Selectivity Curves Research Articles

Trammel net size-selectivity for Hipposcarus harid (Forsskål, 1775) and Lethrinus harak (Forsskål, 1775) in coral reef fisheries of Jeddah, Saudi Arabia

The present study estimated the size-selectivity of Hipposcarus harid and Lethrinus harak caught in monofilament trammel nets of 50, 56, and 62mm inner-panel mesh sizes. Fishing was carried out in the coral reef fisheries of Jeddah during the period from June 2013 to March 2014. The selectivity parameters were calculated using the SELECT method implemented in Pasgear 2 software. The normal location, normal scale, log-normal, gamma and bi-modal selectivity models were fitted to the data to estimate the selectivity curves. Results indicated that the log-normal model provided the best fit based on the lowest deviance value. Modal lengths estimated from the log-normal selectivity curves are: 19.73, 22.10, and 24.46cm for H. harid, 18.41, 20.62, and 22.83cm for L. harak caught with 50, 56 and 62mm inner-panel mesh sizes, respectively. The length–girth relationship was estimated and described by the linear equation: G=0.480+0.70L (r2=0.95) for H. harid, and G=0.73L−0.65 (r2=0.96) for L. harak. For proper management of H. harid and L. harak, the minimum inner-panel mesh size should be 62mm to catch fish sizes larger than the length at maturity for both species.

Codend selectivity in a commercial Danish anchor seine

Danish seining (or anchor seining) is a fishing technique that is gaining increasing attention because it is considered to be a fuel-efficient fishing method with low environmental impact. However, scientific documentation of the selectivity characteristics of Danish seines is lacking, and the gear generally is grouped with bottom trawls and Scottish seines in fisheries management legislation. In this study, we developed a codend cover to estimate the selectivity of a standard commercial Danish seine codend for four fish species. The data for the dominant species, dab (Limanda limanda) and plaice (Pleuronectes platessa), was best described by models that combine two or three logistic models, which indicated that more than one selection process was at work. Selectivity of cod (Gadus morhua) was best described by a Richard curve and selectivity of red gurnard (Chelidonichthys lucernus) by a logistic curve. The estimated selectivity curve of dab indicated, contrary to cod and plaice, low retention of individuals below MLS. Confidence limits for larger length classes of cod and red gurnard were relatively wide. For plaice, the estimated selection factor, which is the length with 50% retention divided by mesh size, was comparable to literature values from trawl studies. The average value for cod was similar for Danish and Scottish seines, but lower for trawls. The results are discussed in the context of fisheries management with focus on the landing obligation of the new Common Fisheries Policy.

Effects of the geometry of fine powder outlet on pressure drop and separation performances for dynamic separators

The performance of a dynamic separator installed in the cement industry with different conceptions of fine collection outlets, was evaluated using the FLUENT software. One cylinder shaped and four tangential shaped fine exit tubes were designed to compare the behavior of the flow field of various geometries of air classifiers. Turbulence closure is affected by employing the Reynolds Stress Model which takes into consideration the effects of swirl, rotation and high complex three-dimensional flows. The discrete phase model was used to predict the effect of the geometry of the outlet on the collection efficiency and the fish-hook effect. It is found that the modified structure have a great impact on the velocity and pressure fields. The simulation results indicate that the tangential and the axial velocities are hardly influenced by the modified structure of the fine powder geometry. The findings also suggest that the large radial velocity gradients in the axial region as well as in the areas between the rotor blades would cause the return of the fine particles to the annular region to be mixed again with the coarse powder. This phenomenon is more marked for the A type of the separator and leads to a higher fish-hook effect in the selectivity curve. But in simulation, reducing the number of the fine powder exits can decrease greatly the computing memory and time.

Spin/orbital and magnetic quantum number selective magnetization measurements for CoFeB/MgO multilayer films

Spin selective magnetic hysteresis (SSMH) curves, orbital selective magnetic hysteresis (OSMH) curves and magnetic quantum number selective SSMH curves are obtained for CoFeB/MgO multilayer films by combining magnetic Compton profile measurements and superconducting quantum interference device (SQUID) magnetometer measurements. Although the SQUID magnetometer measurements do not show perpendicular magnetic anisotropy (PMA) in the CoFeB/MgO multilayer film, PMA behavior is observed in the OSMH and SSMH curves for the |m| = 2 magnetic quantum number states. These facts indicate that magnetization switching behavior is dominated by the orbital magnetization of the |m| = 2 magnetic quantum number states.

Selectivity of multifilament trammel and gillnets for common carp (Cyprinus carpio L., 1758) in Lake Marmara

This study was aimed to estimate the selectivity properties of multifilament trammel and gillnets for common carp ( Cyprinus carpio L., 1758) in Marmara Lake in Manisa, Turkey. Trammel and gillnets of 4, 6, 8, and 10 cm stretched mesh size and 210 d/2 no twine thickness were tested in the Marmara Lake. In addition, selectivity parameter of 11, 12, 13 and 14 cm mesh size of trammel and gillnets were modelled. SELECT method was used to estimate the selectivity parameters. Experiments were carried out monthly in the three different stations identified eastern, middle and western areas which represent longitudinal length of the lake. A total of 36 trials were conducted both nets. A total of 119 common carps were caught ranges between 11.3 - 49.0 cm total lengths. According to the Bi- normal model, which gave the lowest deviance for both trammel and gillnets, selectivity curves were estimated for 4, 6, 8, 10, 11, 12, 13 and 14 cm stretched mesh size modelled lengths as 12.98, 19.47, 25.96, 32.45, 35.70, 38.94, 42.19 and 45.43 cm for trammel nets, 12.40, 18.60, 24.80, 31.00, 34.10, 37.20, 40.30 and 43.40 cm for gillnets, respectively. When considering minimum landing size (40 cm total length), it is recommended that both nets under 13 cm mesh size should be prohibited for common carp fishery in the Lake Marmara. Keywords: Trammel net, gillnets, common carp Cyprinus carpio, size selectivity, Lake Marmara

Comparison of a rigid grid to a square-mesh panel in size selection for commercial fishing in the Persian Gulf shrimp trawl fishery

Two bycatch reduction devices (BRDs): a juvenile and trash fish excluder device (JTED) and a square-mesh panel (SMP), were tested in the Persian Gulf shrimp fishery from a small-scale shrimp trawler in October–November 2012. Each device was alternatively tested by using a small-mesh cover net to retain individuals that escaped the BRDs. Three valuable fish species—tigertooth croaker (Otolithes ruber), silver pomfret (Pampus argenteus) and silver sillago (Sillago sihama)—were selected for detailed analyses. Average escapement rates by number for commercial species in the trawl nets with either JTED or SMP were calculated as 24% and 33%, respectively. There were significant differences in escapement rates for Otolithes ruber and Sillago sihama between JTED and SMP (p < .05). In both BRDs, Pampus argenteus had the smallest escapement rate. A two-sample Kolmogorov–Smirnov test detected a significant difference (p < .05) in the length-frequency of Sillago sihama, and Otolithes ruber captured in the codend and cover net equipped with JTED. Selectivity curves of both BRDs indicated that for each species, the length of 50% retention probability (L50) was substantially smaller than the length at maturity (Lm), except for Otolithes ruber. From an ecological perspective, the codend equipped with SMP was superior to the codend equipped with JTED because it retained substantially fewer under-sized fish and had the smallest selection range. It therefore seems that replacing the standard codend with a codend equipped with SMP provides the best outcome for the fishery whereby fishermen will increase their catches of larger fish while simultaneously reducing their under-sized fish catches.

Humidity and temperature induced changes in the diffraction efficiency and the Bragg angle of slanted photopolymer-based holographic gratings

This work explores the humidity and temperature response of volume phase slanted gratings recorded in photopolymers with varied chemical composition. Acrylamide and diacetone acrylamide were used as monomers and triethanolamine and N-phenylglycine were used as photoinitiators. The study demonstrates that the response of photopolymer-based holographic gratings to relative humidity (RH) and temperature (T) can be tuned by alteration of the photopolymer composition.Humidity and temperature response of the holograms has been characterized by recording Bragg selectivity curves of transmission gratings and by monitoring the position of the maximum intensity in the spectral response of reflection gratings. Investigation of the humidity response in the range of 20–90% RH reveals that photopolymers containing triethanolamine are more responsive to moisture than photopolymers containing N-phenylglycine and display significant sensitivity to relative humidity above 40%. Full reversibility of humidity induced changes in gratings recorded in diacetone acrylamide-based photopolymer is confirmed at RH≤60%. Exposure to RH≥70% leads to irreversible changes in these gratings.The temperature response of slanted transmission gratings was investigated in the temperature range of 20–60°C. Exposure of the photopolymer layers containing triethanolamine to elevated temperature was found to cause layer shrinkage due to desorption of absorbed water. Sealed layers containing triethanolamine, however, demonstrated swelling due to the effect of thermal expansion. The photopolymer layers containing N-phenylglycine were found to be unresponsive to temperature changes below 30°C and have sensitivity to temperature above 30°C.

Is the survey selectivity curve for Pacific cod (Gadus macrocephalus) dome-shaped? Direct evidence from trawl studies: suppl. text

Is the survey selectivity curve for Pacific cod (Gadus macrocephalus) dome-shaped? Direct evidence from trawl studies: suppl. text

Is the survey selectivity curve for Pacific cod (Gadus macrocephalus) dome-shaped? Direct evidence from trawl studies

Is the survey selectivity curve for Pacific cod (Gadus macrocephalus) dome-shaped? Direct evidence from trawl studies

Longline selectivity for white-spotted conger Conger myriaster (Brevoort, 1856) in Haizhou Bay, China

Conger myriaster is one of the most commercially important fish stocks in the Haizhou Bay, China. As the type of longline fishing hook has a significant effect on its capture, three hook sizes (nos. 302, 303, 304) were compared in experiments conducted along the Haizhou Bay from September to November 2012. C. myriaster selectivity analysis using the different hook widths was obtained by analysing the catch rate, CPUE, total length distribution and selection curves. The log-normal model equation was used to explore the longline selection, and anova was employed to analyse the difference in catch rate and CPUE among the three hook sizes. The longline selectivity for C. myriaster was well described by a log-normal model equation. Hook no. 303 proved to have the highest catch rate, CPUE, and the estimated model lengths within three types of hooks tested in the experiments, in accordance with the fact that no. 303 is also the favourite hook used by local fishermen. Overall, the present study indicates that hook no. 303 has the best selection and is an appropriate size for sustainable utilisation of C. myriaster.

Narrowing of the emission spectra of high-power laser diodes with a volume Bragg grating recorded in photo-thermo-refractive glass

The spectral characteristics of a high-power semiconductor laser with an external cavity in which longitudinal-mode selection is implemented by means of a holographic volume Bragg grating recorded in photo-thermo-refractive glass are investigated. Mode selection leads to narrowing of the spectrum of the laser diode from an initial width of 6 nm to 5 A. In the narrowed spectrum, a fine structure representing a set of eigenmodes that correspond to the length of a laser chip is resolved. The number of these modes is limited by the width of the spectral selectivity curve of the grating. It is shown that insertion of the grating into the cavity leads to severalfold enhancement of the grating selectivity. It is demonstrated that the implemented external-cavity design makes it possible to smoothly tune the laser emission wavelength in a 10-nm range.

Length Selectivity and Size‐Bias Correction for the North American Standard Gill Net

AbstractGill nets are inherently size selective, but selectivity curves can correct this bias. We sampled eight reservoirs with the North American standard gill net to develop a large length‐specific data set for six species: Channel Catfish Ictalurus punctatus, hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis), saugeye (Sauger Sander canadensis × Walleye S. vitreus), Walleye, White Bass, and White Crappie Pomoxis annularis. We then used the SELECT (share each lengthclass's catch total) method to find the best‐fit selectivity model to adjust the gill‐net catch for contact selectivity. To determine the magnitude of these selectivity corrections, we compared adjusted and unadjusted length frequencies and size indices for each species at each reservoir. The bimodal model was the best fit selectivity model for all species. When selectivity‐adjusted length‐frequency data were compared with the original data, one‐third of hybrid Striped Bass length frequencies and two‐thirds of White Bass length frequencies were significantly different (unadjusted distributions underestimated smaller length classes). Roughly one‐third of the proportional size distributions (PSDs) from all species analyzed showed meaningful changes (≥5 PSD units) after selectivity adjustments were made (unadjusted PSDs were too large). By correcting for contact selectivity the data are improved, and at times the adjustments can be large enough to alter management decisions. Therefore, we recommend that selectivity adjustments should become a part of routine data analysis for the design of the North American standardized gill net as this will improve data for fisheries management.Received September 1, 2015; accepted December 21, 2015 Published online May 16, 2016

Risk Analysis of Plausible Incidental Exploitation Rates for the Pacific Sleeper Shark, a Data‐Poor Species in the Gulf of Alaska

AbstractMonte Carlo simulation was used to investigate the sustainability of incidental exploitation rates (U) for Pacific Sleeper Sharks Somniosus pacificus in the Gulf of Alaska (GOA) under status quo management. Monte Carlo simulations were implemented with a standard, length‐based, age‐structured model that was evaluated with forward projection. Given the paucity of relevant data, we investigated the sensitivity of simulation results to a range of assumptions about key model parameters by using 24 alternative model configurations, each simulated 1,000 times. The risk analysis results were most sensitive to Pacific Sleeper Shark U‐values. The aggregate fraction of simulations ending in an overfished condition increased from 0% under the low‐U scenario to 59% under the high‐U scenario. Risk analysis results were also sensitive to the assumed shape of the length‐based selectivity curve (asymptotic or dome shaped) but were less sensitive to the range of assumptions about other key model parameters, including maximum age and stock productivity. These results indicate that a priority for Pacific Sleeper Shark management is to reduce the uncertainty in U. This major uncertainty will be decreased by an observer program that is now in place to monitor the historically unobserved GOA Pacific Halibut Hippoglossus stenolepis fishery, which incidentally catches Pacific Sleeper Sharks.Received March 19, 2015; accepted December 7, 2015 Published online May 16, 2016

Bell-shaped size selection in a bottom trawl: A case study for Nephrops directed fishery with reduced catches of cod.

Monotonous size selection curves have traditionally been sufficient to describe the size selection in the aft end of a bottom trawl. Such modelling is a good approximation when the size selective system consists of a single selective device. However, in some fisheries the demands for species and size selectivity have motivated the development of selective systems in trawl fisheries that utilize more than one selective device simultaneously. An example can be found in the Swedish demersal trawl fishery targeting Norway lobster (Nephrops norvegicus), which simultaneously aims at avoiding catches of Atlantic cod (Gadhus morhua). In this fishery, the selective system consists of a Nordmøre type sorting grid followed by a size selective square mesh codend. The size selection curve for this system has a characteristic bell-shaped curvature, which cannot be sufficiently described by a monotonous selection curve. An approach that can handle a bell shaped curvature is to use a more flexible empirical size selection model. However, such models primarily use a curve fitting procedure, and do not allow the possibility to investigate the contribution of the individual parts of the selection system. Therefore, we choose to use a structural-based model that directly models the contributions of the individual selectivity devices to the overall performance of the system. We demonstrate that this approach can appropriately describe the experimental size selection data for both Nephrops and cod in a system composed of a sorting grid followed by a size selective codend. Furthermore, this approach provides a direct quantification of the selective processes of the individual parts of the system to the overall size selection in the fishing gear. In addition, we demonstrate how this approach can provide fisheries managers with a new tool when trying to develop more sustainable fisheries through improving fishing gear size and species selectivity.

Selectivity curves of the capture of mangrove crab (Ucides cordatus) on the northern coast of Brazil using bayesian inference.

Fishing selectivity of the mangrove crab Ucides cordatus in the north coast of Brazil can be defined as the fisherman's ability to capture and select individuals from a certain size or sex (or a combination of these factors) which suggests an empirical selectivity. Considering this hypothesis, we calculated the selectivity curves for males and females crabs using the logit function of the logistic model in the formulation. The Bayesian inference consisted of obtaining the posterior distribution by applying the Markov chain Monte Carlo (MCMC) method to software R using the OpenBUGS, BRugs, and R2WinBUGS libraries. The estimated results of width average carapace selection for males and females compared with previous studies reporting the average width of the carapace of sexual maturity allow us to confirm the hypothesis that most mature individuals do not suffer from fishing pressure; thus, ensuring their sustainability.

Effect of twine thickness on size-selectivity of driftnet for the yellow croaker Larimichthys polyactis in southwestern Sea of Korea

In order to determine the effect of twine thickness on the size-selectivity of the driftnet used for the yellow croaker, size-selectivity tests were conducted with three different twine thicknesses (monofilament diameters of 0.279 mm (number’s method; No. 3), 0.321 mm (No. 4), and 0.360 mm (No. 5)) of driftnets for the yellow croaker in the seas around Chooja-do, Jeju Islands. The selectivity curve was estimated by using Kitahara’s method. In order to determine the physical properties of the twine used in the experimental fishing nets, we measured the breaking load, elongation, and stiffness under both dry and wet conditions. In terms of physical properties, the thinnest twine (No. 3) had the strongest breaking strength per unit cross-sectional area, along with good elongation and excellent flexibility. The thickest twine (No. 5) had the lowest flexibility. In terms of selectivity, the net of No. 3 twine showed the broadest selection range and, thus, a relatively low selectivity compared with the other nets, while the less flexible net of No. 5 twine showed the narrowest selectivity range and high selectivity. In addition, it was found that a thicker twine resulted in a smaller haul of small fish. Therefore, it can be inferred that the thickness of the twine affects the size of the catch and selectivity, and thus the size composition of the catch as well.

CHARACTERIZING DUST ATTENUATION IN LOCAL STAR-FORMING GALAXIES: UV AND OPTICAL REDDENING

ABSTRACT The dust attenuation for a sample of ∼10,000 local (z ≲ 0.1) star-forming galaxies is constrained as a function of their physical properties. We utilize aperture-matched multiwavelength data available from the Galaxy Evolution Explorer and the Sloan Digital Sky Survey to ensure that regions of comparable size in each galaxy are being analyzed. We follow the method of Calzetti et al. and characterize the dust attenuation through the UV power-law index, β, and the dust optical depth, which is quantified using the difference in Balmer emission line optical depth, &tau; B l = &tau; H &beta; &minus; &tau; H &agr; ?> . The observed linear relationship between β and &tau; B l ?> is similar to the local starburst relation, but the large scatter (σ int = 0.44) suggests that there is significant variation in the local universe. We derive a selective attenuation curve over the range 1250 Å &lt; λ &lt; 8320 Å and find that a single attenuation curve is effective for characterizing the majority of galaxies in our sample. This curve has a slightly lower selective attenuation in the UV compared to previously determined curves. We do not see evidence to suggest that a 2175 Å feature is significant in the average attenuation curve. Significant positive correlations are seen between the amount of UV and optical reddening and galaxy metallicity, mass, star formation rate (SFR), and SFR surface density. This provides a potential tool for gauging attenuation where the stellar population is unresolved, such as at high z.

Flotation of rare earth minerals from silicate–hematite ore using tall oil fatty acid collector

The flotation of rare earth (RE) minerals (i.e. xenotime, monazite-(Nd), RE carbonate mineral) from an ore consisting mainly of silicate minerals (i.e. primary silicate minerals and nontronite clay) and hematite was investigated using tall oil fatty acids (Aero 704, Sylfat FA2) as collector. The RE minerals are enriched with Fe. The effects of tall oil fatty acid dosage, pH, temperature, and conventional depressants (sodium lignin sulfonate, sodium metasilicate, sodium fluoride, sodium metasilicate and sodium fluoride, and soluble starch) were determined at grinding size of P80=63μm. At this grinding size, the grain size of the RE minerals ranges from 2 to 40μm, percentage liberation is 9–22%, and percentage association with nontronite and quartz is 30–35%. Results indicated that Sylfat FA2 at 22450g/t concentration was the more efficient tall oil fatty acid collector at natural pH (pH 7) to basic pH (pH 10.0–11.5). Flotation at the room temperature (25°C) gave higher selectivity than 40°C temperature flotation. The results on the effect of depressants showed similar selectivity curves against the gangues SiO2, Al2O3, and Fe2O3 suggesting that the chemical selectivity of the depressants has been limited by the incomplete liberation of the RE minerals in the feed sample. High recoveries at 76–84% (Y+Nd+Ce)2O3 but still low (Y+Nd+Ce)2O3 grade at 2.1% in the froth were obtained at flotation conditions of 63μm, 25°C, pH 10.5, 1,875g/ton sodium metasilicate and 525g/ton sodium fluoride or 250g/ton soluble starch as depressant for the silicates and hematite, and 22,450g/t Sylfat FA2 as collector for the RE minerals (initial (Y+Nd+Ce)2O3 feed grade=0.77%). The recoveries of gangue SiO2, Al2O3, and Fe2O3 in the froth were low at 25–30%, 30–37%, and 30–36%, respectively. The mineralogical analysis of a high grade froth and its corresponding tailing product showed that the RE minerals have been concentrated in the froth while the primary silicate minerals and hematite have been relatively concentrated in the tailing. However, the clay minerals, primary silicate minerals, and hematite still occupy the bulk content of the froth. This suggests that incomplete liberation of the RE minerals led to the poor grade result, supporting likewise the selectivity curve results by the different depressants. This study showed that liberation is important in achieving selective separation.

Selectivity of commercial and experimental codends for the demersal trawl fishery of the deep-water rose shrimp, Parapenaeus longirostris (Lucas, 1846), in the Aegean Sea

In this study, the selectivity of commercial and alternative (experimental) codends for the deep-water rose shrimp, Parapenaeus longirostris, in the Aegean Sea demersal trawl fishery was investigated. Tested were the 44-mm diamond mesh codend as used in commercial fisheries (D44), in addition to a 50 mm diamond (D50), a 40 mm square (S40), and a 40 mm 90° turned mesh (T40), respectively. Sea trials were carried out in the eastern Aegean Sea, with a local commercial trawler using a modified trawl net with 620 meshes circular mouth opening. A total of 35 valid daytime hauls (8 with D44, 9 with D50, 8 with S40 and 10 with T40) were carried out. Selectivity data were collected using the covered codend method and analysed by means of a logistic equation with the maximum-likelihood method. Mean selection curves were estimated and compared using the between-haul variations model. The mean 50% retention carapace length values (LC50) were estimated as 21.2 ± 0.1, 23.2 ± 0.3, 20.8 ± 0.2 and 20.5 ± 0.4 mm CL for D44, D50, S40, and T40, respectively. Selection range (SR) values were determined as 4.9 ± 0.1 mm in D44, 8.7 ± 0.3 mm in D50, 4.0 ± 0.3 mm in S40, and 10.1 ± 0.3 mm in T40. While haul duration and total catch among the parameters did not affect the LC50 values for the investigated codends, the value of the parameter describing the weight of P. longirostris caught in that codend showed an effect for the D50 and T40 codends. Consequently, all investigated codends yielded sufficient LC50 results when considering the minimum landing size (MLS) value imposed by the EU (20 mm CL). In conclusion, the legally allowed S40, which gave an LC50 value close to that of D44, and which would be the preferable codend in terms of its releasing characteristics for individuals under the MLS value (89%), can be used as a good alternative for the D44 (preferred by the fishermen) in the deep-water rose shrimp fishery.

Understanding and Predicting Size Selection in Diamond‐Mesh Cod Ends for Danish Seining: A Study Based on Sea Trials and Computer Simulations

AbstractDanish seining is an important fishing method used to harvest demersal species. Knowledge about the size selectivity of different demersal species with this type of fishing gear is therefore of importance for managing the exploitation of marine resources. However, there are only limited data on size selection in cod ends in this fishery. Sea trials were therefore carried out to collect size selectivity data for Atlantic Cod Gadus morhua, Haddock Melanogrammus aeglefinus, and Witch Flounder Glyptocephalus cynoglossus for a diamond‐mesh cod end. For all three species, the data were best described by a double logistic selection curve, implying that two different size selection processes occur in the cod end. The double selection process could be explained by an additional selection process occurring through slack meshes. The results imply that the escapement of 46% and 34% of the larger Atlantic Cod and Haddock (those above 48 cm), respectively, would be through wide‐open or slack meshes. Since these mesh states are only likely to be present in the latest stage of the fishing process (e.g., when the cod end is near the surface), a large fraction of the bigger fish probably escaped near the surface, which might influence their likelihood of survival. Furthermore, based on the models established for explaining the experimental size selection, we were able to predict the effect of changing the mesh size on cod end size selection in the Danish seine fishery.Received December 9, 2015; accepted February 18, 2016