplankton retention by nets of different mesh sizes are important because they help in choosing a sampler when planning collection and the establishment of correction factors. These factors make it possible to compare studies performed with nets of different mesh sizes. In most studies of mesh retention of fish eggs, the taxonomic identification is done at the family level, resulting in the loss of detailed information. We separated Engraulidae eggs, obtained with 0.333 mm and 0.505 mm mesh bongo nets at 172 oceanographic stations in the southeastern Brazilian Bight, into four groups based on their morphometric characteristics. The difference in the abundance of eggs caught by the two nets was not significant for those groups with highest volume, types A and B, but in type C (Engraulis anchoita), the most eccentric, and in type D, of the smallest volume, the difference was significant. However, no significant difference was observed in the egg size sampled with each net for E. anchoita and type D, which exhibited higher abundance in the 0.333 mm mesh net and minor axis varying from 0.45-0.71 mm, smaller than the 0.505 mm mesh aperture and the mesh diagonal.

Spore Culture of Red Seaweed, Gloiopeltis furcata

AbstractTwo experiments were conducted to study Gloiopeltis furcata spore culture with different substrates in the nonreproduction season. Using spores discharged by fertile G. furcata frozen for storage, two experiments were conducted during the nonreproduction season. In the first experiment, G. furcata spores were collected and incubated in aquariums using palm line, polythene line, vinylon line, and three types of plastic sheets (white, ripple, and transparent polymethyl methacrylate) as substrates. In the second experiment, G. furcata spores were collected and incubated in a plastic tank using plastic sheets of different materials (PP, PE, and transparent PVC) and plastic even nets of different mesh sizes (3, 2, and 0.5 cm) as substrates. At the end of the experiment (after 60 d), discs with raised thallus were found on different plastic sheets and white plastic even nets, but no discs were visible on any type of line or on the black plastic even net (3‐cm mesh). The white plastic even net was found to be a suitable substrate for G. furcata spore culture in farms and for sporeling culture in sea. Results presented in this study are expected to aid in the progress of the artificial seeding of Gloiopeltis.

서해 꽃게 자망의 망목 선택성 연구

A series of fishing experiments were carried out in the western coastal waters of Korea from May, 2006 to September, 2007, using gill nets of different mesh sizes (m=101, 121.8, 152.5, 176.8, and 191 mm) to determine the mesh selectivity of gill net for swimming crab, Potunus trituberculatus. The catch species was composed of swimming crab (87%), Thomas's rapa whelk Rapana venosa (5%), arthritic neptune Neptunea cumingi (2%), Japanese swimming crab Charybdis japonica (2%), marbled sole Pleuronectes yokohamae (1%), pen shell Atrina pectinata, ocellate spot skate Okamejei kenojei, and so on. The carapace length (CL) of each swimming crab caught in the experimental nets was measured. Sponge crab (egg-bearing female crab) was appeared from the end of June to August in the coastal waters. The master selection curve was estimated by applying the extended Kitahara's method. The selection curve showed that the gill nets of larger mesh size allowed more crabs of small carapace size to escape. The optimum value (CL/m) was 0.645 and the CL/m was estimated to be 0.301, 0.354, 0.391, 0.422, and 0.450 when the retention probabilities were 0.1, 0.2, 0.3, 0.4 and 0.5, respectively.

Airflow attenuation and bed net utilization: observations from Africa and Asia.

Background/MethodsQualitative studies suggest that bed nets affect the thermal comfort of users. To understand and reduce this discomfort the effect of bed nets on temperature, humidity, and airflow was measured in rural homes in Asia and Africa, as well as in an experimental wind tunnel. Two investigators with architectural training selected 60 houses in The Gambia, Tanzania, Philippines, and Thailand. Data-loggers were used to measure indoor temperatures in hourly intervals over a 12 months period. In a subgroup of 20 houses airflow, temperature and humidity were measured at five-minute intervals for one night from 21.00 to 6.00 hrs inside and outside of bed nets using sensors and omni-directional thermo-anemometers. An investigator set up a bed net with a mesh size of 220 holes per inch2 in each study household and slept under the bed net to simulate a realistic environment. The attenuation of airflow caused by bed nets of different mesh sizes was also measured in an experimental wind tunnel.ResultsThe highest indoor temperatures (49.0 C) were measured in The Gambia. During the hottest months of the year the mean temperature at night (9 pm) was between 33.1 C (The Gambia) and 26.2 C (Thailand). The bed net attenuated the airflow from a minimum of 27% (Philippines) to a maximum of 71% (The Gambia). Overall the bed nets reduced airflow compared to un-attenuated airflow from 9 to 4 cm sec-1 or 52% (p < 0.001). In all sites, no statistically significant difference in temperature or humidity was detected between the inside and outside of the bed net. Wind tunnel experiments with 11 different mesh-sized bed nets showed an overall reduction in airflow of 64% (range 55 - 71%) compared to un-attenuated airflow. As expected, airflow decreased with increasing net mesh size. Nets with a mesh of 136 holes inch-2 reduced airflow by 55% (mean; range 51 - 73%). A denser net (200 holes inch-2) attenuated airflow by 59% (mean; range 56 - 74%).DiscussionDespite concerted efforts to increase the uptake of this intervention in many areas uptake remains poor. Bed nets reduce airflow, but have no influence on temperature and humidity. The discomfort associated with bed nets is likely to be most intolerable during the hottest and most humid period of the year, which frequently coincides with the peak of malaria vector densities and the force of pathogen transmission.ConclusionsThese observations suggest thermal discomfort is a factor limiting bed net use and open a range of architectural possibilities to overcome this limitation.

Some aspects of the ecology of mochokid species in river Ase, Southern Nigeria

Some ecological aspects of mochokid catfishes in River Ase, Southern Nigeria were studied for a period of two years (March 1982- February, 1984) using bottom-set drifting nets, surface-set drifting nets, cast nets, drag nets, and atalla lift nets of different mesh sizes. Fifteen species (15) accounting for 303 individuals and wet weight of 46,147.40g were captured. By number and weight, the fifteen species contributed to 7.17% and 13.30% of all total fishes caught respectively. Synodontis schall, Hemisyndontis membraceous and Synodontis budgetti were the prominent species. The monthly condition factors of all the 15 species ranged from 2.30 to 3.60 indicating well-being. Seventy two (72) individuals representing 12 species were captured between 0900 and 1200hrs. On seasonal basis, more fish species and individuals were caught during the rainy season than during the dry season. Apart from Synodontis omias, Synodontis violaceous and Synodontis courteti that were rare and represented by only one individual in some stations, all other species were heterogeneous among the five stations studied. Some ecological aspects of the mochokid species in River Ase have been discussed and compared to the findings of earlier studies carried out elsewhere.Key words: ecology, mochokids, Ase River, Nigeria

Study on the Adaptability Status and Reproductive Success of &lt;I&gt;Oreochromis niloticus&lt;/I&gt; L. (Pisces: Cichlidae) and Carp (&lt;I&gt;Cyprinus carpio&lt;/I&gt; L., 1758) in a Tropic Reservoir (Fincha, Ethiopia)

The adaptability status and reproductive success of the introduced fish Nile Tilapia ( Oreochromis niloticus L.) and common carp ( Cyprinus carpio L., 1758) in Fincha reservoir, Ethiopia were studied on monthly basis from July 2006 to August 2007. Gill nets of different mesh size (60 mm, 80 mm, 100 mm, 120 mm and 140 mm, stretched mesh size) and beich sein (50 m long) were used to harvest the fish (a total of 645 fishes). Total length (L) and body weight (W) of both species were measured to the nearest 0.1 cm and 1g respectively. The results of the study showed that both fish species are adapted and have established successful breeding population in the reservoir. The size at first sexual maturity (L 50 ) for Oreochromis niloticus in Fincha reservoir was 21.8 cm for female and 24.5 cm for the male while L 50 was 37.5cm and 24.5cm for female and male Cyprinus carpio respectively. It was found that Oreochromis niloticus breeds throughout the year showing a peak breeding season in January and July in Fincha reservoir while Cyprinus carpio showed a peak breeding season between March and June. The length-weight relationships, total length (L) in cm; total weight (W) in g were calculated for O. niloticus (W=0.8×10 -2 L 3.20 ; n=87; r 2 = 0.96) and C. carpio (W=1.4×10 -2 L 2.97 ; n=558; r 2 =0.99) and showed a curvilinear relationship signifying the fish grow nearly isometrically. A significant seasonal variation (ANOVA, P 0.05). Apparently, length frequency distribution of both species indicated that the fish population is normal fish population with no apparent problems of over exploitation.