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Discards represent one of the most important issues within current commercial fishing. It occurs for a range of reasons and is influenced by an even more complex array of factors. We address this issue by examining the data collected within the Danish discard observer program and describe the factors that influence discarding within the Danish Kattegat demersal fleet over the period 1997 to 2008. Generalised additive models were used to assess how discards of the 3 main target species, Norway lobster, cod and plaice, and their subcomponents (under and over minimum landings size) are influenced by important factors and their potential relevance to management. Our results show that discards are influenced by a range of different factors that are different for each species and portion of discards. We argue that knowledge about the factors influential to discarding and their use in relation to potential mitigation measures are essential for future fisheries management strategies.

Results from life cycle assessment (LCA) studies are sensitive to modeling choices and data used in building the underlying model. This is also relevant for the case of fisheries and LCAs of fish products. Fisheries' product systems show both multifunctionality because of the simultaneous co‐catch of multiple species and potential constraints to supply due to natural stock limits or socially established limits such as quota systems. The performance of fisheries also varies across seasons, locations, vessels, and target species. In this study, we investigate the combined effect of modeling choices and variability on the uncertainty of LCA results of fish products. We use time series data from official Danish statistics for catch and fuel use of several fisheries disaggregated using a top‐down procedure. We apply multiple modeling approaches with different assumptions regarding the type of partitioning, substitution, and constraints. The analysis demonstrates that, in the presence of relevant multifunctionality, the results are substantially affected by the modeling approach chosen. These findings are robust across years and fisheries, indicating that modeling choices contribute to uncertainty more than the variability in fishing conditions. We stress the need for a more careful alignment of research questions and methods for LCA studies of fisheries and recommend a very transparent statement of assumptions, combined with uncertainty and sensitivity analysis. This article met the requirements for a gold‐gold data openness badge described at http://jie.click.badges. [ABSTRACT FROM AUTHOR]

The European Union's landing obligation includes an exemption for species with documented high survival rates. This is highly relevant for the cod (Gadus morhua) stock in the Baltic Sea, being in a critical state. This study provides initial information on potential discard survival rates for cod (Gadus morhua) caught in trammel nets in the Baltic Sea. Catch-damage-index (CDI) and Reflex Action Mortality Predictor (RAMP) scores were used to assess fish condition immediately after capture and at the end of observation periods. A total of 61 cod were caught in eight different net fleets fished during three trials. Two cod died in the net and three cod died during the observation period from two to 10 days. The results indicate a potential in dedicating resources to cod discard survival studies. • High short-term survival rate in trammel net caught cod at wintertime in the Baltic Sea. • High vitality in discarded cod. • Indication of potential in conducting comprehensive cod discard survival studies. [ABSTRACT FROM AUTHOR]

Norway lobster Nephrops norvegicus fisheries are often characterized by high bycatch and discard rates. However, fisheries species exhibit differences in vertical behaviour that can be used to develop selective devices. We developed a separator frame that can be inserted into the forward part of a cod-end to divide it into a bottom cod-end and a top cod-end. In the top cod-end we inserted a 3-m-long window constructed of 274-mm mesh. The separator frame was tested from a commercial vessel in the Kattegat and Skagerrak area. Small mesh net bags were used to collect the catch going through the separator frame and ending up in the bottom cod-end, the top cod-end, or penetrating the window. The majority of Norway lobster and flatfish entered the bottom cod-end, and most gadoids entered the top cod-end. A relatively high proportion of gadoids and flatfish that entered the top cod-end penetrated the window. The separation was size dependant for some of the investigated species. [ABSTRACT FROM AUTHOR]

The overall objective of this study was to evaluate the behavior of different codend designs to provide basic information that is relevant for implementing technical management measures, improving selectivity and catch quality, and reducing energy consumption. Six different codend designs were evaluated: a traditional diamond mesh codend; a T90 codend (meshes turned 90°); a Bacoma codend with diamond meshes in the lower panel and square meshes in the upper panel; a Bacoma codend with the square meshes orientated in the T0 direction; a two panel square mesh codend; and a four panel square mesh codend. The codends were tested in a flume tank with flow of 1.8 knots/h. A simulated catch of 500 kg was placed in the tested codend. A motion tracking system was used with four track markers placed on each of three successive cross-sections and a single marker at the end of the codend. This made it possible to assess and compare the movements of the codend and the netting in three dimensions. The drag of the codends also was measured and compared. [ABSTRACT FROM AUTHOR]

A number of solutions, with varying efficiency, have been proposed to mitigate discards. In this paper twelve mitigation measures were reviewed by their strengths and weaknesses, along with opportunities and threats, they might entail. How mitigation methods could either support or counteract others was also reviewed. The analyses of the mitigation measures are based on expert knowledge and experience and supported with existing literature. Discarding is highly variable and is influenced by numerous biological, technical and operational factors as well as social and economic drivers. These influences need to be carefully considered when designing management approaches. Finally, all reforms must be carefully considered within the context of a broader management system. The full management system needs to be thought of coherently to create an incentive framework that motivates fishers to avoid unwanted catches. It is only in this setting that discard mitigation methods may be potentially effective. [ABSTRACT FROM AUTHOR]

To reduce the practice of discarding commercially fished organisms, several measures such as a discard ban and extra allowances on top of landings quotas (“catch quota”) have been proposed by the European Commission. However, for their development and successful implementation, an understanding of discard patterns on a European scale is needed. In this study, we present an inter-national synthesis of discard data collected on board commercial, towed-gear equipped vessels operating under six different national flags spanning from the Baltic to the Mediterranean Seas mainly between 2003 and 2008. We considered discarded species of commercial value such as Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), European hake (Merluccius merluccius), and European plaice (Pleuronectes platessa). Comparisons of discard per unit effort rates expressed as numbers per hour of fishing revealed that in the Mediterranean Sea minimum size-regulated species such as hake are generally discarded in much lower numbers than elsewhere. For most species examined, variability in discard rates across regions was greater than across fisheries, suggesting that a region-by-region approach to discard reduction would be more relevant. The high uncertainty in discard rate estimates suggests that current sampling regimes should be either expanded or complemented by other data sources, if they are to be used for setting catch quotas. [ABSTRACT FROM PUBLISHER]

Simple Summary: Due to the implementation of a landing obligation in fisheries in the European Union (EU), with an exemption for species with "high survival", discard survival studies (henceforth DSSs) have become one of the most politically prioritized fisheries research areas in European fisheries. In contrast to most fisheries science research areas, DSSs are embedded by the EUs animal research welfare directive. This is a challenge, and there has not been any focus on how to implement animal welfare (AW) regulations experimentally in DSSs. This paper focuses on AW regulations in relation to conducting DSSs, but the outreach is much broader. We investigate experimental procedures by bringing in relevant examples, using the output results, and relating this information to relevant AW guidelines and regulations by focusing on implementing 3R principles. Globally, it is estimated that around 10% of the fish that are caught are discarded. This is considered to be a wasteful human marine activity since these fish are often dead or dying. To reduce the high discard rates of commercial fisheries, the European Union (E.U.) has enacted a landing obligation that includes the ability to exempt "species for which scientific evidence demonstrates high survival rates". Therefore, discard survival studies (henceforth DSSs) have become one of the most politically prioritized fisheries research areas in European fisheries. International expert groups have produced guidance reports to promote best practices and to harmonize the methodologies. Nevertheless, there has not been any focus on how to implement animal welfare (AW) regulations experimentally. Discard survival studies are "frontrunners" in fisheries science research areas that are embedded by animal research welfare requirements and are expected to be more restrictive in the future because of an increased public focus on fish welfare. This paper focuses on AW regulations in relation to conducting DSSs, but the outreach is much broader. We investigate experimental procedures by bringing in relevant examples, using output results, and relating this information to relevant AW guidelines and regulations by focusing on implementing 3R principles. [ABSTRACT FROM AUTHOR]

Abstract: Systems that take discrete samples of the catch while trawling are widely used in fisheries investigations. We have developed the Minisampler, a relatively small system to be used particularly on small vessels and small trawls. The device is simple, has low weight and is reasonably cheap to make. The Minisampler consists of a tele-command deck unit, a dunking transducer, a stainless steel frame and one or two acoustical trigger-units. Each of them releases a metal bar that opens/closes a collecting bag. Thus is possible to take two or three remotely controlled discrete samples during a tow. We tested the system successfully in a flume tank and during sea trials from a commercial trawler. The Minisampler is a multi-purpose tool and provides opportunity for new experimental designs to improve scientific work using demersal or pelagic trawls in marine or freshwater environments. [Copyright &y& Elsevier]

Madsen, N., and Valentinsson, D. 2010. Use of selective devices in trawls to support recovery of the Kattegat cod stock: a review of experiments and experience. – ICES Journal of Marine Science, 67: 2042–2050.The spawning-stock biomass of cod (Gadus morhua) in the Kattegat area is at a historically low level. Throughout the past decade considerable efforts have been devoted to research on improving both species and size selectivity of the trawls used in the mixed demersal fishery in the area, because this provides a valuable management tool for reducing the bycatch of cod and reducing mortality, and thus helping to rebuild the depleted stock. Gear research in the area has been focused on devices that allow for continued exploitation of the Norway lobster (Nephrops norvegicus) and flatfish, but minimizing the bycatch. We review the results of previous and continuing experiments with various codend mesh sizes, mesh configurations, escape windows, sorting grids, sorting frames, and separator panels, but also changes in whole-trawl designs. Based on our review, we compare and discuss the gear-related technical measures and their effectiveness in maintaining a commercial fishery on viable stocks, yet protecting cod. We discuss the results in relation to changes in legislation and experience with implementation of new selective devices in recent years. We also discuss ways to create stronger incentives for fishers to participate in gear research and to increase acceptance of more selective gears. [ABSTRACT FROM PUBLISHER]

Abstract: The selectivity of a 99mm trawl codend was assessed using a codend cover fitted with a MultiSampler, which was acoustically triggered to take separate samples at three different phases of the haul. The first sample was collected during towing, the second during haul-up and the third at the surface. A total of 18 hauls were conducted with a commercial fishing vessel west of Scotland. It was demonstrated that escapes take place not only during the tow but also in the short period when the trawl is hauled back from the seabed and when the codend is at the surface. For haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus) and Norway lobster (Nephrops norvegicus), respectively, the mean percentages escaping at the surface were 16, 12 and 38% of the total escape while 17, 8 and 28% escaped during the haul-up phase. Compared to towing, the escape rate (no./min) increased for haddock by a factor 2.7 during haul-up and by a factor 1.7 at the surface, whereas the escape rates of whiting were similar for the three phases. The escape rate of Norway lobster increased by a factor of approximately 7 for both the haul-up and surface phases, compared to the towing phase. The selectivity parameters L50 (50% retention length) and SR (selection range= L75–L25) were estimated and compared for the three different phases and for the whole haul for haddock, whiting and Norway lobster. For all three species there was no significant (P >0.05) difference in L50 between the three phases of the haul. There was also no significant difference for whiting and Norway lobster when comparing the SR of the three phases, whereas the SR was significantly lower for haddock when comparing the surface phase with towing and haul-up. The estimate of L50 when towing was about 6cm lower for haddock and whiting and 9mm for Norway lobster compared to the selection curve estimated conventionally for the whole haul. Finally, the effect of sea state, duration and codend catch on the selectivity parameters were estimated for the individual phases and for the whole haul. A significant effect of at least one variable was found in all phases. [Copyright &y& Elsevier]

Abstract: The objectives were to measure roundfish selectivity and to test if square-mesh windows inserted in the codend could improve the selectivity. Sea trials were conducted with a commercial trawler in the Skagerak area. Three codend types were tested: (1) a standard codend with 104mm meshes; (2) a standard 104mm codend with two 85mm square-mesh side windows; (3) a standard 104mm codend with an 85-mm square-mesh top window. The twin-trawl method was used where one side of the rig had a 35-mm (nominal mesh size) control codend. Hauls of each codend were fitted simultaneously in a fixed- and random-effects model. In total, 24 and 30 hauls of haddock and cod, respectively, were included in the final selectivity analysis. This indicated that insertion of a top window in a standard codend improved the selectivity resulting in a lower selectivity ratio (SR/L50) and a higher L50 for cod and haddock, whereas insertion of side windows gave a lower selectivity ratio for both species, but a higher L50 for cod only. The results suggest that the recent mesh size increase to 120mm in a standard codend is not sufficient to reduce the probability of discards to a negligible level with the existing minimum landing sizes. [Copyright &y& Elsevier]

A rapid decrease of the stock of Baltic cod (Gadus morhua) has provided the incentive to improve the size selectivity in the trawl fishery. Use of escape windows is permitted in the legislation to give means of improving the size selectivity of cod as an alternative to a traditional standard codend. The history of the use of escape windows in the Baltic Sea cod fishery is reviewed. The present escape windows do not function optimally. The objective of this new experiment was to compare an improved design of escape window, which is placed in the upper panel, with that of standard codend. Three standard codends, with 105, 120 and 140 mm nominal mesh size, and three window codends, with 110, 125 and 135 mm window nominal mesh size, were tested during sea trials conducted in June and July from a commercial trawler using a twin trawl rig and the covered codend technique. A fixed and random effects model of the codend selectivity was formulated to analyse the results and determine the effects of codend type, mesh size and other recorded variables. L50 and SR increased significantly with the mesh size. L50 was significantly increased and SR significantly reduced for a window codend with the same window mesh size (WMS) as that of a standard codend. The L50 of the standard codends decreased with catch weight. An unexplained port–starboard effect was found for the window codends where the L50 depended on which of the two trawls the codend was attached to. The potential of these escape windows as a management tool to improve the size selectivity in the Baltic cod fishery is discussed. [Copyright &y& Elsevier]

• Baltic cod stocks are in poor condition. • High discard rates of cod, plaice and flounder are observed in the cod trawl fishery. • New selective codend designs were tested and demonstrated that they can improve size and species selectivity. • The selective codend designs seems to be able to benefit the sustainability of the Baltic trawl fishery. The eastern Baltic cod (Gadus morhua) stock is at a critically low level and recruitment of the western Baltic cod stock is at the lowest observed level in over 30 years. The EU (European Union) landing obligation was introduced in 2015 for cod and in 2017 for plaice (Pleuronectes platessa). Size selective codend designs have been used in the Baltic cod trawl fishery for 25 years; however, there are still relatively high discard rates for cod, plaice and European flounder (Platichthys flesus; henceforth flounder) in the trawl fishery and landings of individuals below the minimum conservation reference size (MCRS). These problems call for additional improvements of species and size selectivity in the cod trawl fishery. In this study, two trawl codend designs were developed and tested to improve species and size selectivity in the Baltic cod trawl fishery. The codends were tested onboard a commercial trawler and the test codends were compared to the conventional Bacoma codend, which was fished simultaneously in a twin trawl rig. New codend designs were based on the Bacoma design, where the first test codend had a bottom net panel made of larger diamond meshes (nominal 130 mm mesh size) to improve selectivity in a cod fishery with high catch rates of flatfish. This codend showed a reduction of plaice and flounder, and cod below 45 cm, in the catches. The other test codend was a full square mesh codend (nominal 120 mm mesh size) developed for a cod directed fishery with low flatfish catches, and showed a marked reduction in the catch of cod below 50 cm, with no differences for flounder and plaice catches. With cod stocks at critically low levels and relatively high discard rates of cod, plaice and flounder, the simple codend designs tested in this study could benefit the sustainability of the Baltic cod trawl fishery, but with some loss of commercially targeted sizes. [ABSTRACT FROM AUTHOR]

Highlights • Simple systems allowed for a detailed description and observation of the fishing process of a Danish anchor seine. • Gear geometry of a Danish anchor seines changes continuously during the fishing process. • Majority of fish enters the seine net within the last quarter of the fishing period. • Fishermen are able to control timing of increasing retrieval speed to prevent losing herded fish. Abstract The Danish anchor seine is an efficient type of active fishing gear used globally. Knowledge of the gear and its operational performance is limited, but needed to ensure efficient fishing and appropriate management. During this study, a combination of GPS loggers, depth loggers, and cameras, were utilized to collect quantitative information about the geometry of the seine net and seine ropes during all stages of the fishing process, and to identify when fish enter the seine net. Measurements of the horizontal and vertical openings of the seine net indicated that gear geometry changed continuously during the fishing process. Underwater recordings from the net revealed that the majority of fish entered the seine net within the last quarter of the fishing period, and that fishermen are able to control the timing of increasing the retrieval speed to prevent losing fish late in the fishing process. Underwater recordings of the seine rope provided qualitative results indicating that interactions with the sea bed are relatively minor in nature. [ABSTRACT FROM AUTHOR]

Abstract: The selectivity for Nephrops (Nephrops norvegicus) in trawl codends generally is poor and the lack of steepness of the selection curve results in high discard rates and/or loss of legal-sized catch. This poor codend selectivity often is attributed to the irregular shape of Nephrops, which to some extent characterizes the problem as insoluble. In the present study, the FISHSELECT methodology was used to examine the selection process of the species in order to identify ways to improve selectivity. The use of three different modes of orientation for contact (contact modes) with the codend meshes explained most of the characteristics of the selection curves for Nephrops obtained experimentally. The contact mode with the smallest cross-section was optimal for mesh penetration and, when evaluated against experimental data, 87.5% of all Nephrops encountering the gear were estimated to meet the netting in this contact mode. The range of configurations of the meshes (e.g., opening angles in the diamond mesh netting) was determinative for the selectivity, and the selective process for Nephrops was found to take place along the entire length of the codend. Simulating selectivity in a diamond mesh codend in which the closed meshes in the forward part of the codend were replaced by more open meshes revealed that the selectivity for Nephrops can be efficiently improved. [Copyright &y& Elsevier]

European plaice (Pleuronectes platessa) is a key species in commercial fisheries in the North Sea, Skagerrak, Kattegat, and Baltic Sea. The reformed European Union Common Fisheries Policy includes the possibility of exemptions from the landing obligation for "species for which scientific evidence demonstrates high survival rates". Discard survival from set-net fisheries is poorly studied. Trials were conducted on two commercial fishing vessels over seven trips from November to February 2017–2018 in the Baltic Sea. The nylon trammel nets had a nominal bar size for the inner/outer wall of 75/350 mm and 85/400 mm. Soaking time was 23–47 h, water depth 7–18 m, and deck temperature was −0.1–6.0 °C. Following commercial practice, the trammel nets were hauled back onto the vessel, after which netting and fish passed through a net hauler onto a steel sorting table where the entire fish catch were manually untangled by the fishers and plaice collected by scientists. We used a storage system for housing the captured fish inside fishing harbours during observations. Catch-damage-index (CDI) and Reflex Action Mortality Predictor (RAMP) scores were used to assess fish condition immediately after capture and at the end of observation periods. All plaice below 40 cm were sampled with a total number of 118 individuals from 13 fleets (several nets joined together). The fish were assessed for short-term survival for 4–10 days with full survival (100%). The majority of fish exhibited no reflex impairments. Minor bruises, fraying, and net marks were frequently observed on captured fish. The overall condition of the fish did not change during observation periods. • High short-term survival rate in plaice from trammel net fisheries during winter season. • Development of methodology for set-net discard survival studies. • Low Reflex Action Mortality Predictor (RAMP) in trammel net fished plaice. [ABSTRACT FROM AUTHOR]