1,721,023 research outputs found
Workshop on ICES reference points (WKREF2)
No full textThe ICES Workshop on ICES reference points (WKREF2) was tasked review the WKREF1 report and based on the outcome develop updated guidelines for the ICES reference points system and recommendations for ACOM consideration. The WKREF1 report has suggested 5 key recommendations to simplify and harmonise the ICES reference points framework representing a major change to the current guidelines. At WKREF2, we detailed discussions and four key concerns were raised about the proposed approach. The first related to the simplification of rules to define Blim. Around two thirds of category 1 stocks would end up as WKREF1 “Blim Type 2” where Blim would be set as a fraction of B0. The Allee effect or “depensation” maybe more important than previously thought and should be furthered explored for ICES stocks since it has important consequences for Blim. A number of challenges and issues around defining Blim using the current guidelines were documented. Some suggestions on improvement criteria were discussed including using classifiers to define spasmodic stocks and using change point algorithms to address non-stationary productivity regimes. However, further work is need to make these approaches operational and there was no consensus that the WKREF1 Blim types should replace the current guidelines.WKREF1 recommended that the FMSY proxy should be based on a biological proxies and should be less than the deterministic FMSY. It was pointed out that the stochastic FMSY estimated in EqSim for example, is lower than the deterministic FMSY and that the current guidelines ensure that the FMSY should not pose a more than 5% risk to Blim. A large amount of work described in WD 1 was carried out to develop an MSE framework to consistency and robustness test a candidate reference point system for North East Atlantic stocks. However, WKREF2 recommended that further work needs to be carried out to condition and test the simulation framework before the conclusions could be adopted by ICES and incorporated into the guidelines.A number of considerations for defining MSY related reference points were discussed including using model validation and prediction skill to ensure that ICES provide robust and credible ad-vice. There is evidence that density dependence (DD) is important in the majority of ICES stocks (68% in recruitment and 54% in growth). The correct prediction of the shape and strength of density-dependence in productivity is key to predicting future stock development and providing the best possible long-term fisheries management advice. A suggested approach to use surplus production models (SPMs) to account for DD in FMSY was suggested and discussed but there was no consensus on whether that approach was appropriate. There was consensus that the FECO approach as a means of adapting target fishing mortality to medium-term changes in productivity should be included in the guidelines subject to a benchmark and ACOM approval.While WKREF1 and 2 focused mainly on Category 1 stocks ToR c) called for a “simplified and harmonised set of guidelines for estimating MSY and precautionary reference points applicable in the advice framework across various ICES stock categories.” Ideally the ICES assessment categories should provide equivalent risk across all stocks. This issue was discussed but no recommendations emerged.There was no consensus a revised reference point framework was proposed at WKREF2. However, it was agreed that it should be presented here for further discussion at ACOM and other fora. The key feature of the suggested approach is that the stock status evaluation is treated independent of the Advice Rule (AR). The main feature of the system is that the biomass trigger is not linked to a stock status evaluation, it is linked to the expected biomass when fishing at the target fishing mortality, in contrast to the current ICES approach. It also entailed that FMSY would also become an upper limit of fishing mortality and that the advised fishing mortality would be set at or lower than that level. WKREF2 did not discuss what to do in situations where SSB< Blim or alternative forms of HCR for the advice rule. Building community understanding and consensus around simplified and harmonised guidelines has yet to be achieved. A further workshop WKREF3 will be required to achieve that aim. The report includes 6 recommendations for ACOM consideration
The drivers and dynamics of fisher behaviour In Irish fisheries
Full text linkIt is widely acknowledged within the scientific community that a single species approach to European mixed fisheries can result in species-specific advice inconsistent with multi-species management objectives. Within the reformed Common Fisheries Policy a move toward mixed fisheries and ecosystem based management is encouraged. The overall objective of this research was to improve understanding of the complex targeting behaviour undertaken by commercial fishers. Whereby, improved understanding will enhance the ability to predict the responses to future mixed fisheries management measures and changing economic conditions within the Irish fishing industry. Irish métiers (groups of homogeneous fishing trips) highlight the complexity of fishing activities within the Irish fleet, having identified 33 otter trawl métiers and 19 in the remainder of the fleet. Métier dynamics identified over compensation to introduced management, resulting in effort displacement and increased temporal specific fishing pressure. Therefore were deemed as appropriate base units for all subsequent analyses. Two economic variables, operational fishing cost and trip landings value, considered to represent important drivers were developed. This lead to application of a general additive model to estimate and predict fuel consumption estimates according to fleet segment definitions. A linear mixed effects model with random vessel effect was developed as a method of standardising value generating an index of value per unit effort. This identified kilowatt fishing days as the most appropriate effort measure. The final investigation stage successfully amalgamated the knowledge gained into the formulation of novel Markov transition probability for a multinomial model to predict fisher métier strategy choice. This is to be incorporated into management strategy evaluation, aiding the assessment and possible impacts of future management proposals on the Irish fleet and commercial stocks around Ireland. Developments presented will benefit the progression toward optimising sustainability within a mixed fisheries approach to management through incorporation of economic considerations
The drivers and dynamics of fisher behaviour In Irish fisheries
Full text linkIt is widely acknowledged within the scientific community that a single species approach to European mixed fisheries can result in species-specific advice inconsistent with multi-species management objectives. Within the reformed Common Fisheries Policy a move toward mixed fisheries and ecosystem based management is encouraged. The overall objective of this research was to improve understanding of the complex targeting behaviour undertaken by commercial fishers. Whereby, improved understanding will enhance the ability to predict the responses to future mixed fisheries management measures and changing economic conditions within the Irish fishing industry. Irish métiers (groups of homogeneous fishing trips) highlight the complexity of fishing activities within the Irish fleet, having identified 33 otter trawl métiers and 19 in the remainder of the fleet. Métier dynamics identified over compensation to introduced management, resulting in effort displacement and increased temporal specific fishing pressure. Therefore were deemed as appropriate base units for all subsequent analyses. Two economic variables, operational fishing cost and trip landings value, considered to represent important drivers were developed. This lead to application of a general additive model to estimate and predict fuel consumption estimates according to fleet segment definitions. A linear mixed effects model with random vessel effect was developed as a method of standardising value generating an index of value per unit effort. This identified kilowatt fishing days as the most appropriate effort measure. The final investigation stage successfully amalgamated the knowledge gained into the formulation of novel Markov transition probability for a multinomial model to predict fisher métier strategy choice. This is to be incorporated into management strategy evaluation, aiding the assessment and possible impacts of future management proposals on the Irish fleet and commercial stocks around Ireland. Developments presented will benefit the progression toward optimising sustainability within a mixed fisheries approach to management through incorporation of economic considerations
Estimating fish stock population parameters from bottom trawl surveys: sources and magnitude of uncertainty
Full text linkFisheries surveys are widely used in the stock assessment process by providing time series of relative abundance and recruitment strength. Surveys also provide biological data that have the potential to improve stock projections by providing alternatives to the use of spawning stock biomass as a measure of stock reproductive potential. The objective of the present work is to illustrate various sources of error in survey data,
using examples from bottom trawl surveys and to provide innovative methods for identifying and minimising these errors. In Chapter 1, the current work is framed
within the existing literature and an overview is given of the different sources of error. The next six chapters consist of papers that have been published, are in press, or under review with peer-reviewed journals. These papers consist of case-studies, each exploring a different source of error. In Chapter 2, a method for summarising the precision of a length-frequency distribution is presented and recommendations are
given on the sample sizes required to achieve a particlar precision level. In Chapter 3, the variability in the assignment of maturity stages of plaice (Pleuronectes platessa, L.) and whiting (Merlangius merlangus, L.) is examined, using statistical techniques developed in the social sciences. In Chapter 4, the spatial variability in the age-length structure of haddock (Melanogrammus aeglefinus, L.) is explored and a new method for comparing age-length keys is developed. In Chapter 5, the spatial structure in the length-weight relationships of whiting and haddock are analysed using geostatistical
tools. In Chapter 6, the spatial trend in the sex ratio of megrim (Lepidorhombus whiffiagonis, Walbaum) is explored using generalized additive modelling techniques.
In Chapter 7, spatial trends in the proportion of mature cod (Gadus morhua, L.) are investigated. In the concluding Chapter 8, the scale of various errors is reviewed in the light of the current work and recommendations for sampling design are proposed
Larval transport dynamics in Nephrops norvegicus
No full textTransport of meroplankton larvae in the ocean is a crucial process as it enables connectivity between populations and determines larval supply for species with narrow habitat requirements and sedentary adult stages. The Norway lobster (Nephrops norvegicus), Europe’s most important commercial crustacean, has a patchy distribution across the Northeast Atlantic Ocean and Mediterranean Sea. Adults inhabit areas of muddy substrate where they excavate and spend most of their time within burrows. The pelagic larval phase enables connectivity between populations separated by uninhabitable substrate. Larvae rely on settlement on suitable mud habitat for survival. Therefore, larval settlement, driven by local hydrography, may act as a constraint on recruitment. Biophysical models offer a method of simulating larval transport, which is extremely difficult to observe in-situ due to the inherent difficulties in tracking miniscule larvae in vast areas of the ocean. In the current study, a biophysical larval transport model was used to estimate larval retention, dispersal distance and connectivity for N. norvegicus grounds around Ireland. Models parameters were supported by empirical data in order to accurately represent the biological and behavioural processes of larvae.
In Chapter 2, the vertical distribution and occurrence of a Diel Vertical Migration (DVM) in N. norvegicus larvae was examined. Larval vertical distribution was influenced by the vertical temperature differential in the water column, zooplankton biomass and the potential energy anomaly. A twilight DVM was identified and involved two ascents and two descents per day. In Chapter 3, historical zooplankton datasets were used to identify an earlier larval phenology shift in N. norvegicus by 19.1 days from 1982 - 1995 to 2000 - 2010. Ocean warming was identified as the most likely cause as increasing temperatures led to a contraction of the embryo incubation period and earlier hatching of larvae. The phenology shift appeared to have a limited effect on larval duration and transport. Only large variations in modelled larval retention and dispersal distance were observed between larvae released very early and very late in the season. In Chapter 4, a 20-year time series of modelled larval retention, dispersal distance and connectivity estimates for 6 N. norvegicus Functional Units (FUs) demonstrated their capacity to retain, import and export larvae. Smaller FUs had a decreasing trend in retention over the time series which appeared to be as a result of strengthening currents. On the Aran grounds, a link between modelled larval retention and dispersal distance and empirically observed burrow densities from underwater television with a 3-year lag was observed.
The findings indicate that larval transport may act as a constraint on recruitment for N. norvegicus populations like the Aran grounds with low and variable larval retention and limited larval imports due to spatial isolation from other grounds. It demonstrates the potential of using larval transport estimates to identify instances of poor recruitment, due to low larval settlement, early in the life cycle before its effects manifest in the adult population. It can also be applied to similar species with defined habitat and planktonic life stages and may assist in limiting overexploitation for commercial species, particularly in the face of climate change and the likely impacts on oceanography.2022-02-0
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Modelling the ecology, dynamics and assessment of Nephrops norvegicus (Linnaeus 1758) in the waters around Ireland
Full text linkNephrops norvegicus is a valuable market species in the North-East Atlantic and it is of economic importance to Ireland. The present study investigated the status of the Aran ground stock, frequently ranked within the top two commercially valuable “fish” landed. Since 2002, under water TV surveys have been developed to provide a fishery independent estimate of burrow abundance in areas that exhibited a steady decrease in Nephrops over two decades contrasting with the increasing landings. In order to identify stock status and provide reliable information to management, we used a number of different approaches in the fields of time series analysis, spatial analysis and fisheries stock assessment.
We examined the temporal fluctuations in a 16 year time series of landings in Aran grounds and found fluctuating cycles within an overall decreasing trend. This stock dynamic was also compared with the other main areas of harvest off the coast of Ireland (Smalls ground, Porcupine Bank, and the west Irish Sea) disclosing a regional common trend in the pattern of the stocks for connecting areas.
Regional climatic influences (e.g NAO, AO and AMO) have been detected on various time scales ranging from month to years and the time series analysis method appears effective for detecting changes in fishing behaviours.
Spatial analysis of the burrow density over the stock area revealed patchy distribution varying in size and intensity over the years with a spatio-temporal trend marked by a depletion of abundance in midfield with noticeable consequences for fishing vessel activity at a regional level. This spatial approach enabled the evaluation of the influence of the mud content of the seabed on the density of burrows and to explore the potential impact of the prevailing current circulation pattern during the planktonic stage of Nephrops on the level of recruitment by using remote sensing data.
For an optimal fisheries management strategy, demographic information for the exploited species is necessary and for Nephrops, effective stock assessment is hampered because of the difficulty in age determination. A biomass model with a Schaefer surplus yield component and a data limited CMSY method were chosen to address the lack of age data and to predict biomass and related key fisheries reference points. Both approaches underline the ongoing decline of Nephrops abundance and reveal warning signals of unsustainable fishing exploitation
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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