scholarly journals Square-mesh codend circumference and selectivity

2009 ◽  
Vol 66 (3) ◽  
pp. 566-572 ◽  
Author(s):  
Matt K. Broadhurst ◽  
Russell B. Millar
Keyword(s):  
Mesh Size ◽  
Optimal Configuration ◽  
Marine Science ◽  
Future Studies ◽  
Size Classes ◽  
Scale Assessment ◽  
Posterior Section ◽  
Wide Scale ◽  
Simultaneous Comparisons ◽  
Commercial Size

Abstract Broadhurst, M. K., and Millar, R. B. 2009. Square-mesh codend circumference and selectivity. – ICES Journal of Marine Science, 66: 566–572. Despite the wide-scale assessment and the use of square-mesh codends in demersal trawls, relatively few studies have tested the effects of configurations other than mesh size on their selectivity. We investigated the consequences of increasing the circumference of square-mesh codends used in an Australian penaeid fishery from the expected optimal configuration of ∼33% of maximum diamond-mesh extension to ∼56 and 75%. Three square-mesh designs comprised 27-mm polyamide mesh throughout and had the same length (100 bars, B), but different circumferences (90, 150, and 200 B, respectively). Paired simultaneous comparisons (using twin trawls) of each treatment codend against a small-meshed control revealed significant effects of circumference on the efficiency of the trawl for a small teleost (pink-breasted siphonfish, Siphamia roseigaster) and commercial size classes of school prawns (Metapenaeus macleayi). Compared with the 90 codend, pink-breasted siphonfish catches and prawn count (numbers per 500 g) were both significantly greater in the codends of larger circumference, and these effects are attributed to concomitant (i) convoluted or reduced lateral openings of meshes and (ii) lesser probabilities of organisms encountering meshes in the posterior section. These differences would not preclude the use of codends of larger circumference in the fishery, but they do highlight the need to select appropriate configurations in future studies to reduce the potential for including the confounding effects of different geometries.

Modelling pulse fishery systems in data-limited situations

2020 ◽  
Author(s):  
Arnaud Grüss ◽  
Derek G Bolser ◽  
Brad E Erisman
Keyword(s):  
Marine Fish ◽  
Mortality Rates ◽  
Marine Science ◽  
Spawning Aggregation ◽  
Fishing Mortality ◽  
Strong Basis ◽  
Timing Of Reproduction ◽  
Trade Off ◽  
Future Studies ◽  
Fisheries Science

Abstract Per-recruit models have been widely used since the onset of modern fisheries science, particularly in data-limited situations. When the study fishery is a pulse fishery, namely a fishery operating over a brief period followed by a long fallow period, exploitation rates rather than fishing mortality rates are employed to calculate per-recruit quantities. The literature suggests that a discrete per-recruit model is more appropriate than a continuous per-recruit model when per-recruit quantities are expressed as a function of exploitation rates. For this reason, Erisman et al. [Erisman, B. E., Grüss, A., Mascarenas-Osorio, I., Lícon-González, H., Johnson, A. F., and López-Sagástegui, C. 2020. Balancing conservation and utilization in spawning aggregation fisheries: a trade-off analysis of an overexploited marine fish. ICES Journal of Marine Science, 77: 148–161.] recently developed a discrete per-recruit model to examine the impacts of altering exploitation rates for the Gulf corvina (Cynoscion othonopterus) pulse fishery. Using Erisman et al.’s (Erisman, B. E., Grüss, A., Mascarenas-Osorio, I., Lícon-González, H., Johnson, A. F., and López-Sagástegui, C. 2020. Balancing conservation and utilization in spawning aggregation fisheries: a trade-off analysis of an overexploited marine fish. ICES Journal of Marine Science, 77: 148–161.) data, we demonstrate in detail that, under certain conditions, it is reasonable to employ a continuous per-recruit model for a pulse fishery system. We then use the designed continuous per-recruit model to demonstrate how the timing of the pulse fishery within the year relative to the timing of reproduction can be accounted for in a per-recruit model, and we explore the impacts of these model developments. This article serves as a strong basis for future studies that model pulse fishery systems in data-limited situations.

scholarly journals Cephalopods in marine predator diet assessments: why identifying upper and lower beaks is important

2011 ◽  
Vol 68 (9) ◽  
pp. 1857-1864 ◽  
Author(s):  
José C. Xavier ◽  
Richard A. Phillips ◽  
Yves Cherel
Keyword(s):  
Marine Science ◽  
Relative Importance ◽  
Future Studies ◽  
Marine Predator ◽  
Predator Diet ◽  
Cephalopod Species ◽  
Diomedea Exulans ◽  
Wandering Albatross ◽  
The World ◽  
Different Parts

AbstractXavier, J. C., Phillips, R. A., and Cherel, Y. 2011. Cephalopods in marine predator diet assessments: why identifying upper and lower beaks is important. – ICES Journal of Marine Science, 68: 1857–1864. Cephalopods are components of the diet of many predators worldwide. They are identified mainly using their chitinized upper and lower beaks, but because it has been assumed that the number of upper and lower beaks would be the same in predator diet samples, more effort has been put into creating keys for the lower beaks, which are more easily identifiable from morphology. A test is made of whether the number of upper and lower beaks differs in diet samples collected from a major cephalopod predator, the wandering albatross (Diomedea exulans), potential biases in the estimation of predator diets are assessed, and upper:lower beak ratios in published studies of other seabirds, seals, whales, and fish from different parts of the world reviewed. The ratio of upper to lower beaks in diet samples from wandering albatrosses varied greatly in a single year (from 69.6% more lower beaks to 59% more upper beaks), and between years (from 0.5 to 32.1% more upper beaks), and biases were greater for certain cephalopod species, resulting in underestimation of their relative importance. Future studies need to consider using both upper and lower beaks to improve the assessment of the contribution of different cephalopods to predator diets.

scholarly journals Correction of the Claim for Microfinance Market of 1.5 Billion Clients

2013 ◽  
Vol 2 ◽  
pp. 18-31 ◽  
Author(s):  
Tomáš Hes ◽  
Anna Poledňáková
Keyword(s):  
Nobel Prize ◽  
Market Potential ◽  
The Real ◽  
Scale Assessment ◽  
Form Part ◽  
Prize Award ◽  
Real Size ◽  
Wide Scale ◽  
Global Estimates

Since the beginnings of modern microfinance in the 70s, the industry continued to grow rapidly, albeit fueled by dubious assumptions related to market potential. Boosted by Nobel Prize award, thousands of new MFIs are currently being created in the lure of market potential, estimated atone and half billion of unattended clients. The estimates, however, differ drastically and there is no wide scale assessment available deducing the unattainable market strata, detrimental to sustainablemicrofinance, from the inflated estimates. The exaggerations are to be denoted as unrealistic andexcluded from the global estimates. This study intends to quantify the market wrongly assumed to form part of the microfinance market and to deduce the real size of the potential global microfinancesector, appraising the size of the market that should not be counted into the integral demand, since it isunsustainable or harmful to the players involved.

scholarly journals Diversity and abundance of epibiota on invasive and native estuarine gastropods depend on substratum and salinity

2015 ◽  
Vol 66 (12) ◽  
pp. 1191 ◽  
Author(s):  
Jakob Thyrring ◽  
Mads Solgaard Thomsen ◽  
Ane Kirstine Brunbjerg ◽  
Thomas Wernberg
Keyword(s):  
Environmental Factors ◽  
Native Species ◽  
Linear Models ◽  
River Estuary ◽  
Generalised Linear Models ◽  
Future Studies ◽  
Shell Type ◽  
Five Factors ◽  
Wide Scale ◽  
Swan River

Our understanding of variation in epibiota communities remains incomplete. This study relates such variability to multiple concurrent environmental factors. Specifically we determined the relative importance of salinity, depth, wave exposure, habitat and ‘shell type’ (shell type combined species, size, morphology and mobility traits) for community structure of sessile epibiota on gastropods in the Swan River Estuary, Australia. We quantified distribution, biofouling patterns, and detailed epibiota community structures on gastropod species in the estuary – the native Nassarius pauperatus and Bedeva paiva and the invasive Batillaria australis. The invasive Batillaria was much more abundant, and more biofouled, than any of the native species, thereby supporting orders of magnitude more epibiota in the estuary. Generalised linear models were used to partition variation in richness and abundance of epibiota among the above listed factors. Of the five factors were only shell type and salinity significant in 9 of 14 models. These results highlight (1) that a single invasive species can alter epibiota communities on a large system-wide scale, (2) an overwhelming importance of shell type and salinity in explaining estuarine epibiota communities, and (3) that additional environmental factors need to be included in future studies to improve predictive models of distribution for epibiota communities.

scholarly journals Ichthyofauna of two reservoirs in the middle Acaraú river basin, Ceará, Northeastern Brazil

Check List ◽  
2013 ◽  
Vol 9 (6) ◽  
pp. 1391 ◽  
Author(s):  
Ronaldo César Gurgel-Lourenço ◽  
Wallace Alves de Sousa ◽  
Jorge Iván Sánchez-Botero ◽  
Danielle Sequeira Garcez
Keyword(s):  
River Basin ◽  
Fish Assemblage ◽  
Fish Fauna ◽  
Mesh Size ◽  
Dry Season ◽  
Northeastern Brazil ◽  
Resources Management ◽  
Future Studies ◽  
Fishing Resources ◽  
Rivers And Reservoirs

Few studies have been published on the taxonomy, biology and ecology of the fish fauna of the rivers and reservoirs from the Brazilian Caatinga. Considering the importance of fish surveys as subsidies for future studies and fishing resources management, the purpose of the present study was to assess the fish assemblage of the two largest reservoirs in the middle Acaraú river basin, the Paulo Sarasate and the Edson Queiroz reservoirs, state of Ceará, Northeastern Brazil. Eight nycthemeral samplings were performed with gillnets (mesh size ranging from 3 to 12 cm between opposite knots) during rainy and dry season between 2010 and 2012. We captured 1,626 specimens belonging to three orders, nine families and 17 species, six of which are endemic to the Caatinga. Approximately 30% of the species observed were non-native and had been introduced for stocking purposes.

scholarly journals From Performance-Based To Inquiry-Based Accountability

2007 ◽  
Vol 16 (1) ◽  
Author(s):  
Sonia Ben Jaafar
Keyword(s):  
Empirical Research ◽  
Current Literature ◽  
Large Scale ◽  
Future Studies ◽  
Large Scale Assessment ◽  
Scale Assessment ◽  
Unique Approach

This paper argues Canada has a unique approach to large-scale assessment and accountability that is not reflected in the current literature. I explore its construction by drawing on the results of two pan-Canadian SSHRC-funded studies and reflecting on Canada’s philosophical identity that distinguishes it from other nations. I conclude with a call for more Canadian-based theoretical and empirical research to support contextually relevant interpretations in future studies.

A trouser-trawl experiment to assess codends that exclude juvenile mulloway (Argyrosomus hololepidotus) in the Hawkesbury River prawn-trawl fishery

1995 ◽  
Vol 46 (6) ◽  
pp. 953 ◽  
Author(s):  
MK Broadhurst ◽  
SJ Kennelly
Keyword(s):  
Anterior Section ◽  
Trawl Fishery ◽  
Posterior Section ◽  
Simultaneous Comparisons ◽  
By Catch

A trouser trawl was used to assess two codends designed to reduce the by-catch of juvenile mulloway in the Hawkesbury River prawn-trawl fishery. Simultaneous comparisons were made between the catches and by-catches from each codend with those from a conventional codend. The new design incorporated a panel of netting (40-mm mesh or 85-mm mesh) sewn such that the meshes were square-shaped. The panel was placed into the top of the anterior section of the codend to allow water and swimming fish to escape through these larger openings while allowing prawns to tumble along the conventional diamond-shaped netting (40-mm mesh) on the bottom of the codend (and be retained in the posterior section). Comparisons with a conventional codend (in which all meshes were diamond-shaped) showed that the codend with the 40-mm square-mesh panel reduced the by-catch of small mulloway by a mean of 44% without significantly reducing the catch of prawns. The 85-mm square-mesh panel was excluded from analysis, owing to problems associated with its construction.

Size Structure of the Plankton Community Along the Trophic Gradient of Lake Memphremagog

1983 ◽  
Vol 40 (10) ◽  
pp. 1770-1778 ◽  
Author(s):  
Robert Henry Peters
Keyword(s):  
Trophic State ◽  
Size Structure ◽  
Geometric Mean ◽  
Mesh Size ◽  
Particulate Phosphorus ◽  
Phosphorus Concentration ◽  
Community Size ◽  
Millipore Filter ◽  
Size Classes ◽  
Filter Size

The size distribution of epilimnetic plankton at four sites of differing trophic state was examined from May 1977 to May 1978 to examine the applicability to lakes of Sheldon's hypothesis that logarithmically ordered size classes contain approximately constant concentrations of biomass. The plankton was sized by serial filtration through a series of screens of mesh size 102, 75, 55, 35, 20, and 10 μm and a 0.45-μm Millipore filter. Biomass in each fraction was measured as particulate phosphorus concentration. I tested the hypothesis by examining the fit of regressions of particulate P concentration in each sequential fraction against the logarithm of the geometric mean of the meshes used to delimit that fraction. Sheldon's hypothesis leads one to expect a linear relationship. In most cases this was found but exceptions were common, and some size classes contained significantly more or less P than the linear model (Sheldon's hypothesis) would suggest. Comparison of the amount of P in the size classes I studied with previous estimates of the biomass of zooplankton and fish suggest that larger organisms may also fit the relation. The slope and intercept of these regressions between biomass and filter size increase with lake trophic state. This may allow an approximate prediction of community size structure in other lakes based on measured or predicted concentrations of total phosphorus.

Screen Mesh Size Affects Estimates of Macro- and Meio-benthos Abundance and Biomass in the Great Lakes

1981 ◽  
Vol 38 (9) ◽  
pp. 1027-1034 ◽  
Author(s):  
Thomas F. Nalepa ◽  
Andrew Robertson
Keyword(s):  
Great Lakes ◽  
Body Length ◽  
Water Depth ◽  
Lake Michigan ◽  
Mesh Size ◽  
Dry Weight ◽  
Head Capsule ◽  
Future Studies ◽  
Almost All ◽  
Screen Mesh

The efficiencies of screens with mesh openings of 595 and 106 μm in retaining, respectively, the macro- and meio-benthos were measured for samples taken in southeastern Lake Michigan. The use of these screens provides adequate estimates of dry weight biomass for both the macro- and meio-benthos, but serious underestimates of the numbers of many taxa, most notably naidids, enchytraeids, chironomids, nematodes, and rotifers, can result. For chironomids, retention on the 595-μm screen varied by species, with overall retention being closely related to both body length and head capsule width. Retention for certain macro-benthic taxa was significantly related to sampling date and water depth, indicating that future studies concerned with these variables should use mesh sizes small enough to retain all (or almost all) of the individuals of the taxa of interest.Key words: mesh size, screen efficiency, percent retention, macrobenthos, meibenthos, Lake Michigan

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