Discards in North Sea fisheries: causes,consequences and solutions

Discards refer to that part of the catch returned to the sea during fishing operations. This study assesses the consequences, causes, and potential solutions to the discard problem using the example of North Sea fisheries. Fishermen's immediate objectives during fishing operations and the low confidence in projected gains from discard reduction measures have promoted use of unselective trawls while the poor enforcement of the quota system has exacerbated discard quantities. It is concluded that a reduction in discard rates is required for a long-term solution to the ecological and economic costs of discarding and the development of fishing opportunity incentives can promote the use of more selective fishing techniques.     

Estimating global discards and their potential reduction for the Galician fishing fleet (NW Spain)

This study presents the first comprehensive estimation of discard amounts in the Galician fishing fleet, in order to provide an integral view of this increasing environmental problem at a regional scale. Subsequently, a series of improvement actions relating to discard minimization are suggested with the goal of enhancing the performance of the Galician fishing fleet through discard minimization. Discard estimates were constructed individually for the different Galician fisheries by aggregating primary data obtained from a total of 89 fishing vessels and secondary data for those fleets that were not directly sampled. Results showed that roughly 60,250 t of marine organisms were discarded by the Galician fleet in 2008, representing 16.9% of the total capture. Moreover, an important percentage of these discards were linked mainly to trawling vessels and to a lesser extent, to certain long lining fisheries. Therefore, improved management measures in target stocks should take into account the fact that alternative fishing gears other than trawl nets may reduce the amount of discards for certain species. This estimation may improve the assessment of stocks and help to quantify the damage that discards may have on wild ecosystems.     

To land or not to land: How do stakeholders perceive the zero discard policy in European small-scale fisheries?

The landing obligation recently adopted by the European Union's (EU) Common Fisheries Policy aims to eradicate discards in EU fisheries. The objective of this paper is to investigate the potential social and economic impacts of the discard ban in European small-scale fisheries (SSF) and the critical factors for its successful implementation. An exhaustive systematic literature review and a stakeholder consultation were carried out in order to (i) collect detailed information about current knowledge on discards in EU SSF and gauge stakeholder perceptions about potential impacts of the discard ban in European SSF, (ii) examine the capacity of the SSF industry to implement the discard ban, and (iii) explore the limits and feasibility of implementing such a measure.The results of this study show that little attention has been given by the scientific community to discards in EU SSF. Indeed, the systematic literature review shows that this problem is relatively unexplored in the EU. In addition, the effectiveness of a discard ban in industrial fisheries is still unclear, mainly because discard data are not systematically collected by fisheries authorities. Stakeholders mostly perceive that the new landing obligation was developed with industrial fisheries in mind and that compliance with the landing obligation in EU SSF will be difficult to achieve without high economic costs, such as those related to the handling and storage of unwanted fish on board.     

Resolving the discard problem—A case study of the English Nephrops fishery

The phenomenon of discarding was studied using a multidisciplinary approach to allow the integration of biological, social and economic data. The research aimed to evaluate the strength of the case to reduce discarding in a single case study fishery, the English Nephrops fishery; to identify specific objectives for discard reduction; to identify factors that inhibit discard reduction and to determine the best means of achieving those objectives. Changes in trawl structure offered the best solution while having the least impact on fishing opportunities. However, the inadequate level of incentive was identified as the main impediment to discard reduction rather than the lack of technical ability. To implement effective measures to reduce discarding in this fishery, an increased level of incentive is required. Three measures are identified as a means to achieve this.     

副渔获物对渔业资源的影响及其减少方法的探讨

由于渔具不同的选择性和多鱼种鱼类共栖 ,人们在对目标种类进行捕捞时 ,不可避免地产生副渔获物及其抛弃。由于渔业资源的下降和人们对海洋环境保护意识的加强 ,副渔获物及其抛弃问题日益成为人们关注的焦点。本文对世界范围内的渔业活动所产生的副渔获物进行分析 ,根据副渔获物的种类、被抛弃情况和原因以及对渔业资源的影响 ,提出了减少副渔获物和抛弃的方法。     

The discard ban policy,economic trends and opportunities for the Portuguese fisheries sector

In this paper the discard ban policy within the Portuguese fisheries sector is discussed and the opportunities and impact in the fisheries economy that arise from sales of unwanted fish under the new landing obligation are evaluated. The decadal mean price of fish (€/kg, adjusted for inflation) rose from the 1940s until the 1970s, dropping thereafter. The yearly averaged economic income estimated for discards sales between 1969 and 2009 ranged from 419345€ to 2164379€. Discard ban sales could contribute from 10% to 53% of the total landed value and 9–34% of the total catches (landings + discards). Under a discard ban policy, the fishing sector with the largest economic contribution for total discards sales would be multispecies (54%), followed by trawl (26%) and seine (20%). On average, fishing sales contributed with 0.63% to gross domestic production (GDP) between 1938 and 2009. Discard sales can increase 1.07–1.46 times more than the fish landing contribution to GDP. After 1983 the average landings/imports economic ratio was 0.28:1, which means that fish imports surpassed landings economic value 3.57 fold. The discard ban policy can create economic opportunities in the national context thus helping to revitalize some specific fisheries sectors.     

Numerical experiments on estimating the accuracy of the methods of solution of the Kalman smoothing problems

The model numerical experiments on estimating the accuracy of two methods for solving the problem of Kalman smoothing, both iteration and precise, are described on the basis of a simple equation for the passive admixture transport. Some quantitative estimations are given.Translated by Mikhail M. Trufanov.     

Discard management: A spatial multi-criteria approach

Discard management needs to draw on scientific research and advice, usually supported by specific statistical modeling analysis. A wide range of statistical analysis methods were applied to fishery data in an attempt to distinguish factors that influence the species discard composition. While such approaches are important, they are still incomplete for disaggregating the economic and spatial-temporal factors for analyzing of this process and obtain a whole view of this issue. Our study aims to fill this gap by identifying, describing, and quantifying factors that influence discards of trawl fisheries using a multivariate approach based on five complementary aspects: “economic”, “vessel characteristics”, “spatial”, “temporal” and “environmental”. In addition, a spatial multi-criteria approach were used to investigate discard hot-spot areas using ecological criteria such as vulnerability and resilience of the discarded species. Using these ecological criteria will concentrate conservation efforts on the most relevant sites minimizing discards of a variety of potentially vulnerable species. This approach was applied to a case study of a multi-species demersal bottom trawl fisheries in north Spain, Cantabrian Sea (ICES area VIIIc). Results showed how spatial and economic factors highly affect species discard composition, identifying specific spatial-temporal discard hot-spots to be preferentially avoided by fishers. Mitigation measures for future fisheries management strategies should be implemented at multiple stages of the discarding process, both in the selection of the fishing grounds and the economic valorization of the discarded species.     

Unreported bycatch in the New Zealand West Coast South Island hoki fishery

There are recognised benefits to managing fisheries by individual transferable quotas (ITQs), but ITQs may increase incentives to discard fish.     

Simulation of the internal tide in the Strait of Bab el Mandeb (the Red Sea)

The baroclinic tide in the Strait of Bab el Mandeb is simulated by solving a three-dimensional boundary-value problem in boundary-fitted coordinates for the equations of dynamics, density constituents, and turbulence characteristics. Results related to simulations of the barotropic tide in the Red Sea and to the internal tide in the Strait of Bab el Mandeb are presented.     

The dynamical and thermodynamical analysis of the oceanic response to storm

In this paper, the discussion is made on the problem of the oceanic response caused by air-sea interaction under storm. First, the perturbation differential equations for the problem are given, and the interaction functions are supposed to be the solving conditions. Next, the nonlinear diffusion equations of the problem are solved by using the method of the given variable transforms and the specific variable power series. Finally, the response disturbances to the circular intense storm is calculated so as to discribe quantitatively the evolution processes of the oceanic response.     

Application of data on seawater light scattering for the study of marine particles: a selective review focusing on Russian literature

This paper presents a selective review of applications of data on seawater light scattering for the study and monitoring of marine particles. Particular emphasis is placed on ocean waters and the seas surrounding Russia, where earlier studies by the author with his coworkers are little known because published mostly in Russian. In those assessments, methods of solving the inverse problem of seawater light scattering have been developed. Low-parametric models of optical properties were created by means of statistical analyses of experimental data, solving the inverse problem and comparing results derived from optical methods with those based on particle counts. Estimates of the volume and mass concentrations of suspended matter and its components were derived from light-scattering data for different regions. The potential of using optical methods for assessing spatiotemporal variability in suspended matter supply, propagation, and distribution is also considered.     

The prediction of the dynamic and structural motions of a floating-pier system in waves

In this study, a two-dimensional floating pier consists of single rectangular impermeable pontoon with side supporting pile-columns is studied. The purpose of this study is to present a theoretical solution for the linearized problem of incident waves exerting on a floating pier with pile-restrained. All boundary conditions are linearized in the problem, which is incorporated into a scattering problem and radiation problem with unit displacement. The method of separation of variables is used to solve for velocity potentials. For the radiation problem with unit heave and pitch amplitude, the boundary value problem with non-homogeneous boundary condition beneath the structure is solved by using a solution scheme. By calculating the wave force from velocity potential and solving the equation of motion of the floating structure simultaneously a close form theoretical solution for the problem is developed. The finite element method was also applied to calculate the dynamic responses on the supporting piles subjected to the pontoon motions and incident waves.     

Variational Method for Solving the Quasi-Geostrophic Circulation Problem in a Two-Layer Ocean

Izvestiya, Atmospheric and Oceanic Physics - A new variational formulation and a method for solving the problem of quasi-geostrophic dynamics in a two-layer periodic channel are considered. The...     

海底边坡稳定性分析中波浪力的求解

针对浅水区波浪的非线性特性,提出了在海底边坡稳定性分析中应用椭圆余弦波理论来研究波浪力的问题,利用非线性弥散关系建立了新的适用于整个水深范围的椭圆余弦波的近似求解方法.结合工程实例,确立了海底边坡波浪力的计算步骤,并编制了计算程序.     

Variational Approach to the Problems of Planning of Experiments and Identification of the Input Parameters of Hydrodynamic Models According to the Data of Measurements

We discuss the computational properties of variational algorithms of mastering the data of measurements and convergency of iterative procedures of search for an optimum distribution of the input parameters of a model and consider the model of transfer of a passive admixture. The algorithm of identification is based on the variational principles, solving the conjugate problem, and minimization of the functional of quality of a prediction. We carry out the analytic verification of the efficiency of the algorithm and discuss the problems of optimum planning of experiments from the viewpoint of conditionality of the problem of identification that is being solved.     

Identification of the initial oceanographic field by means of the variation algorithm of measurement data assimilation

The variation algorithm of data assimilation is considered which is based on the minimization of some quadratic functional of the prediction quality and the solution of a conjugated problem. Numerical experiments of the model have been carried out which demonstrate the potentialities of this approach and the prospects of its employment for solving practical problems.Translated by Mikhail M. Trufanov.     

沿海砼结构耐久性问题研究现状与对策

混凝土耐久性能不良引起的适用性、安全性问题以及由此引发的环境、能源、经济问题在全球范围内已引起广泛的关注.而沿海城市经济的飞速发展和大规模的开发海洋资源使得混凝土结构面临严峻的海洋环境的挑战.因此,了解沿海混凝土结构耐久性问题的研究现状与对策具有十分重要的现实意义.综合分析了沿海砼结构性能退化的原因及解决办法并在此基础上指出进一步研究的可能方向.     

Dynamics of the two-dimensional ideal incompressible fluid and Casimirs

Problems are considered in which the role of Casimirs in forming dynamics of the two-dimensional ideal incompressible fluid is basically studied; in particular, the conditions are formulated which arise in the stability problem of two-dimensional flows in the presence of Casimirs. Some general approaches to the construction of difference schemes for solving equations of two-dimensional fluid which possess the given Casimirs are considered.