Article

Benthic disturbance by fishing gear in the Irish Sea: A comparison of beam trawling and scallop dredging

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Abstract

1. The distribution of effort for the most frequently used mobile demersal gears in the Irish Sea was examined and their potential to disturb different benthic communities calculated. Fishing effort data, expressed as the number of days fished, was collated for all fleets operating in the Irish Sea in 1994. For each gear, the percentage of the seabed swept by those parts of the gear that penetrate the seabed was calculated. 2. For all gears, the majority of fishing effort was concentrated in the northern Irish Sea. Effort was concentrated in three main locations: on the muddy sediments between Northern Ireland and the Isle of Man (otter and Nephrops trawling); off the north Wales, Lancashire and Cumbrian coast (beam trawling); the area surrounding the Isle of Man (scallop dredging). 3. In some areas, e.g. between Anglesey and the Isle of Man, the use of scallop dredges and beam trawls was coincident. A comparative experimental study revealed that scallop dredges caught much less by-catch than beam trawls. Multivariate analysis revealed that both gears modified the benthic community in a similar manner, causing a reduction in the abundance of most epifaunal species. 4. Although beam trawling disturbed the greatest area of seabed in 1994, the majority of effort occurred on grounds which supported communities that are exposed to high levels of natural disturbance. Scallop dredging, Nephrops and otter trawling were concentrated in areas that either have long-lived or poorly studied communities. The latter highlights the need for more detailed knowledge of the distribution of sublittoral communities that are vulnerable to fishing disturbance. ©British Crown Copyright 1996.

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... As such, it is exposed to anthropogenic activities which threaten the natural resources found there and the environment itself. Fisheries activity is extensive throughout and particularly intensive in the fine-grained sediment area west of the Isle of Man referred to as the Western Irish Sea Mud Belt (WISMD) Kaiser et al., 1996). The relatively benign setting offered by this area, with its low energy regime and uniform fine-grained substrate, makes it an ideal habitat for many commercially fished species especially the Dublin Bay Prawn (Nephrops norvegicus) and various benthic macrofauna (Kaiser et al., 1996). ...
... Fisheries activity is extensive throughout and particularly intensive in the fine-grained sediment area west of the Isle of Man referred to as the Western Irish Sea Mud Belt (WISMD) Kaiser et al., 1996). The relatively benign setting offered by this area, with its low energy regime and uniform fine-grained substrate, makes it an ideal habitat for many commercially fished species especially the Dublin Bay Prawn (Nephrops norvegicus) and various benthic macrofauna (Kaiser et al., 1996). The depth of the effect of trawling in this area may be up to 20 cm depending on the type of gear used (Kaiser et al., 1996). ...
... The relatively benign setting offered by this area, with its low energy regime and uniform fine-grained substrate, makes it an ideal habitat for many commercially fished species especially the Dublin Bay Prawn (Nephrops norvegicus) and various benthic macrofauna (Kaiser et al., 1996). The depth of the effect of trawling in this area may be up to 20 cm depending on the type of gear used (Kaiser et al., 1996). Studies regarding the effect of trawling in the area have largely focused on the effect it has on species population richness and community changes (Kaiser et al., 1996;. ...
... Located between the Irish and British mainland, the Irish Sea is the focus of increasing socio-economic interest through the development of offshore renewable energy installations (the Irish Government is targeting 3 GW of offshore wind in the Irish Sea by 2030 (DCCAE, 2019) as well as communications and energy infrastructure, such as the CeltixConnect cable and Greenlink interconnector. The Irish Sea is also home to a number of important fishing areas and contains a variety of benthic habitats as a result of its varied seafloor geology (Kaiser et al., 1996;Robinson et al., 2011). The spatial and temporal interaction between hydrodynamical processes and seabed substrate has a profound influence on seafloor evolution with direct implications for a range of offshore activities such as marine engineering, renewable energy, and habitat mapping. ...
... O'Neill and Summerbell, 2011;Palanques et al., 2001). Trawling intensity is most heavily concentrated in the WISMB for the Dublin Bay Prawn (Nephrops norvegicus) (Kaiser et al., 1996;O'Higgins et al., 2019). Whilst sediment mobilisation levels for the WISMB have been calculated to be naturally low, trawling has been shown to have a high impact on sediment disturbance with loss of seabed, sediment coarsening and weakening of sediment shear strength recorded (Coughlan et al., 2015). ...
... e. low sand) for burrow construction (Johnson et al., 2013). Given that the WISMB accounts for 25% of the total Irish Sea seabed trawled from April to December, with up to 55% fishing intensity (Kaiser et al., 1996) further work is required in order to understand the implications of trawling induced sediment mobilisation in this area. This is also true for areas where sediment is more frequently mobilised which are also trawled as induced remobilisation of sediment could similarly alter the habitats of the species being trawled. ...
Article
The seafloor is increasingly being used for siting renewable energy and telecommunication infrastructure as well as supporting key fisheries and biodiversity. Understanding seabed stability and sediment dynamics is, therefore, a fundamental need for offshore engineering and geoscience and biological studies. In this study we aim to quantify the levels of sediment mobility in the Irish Sea: an area of increasing socio-economic interest and subsequent seabed pressures. The temporal and spatial interaction between bathymetry, hydrodynamics and seabed sediments leads to a complex pattern of erosion, bedload transport and deposition which can affect seabed infrastructure and modify habitats. Information on current and wave conditions were obtained from numerical modelling to assess their role in generating seabed hydrodynamic conditions. These outputs were coupled with observed seabed grain-size data to predict the exceedance of sediment mobility thresholds by bed shear stress values for a period of one year according to empirical formulae. Exceedance frequency values were used to calculate a number of sediment disturbance and mobility indexes to allow for a robust assessment of sediment dynamics. Sediment in the Irish sea, on average, is being mobilised 35% of the time during the year, with 35% of the spatial area studied being mobilised over 50% of the time. Even in areas of low sediment mobilisation frequency (<5%), there are implications for bedform dynamics. The spatial patterns of the calculated sediment mobility are discussed in the context of current seabed geomorphology and the implications for both engineering and environmental considerations.
... The Irish Sea is exposed to other human activities that threaten the environment and natural resources. Fisheries activity is extensive throughout and particularly intensive in the fine-grained sediment area west of the Isle of Man, known as the Western Irish Sea Mud Belt (WISMD) (Belderson, 1964; Kaiser et al., 1996). The relatively calm setting in this area, with its low energy regime and uniform fine-grained substrate, makes it an ideal habitat for many commercially fished species. ...
... Prawn (Nephrops norvegicus) as well as various benthic macrofauna (Kaiser et al., 1996). According to Kaiser et al. (1996), the total area of the seabed in the Irish Sea disturbed by otter and Nephrops trawls is between 6013 and 6404 km 2 . ...
... Prawn (Nephrops norvegicus) as well as various benthic macrofauna (Kaiser et al., 1996). According to Kaiser et al. (1996), the total area of the seabed in the Irish Sea disturbed by otter and Nephrops trawls is between 6013 and 6404 km 2 . Of this effort, Nephrops trawling is largely concentrated in the WISMB (which accounts for 25% of the total Irish Sea seabed) from April to December, with up to 55% fishing intensity (Kaiser et al., 1996). ...
... The effects of scallop dredging on marine ecosystems vary with different seabed types, levels of background disturbance, local hydrography, fishing intensity, and the characteristics of the ecological community (Kaiser et al., 1996;Auster et al., 1996;Bradshaw et al., 2001). The following sections address scallop dredging impacts that generally apply to any marine ecosystem. ...
... As scallop dredges can penetrate anywhere between 3 and 10 cm into the seabed (Currie and Parry, 1996;Kaiser et al., 1996), they have a strong potential to disrupt the benthic infauna; the organisms that burrow and live within the sediment. Any impact scallop dredging has upon the infauna can percolate through the entire marine ecosystem as they constitute an important food resource to fish, invertebrates, and other higher trophic levels (Daan et al., 1990). ...
... As discussed earlier, the effects of scallop dredging vary with different seabed types, level of background disturbance, local hydrography, fishing intensity, and the characteristics of the ecological community (Auster et al., 1996;Kaiser et al., 1996;Bradshaw et al., 2001;Harris et al., 2014;LeBlanc et al., 2015). The following sections examine these differences in greater depth. ...
Chapter
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Global landings of scallops have grown dramatically in recent decades and these fisheries are now among the most lucrative in several countries around the world. Despite this apparent success story, concerns have arisen about the wider ecosystem effects of scallop fisheries. This is particularly the case for the most common type of fisheries that use dredges to rake scallops off the seafloor. Here the evidence for negative effects arising from this practice is reviewed and suggestions offered as to ways in which scallop fisheries might be better managed. In general, dredging causes loss of biodiversity and reduces the complexity of benthic habitats by flattening substrates and removing structurally complex species such as hydroids, bryozoans and seaweeds. This is significant because such habitats are key nursery and feeding areas for a wide range of species, including commercially important fish and shellfish. Scallop dredging also catches a variety of more mobile species such as crustaceans, echinoderms, fishes, and in certain areas, sea turtles, which is clearly of concern. Despite these general rules, the magnitude of effects varies considerably in different habitats. The most severe are in biogenic reefs such as formed by maerl and mussels, so there is a strong argument for fully protecting such areas. Reef and cobble habitats also appear relatively susceptible, but soft sediments such as sand, mud and gravel (which are the focus of most scallop fisheries) appear more resilient, particularly in areas adapted to high levels of natural disturbance. Determining the full effects of dredging remains difficult, however, because most fishing grounds have been exploited for decades, long before scientific study began. Long-term protected areas are beginning to provide insights into the recovery and composition of benthic communities in the absence of dredging. Continued study of these areas will be a key to gaining a better understanding in the future. In terms of reducing the ecosystem effects of dredging, an approach that combines effort control, gear modifications, and spatial management is suggested. Spatial management is showing great promise where it has been applied as it can offer a win–win scenario, which protects vulnerable habitats while boosting scallop stocks by providing breeding and nursery refuges; however, spatial management must be carefully planned to maximise biological benefits while accounting for socio-economic factors. Scallop fisheries must also be managed in unison with other fisheries in order to restore diversity and resilience to oceans facing an uncertain future of climate change and growing anthropogenic pressure.
... As king scallops normally live buried within the sediment (Bradshaw et al. 2001), the opening of the dredge is fitted with a spring-loaded bar of 8-9 teeth, each up to 11 cm long and spaced 8cm apart, which are designed to rake scallops out from the sediment and into a dredge net which trails closely behind (Fig. 4b). The teeth on Newhaven dredges penetrate anywhere between 3-10 cm into the seabed depending on seabed type (Kaiser et al. 1996). The spring-loaded tooth bar allows the teeth of the dredge to flex backwards, preventing it from snagging on harder ground and improving catch efficiency. ...
... The spring-loaded tooth bar allows the teeth of the dredge to flex backwards, preventing it from snagging on harder ground and improving catch efficiency. The tension in the springs can also be adjusted to improve the efficiency of the gear on different seabed types (Kaiser et al. 1996). Still, the capture efficiency of Newhaven scallop dredges is quite low -between 5-41 % for legal sized scallops depending on seabed type and operating conditions (Dare et al. 1993;Beukers-Stewart et al. 2001;). ...
... In the UK, each dredge is normally 75 cm in width and the mesh size of the underside "belly" and top nets are generally 80 mm and 100 mm respectively. Typically the belly of the dredge net is constructed of steel rings in order to reduce damage from rough ground (Kaiser et al. 1996). Vessels can tow anywhere between 2 and 22 dredges per side depending on local regulations and vessel power (see section 1.6). ...
Technical Report
Full-text available
The king scallop fishery is the fastest growing fishery in the UK and currently the second most valuable. The UK is also home to the largest queen scallop fishery out of all of Europe. However, concerns have been raised about the effects of this recent growth of UK scallop fisheries among scientists and conservation bodies, as well as amongst the public following recent media campaigns (e.g. Hugh’s Fish Fight). This is because the majority of scallop landings (95%) are made by vessels towing scallop dredges, a type of fishing gear known to cause substantial environmental impacts. In addition, several scallop stocks are showing signs of overexploitation and there is concern over future impacts of ocean warming and acidification. Although, there have been several recent improvements in the management of scallop fisheries in parts of the UK, information on many scallop stocks around the UK is still lacking. This report therefore proposes that better monitoring and stock assessments are needed for these scallop fisheries and stocks. With recent legislation soon to result in the development of a new network of marine protected areas (MPAs) around the UK, and improved management of fisheries in European Marine Sites, now is a crucial time to review the UK scallop dredge fishery and its impacts on the wider environment so that this new legislation can support a sustainable future for the UK scallop fishery. This report was therefore commissioned by the Sustainable Inshore Fisheries Trust with the aim of collating existing knowledge on the management and environmental impacts of scallop fisheries around the UK.
... [40,42,69,84,121,160,162]). Habitats subjected to high levels of natural disturbance are more resilient than structurally complex biogenic habitats which usually are relatively undisturbed by natural perturbations [37,82,162]. In the same line, healthy biogenic habitats composed of long-lived species with higher functional redundancy are more susceptible to physical disturbance than degraded habitats [46,48,126], which is reflected by their own characteristics, biological and functional traits [17,69]. ...
... abundances [37,82,140]. The low species richness and diversity found in habitats on sandy bottoms on the summit of the central guyot (habitats 8-'sand-pennatulids' and SBcirca-Circalittoral soft bottoms) [46] leads us to think that these habitats could be subjected to some kind of natural disturbance acting on the top of the seamount. ...
Article
Physical damage caused by the mechanical impact of bottom fishing gears on epibenthic community can reduce the biomass and coverage of habitat-forming species as well as the richness and diversity of the rest of the associated community. A practical development of a methodology for spatially assessing the potential degree of disturbance that benthic habitats suffered as a consequence of trawling and long-lining was carried out using a seamount located within a marine Natura 2000 site in the western Mediterranean as a case of study. By jointly assessing the extent of the impact and mapping the sensitivity of all the habitats to these fishing activities, vulnerability and disturbance per benthic habitat and pressure type was evaluated. Habitat sensitivity and fishing effort were combined using a disturbance matrix which categorize grid cells in 9 different levels of disturbance. Additionally, different thresholds of probability of presence of the different habitats obtained from distribution models were used to identify priority conservation and potential recovery. Around 50% of the area was disturbed by fishing and all habitats, both biogenic and non-biogenic, were subjected to fishing. Most of the trawling effort was carried out on soft bathyal substrates while the percentage of longlining effort carried out on hard bottoms was relatively higher than for trawling. Biogenic habitats showed significantly greater sensitivity to both trawling and longlining than non-biogenic habitats. Disturbed, priority conservation and potential recovery areas were identified and mapped in order to inform marine spatial planning.
... Scallop dredging may impact the benthic community by reducing densities and shifting spatial distribution of macrofaunal populations (Langton et al. 1987, Langton & Robinson 1990, Kenchington 2000, Bradshaw et al. 2002, by removing colonial epifauna and reducing habitat complexity , Auster et al. 1996, Collie et al. 1997, Collie & Escanero 2000, Hall-Spencer & Moore 2000, and by redistributing grain size of sediments and increasing silt in the water column (Caddy 1989, Mayer et al. 1991, Grant 2000, MacDonald 2000. Unfortunately, many studies do not assess disturbances caused by scallop dredging against a background of natural disturbance that occurs over time (Kaiser et al. 1996, Jennings & Kaiser 1998, Watling & Norse 1998, Auster & Langton 1999). This is difficult and expensive to do, and as a consequence dredge-impact studies are often hampered by the lack of proper environmental-impact assessment and appropriate monitoring , Jennings & Kaiser 1998. ...
... Many studies examining the effects of scallop harvesting on the marine habitat have been conducted in Europe and Australia, where toothed dredges are used to collect the slightly buried scallops (Chapman et al. 1977, Kaiser et al. 1996, Jennings & Kaiser 1998, Hill et al. 1999, Hall-Spencer & Moore 2000, Veale et al. 2000, Jenkins et al. 2001, Bradshaw et al. 2002. The New Bedford offshore sea scallop dredge rides on 2 shoes and skims over the sea floor, flipping the sea scallops with the sweep chains into the chained bag, and may have less impact on the sea floor than a toothed dredge (Bourne 1964, Caddy 1989. ...
Article
Full-text available
On Georges Bank, 2 areas that had been closed to sea scallop fishing since 1994 were opened for a limited harvest from August 2000 to February 2001. The effects of this limited short-term fishery on the epibenthic community were examined using a 'before/after, control/impact' environmental design conducted with video surveys. A centric systematic survey with 1379 stations placed on a 1.57 km grid, with 4 video quadrats collected at each station (3.235 m(2) per quadrat equaling 17 789 m(2) total sample area), was completed in 2 control and 2 impact areas before and after the fishery. The sea scallops Placopecten magellanicus and starfishes (primarily Asterias vulgaris) comprised more than 84 % of the fauna. Changes in the number of taxonomic categories and the density of individuals within each category in the areas impacted by the fishery were similar to changes in the control areas that remained closed to fishing. Further, sediment composition shifted between surveys more than epibenthic faunal composition, suggesting that this community is adapted to a dynamic environment. The limited short-term sea scallop fishery on Georges Bank appeared to alter the epibenthic community less than the natural dynamic environmental conditions.
... Of current fishing practice, meta-analyses studying a wide range of towed bottom-fishing gears suggest that scallop dredging is responsible for some of the most damaging effects to the benthic habitat (Collie et al., 2000;Kaiser et al., 2006). Small-scale studies provide empirical evidence that scallop dredging results in the destruction and removal of many non-target, infaunal and epifaunal species as well as the physical disturbance of the sediment (Eleftheriou and Robertson, 1992;Thrush et al., 1995;Kaiser et al., 1996;Currie and Parry, 1996;Hall-Spencer and Moore, 2000;Hinz et al., 2011). Set alongside this pattern of disturbance, scallop stocks in some of the main fishing areas in Scottish waters have declined over the last decade (Howell et al., 2006;Keltz and Bailey, 2010). ...
... The dredges used are normally of the 'Newhaven' type and are fitted with a spring-loaded tooth bar that allows the dredge to pass over hard ground (Figure 2). The spring loaded action of the toothed bar allows the teeth to flex backwards, preventing the dredge from snagging on harder ground, and also improves the catch efficiency of the dredge (Kaiser et al., 1996). The size of the teeth, their spacing, and the diameter of the mesh rings used to make up the collecting bag all combine to affect the size of animals caught up in the dredge (Eleftheriou and Robertson, 1992). ...
Technical Report
Full-text available
In response to concern over the damaging effects of scallop dredging, there is a readiness among marine planners and conservation organisations to utilise spatial closures as a tool in the management of the fishery. Although primarily used to protect key habitats and species and enhance biodiversity, it is thought that marine protected areas may also help reestablish or enhance stocks. Lamlash Bay, in the Firth of Clyde, was declared Scotland’s first No Take Zone (NTZ) in 2008. The cessation of bottom trawl and dredge fishing in the NTZ provides an excellent opportunity to investigate the re-colonisation of newly protected areas by scallops. This report presents the results of photographic surveys undertaken by Marine Scotland Science in July 2009 and November 2010 during the first phase of a study of the NTZ’s effects. It includes baseline abundance data for the great scallop, Pecten maximus, and the queen scallop, Aequipecten opercularis and a preliminary analysis of densities inside and outside the NTZ. There was insufficient evidence that the NTZ contains higher densities of adult P. maximus or A. opercularis than reference areas sited in adjacent waters, or that abundances within the NTZ increased more rapidly than elsewhere. Given the short time scales involved in this the initial phase of the study, this result is not entirely unexpected as the NTZ is unlikely to have had sufficient time to affect abundance levels. The analyses does suggest, however, that the reference areas chosen to test the performance of the NTZ over time are comparable with the NTZ and that the data collected provide a suitable baseline for a longer term study of changes in scallop abundance within Lamlash Bay.
... This new type of queen dredge differs in its design, compared with the traditional Newhaven dredge, such that it is wider, having a higher front opening and instead of metal teeth it possesses a rubber lip to stimulate queen scallops to swim into the water column such that they are caught up into the metal mesh belly bag. While the impacts of otter trawls and Newhaven type dredges are relatively well known (Kaiser et al. 1996, Kaiser et al. 2006) no knowledge exists about the effects of the newly developed Queen scallop dredge relative to the other Queen scallop gears. ...
... Most of the marine fisheries especially in tropical waters are mixed fisheries, directed at a few commercially target species, while inadvertently capturing a wide variety of non-targeted bycatch species 4,5 . There is a general concern about changes caused in the marine benthic assemblages by the trawlers 6,7 .The first step towards understanding and solving the bycatch problem is to identify and quantify bycatches 4,8 . Gastropod forms a significant non-targeted component in the fishery by trawl fishery and forms an important constituent of the benthic community. ...
... Scallop dredging targeting Pecten maximus (Linnaeus, 1758) and Aequipecten opercularis (Linnaeus, 1758) is thought to have deteriorated M. modiolus aggregations, removing larger epifaunal elements, including the base individuals, in Strangford Lough in the Irish Sea (Brown 1989;Magorrian 1996;Service & Magorrian 1997;Magorrian & Service 1998;Roberts et al. 2004Roberts et al. , 2011Rees 2009;Strain et al. 2012) and off the Isle of Man (Kaiser et al. 1996;Veale et al. 2000;Bradshaw et al. 2002;Lambert et al. 2011). A survey of scallop dredging impacts targeting Chlamys islandica (O.F. ...
Article
The boreal bivalve Modiolus modiolus is common subtidally where it aggregates to form extensive, long-lived, biogenic habitats with a diverse associated flora and, especially, fauna. Despite this ecological importance, M. modiolus has not been described in terms of its functional morphology and overall biology. Modiolus modiolus is a typical epibenthic, suspension-feeding mytilid, albeit with anatomical modifications adapting it to a partially buried, gregarious lifestyle in a stable environment experiencing medium–high energy levels. The juvenile shell is covered partly in byssal setae secreted by the byssal gland and foot complex and becomes covered in sand grains held in place by a mucoid cement secreted by the dorsal mantle. The camouflaged shell at this vulnerable time probably serves as an anti-predator device. Individuals grow to maximum shell lengths of ∼60–213 mm, depending on depth and locality. With age (≥ 20–45 years), shells often become deformed, particularly posteriorly and around the byssal gape, thereby increasing reproductive capacity (gonadal volume) without increasing somatic growth. Information on the biology, reproductive strategy and life history traits of M. modiolus are reviewed. These field- and laboratory-derived data provide us with essential information to aid future research into the protection and conservation of this ecologically important biogenic habitat. This is because, today, dredging and fishery activities using bottom-towed gear have seriously damaged several M. modiolus habitats with deleterious impacts on ecosystem functioning. Post-impact recovery times are slow and dependent on both local and mega-population distributions.
... It is generally accepted that physical disturbance from benthic trawling, such as scallop dredging, impacts both M. modiolus and maerl beds (for examples see Kaiser, et al., 1996;Collie, et al., 1997;Magorrian and Service, 1998;Collie, et al., 2000;Hall-Spencer and Moore, 2000;Bradshaw, et al., 2002). However, it should also be noted that additional natural and anthropogenic factors also have the potential to impact both M. modiolus and maerl beds. ...
Technical Report
Full-text available
Horse mussel (Modiolus modiolus) and maerl beds are ‘priority’ habitats that can be threatened by human activity and as such require conservation under the UK Biodiversity Action Plan (UK BAP). During 2010 the Shetland Shellfish Management Organisation (SSMO), the body responsible for the management of all shellfish stocks within six nautical miles of Shetland, proposed to voluntarily close 24 areas to scallop dredging vessels in order to help conserve these priority habitats. Initially, the boundary of each closed area was defined from data extracted primarily from the Shetland Marine Spatial Plan but also through consultation with local maritime users. Some data were of limited quality, extent, or based on non-validated reports several decades old. In several cases fishermen actively involved in the development of the closed areas questioned whether the priority feature was present in the area at all, based on their local knowledge. Despite such reservations, the science-industry partnership involved agreed to adopt an iterative, precautionary approach whereby areas would be closed pending detailed survey and assessment, and the legalisation of the voluntary closed areas came into force in 2011. The primary aim of this report was to define the effectiveness of the current closed areas based on up-to-date, high resolution survey data so that the SSMO can validate and refine its spatial management plan. Closed areas to scallop dredging are widely distributed around Shetland, amounting to just under 26 km2 of sea surface area. The areas vary in size from 0.003 km2 to 14.6 km2, the largest accounting for 56.6% of the total area closed around Shetland. This variation is primarily due to the type of externally sourced data (i.e. point data or predicted species bed) used to originally define the extent of the feature. Historically, predicted species beds had been derived from a number of sources and various agencies from a combination of point data and localised bathymetry information. The current study surveyed existing closed areas using a hull mounted multibeam system and groundtruthed with an underwater camera system. Information was imported to GIS in order to create a georeferenced map of the presence of the species of interest, and in particular where they occur in sufficient abundance to consitute a ‘priority feature’ or habitat. Although it is generally accepted that the presence of the species does not inidcate a priority feature at low density and/or small patch size, some debate remains as to what criteria should be met to define the presence of a significant feature; a suggested criteria appropriate to the survey methodology was defined for this study. For the 20 sites surveyed in detail the predicted species beds, based on or derived from historical data, were not found to be representative of the current distribution of priority features. As a result the corresponding closed areas originally established by the SSMO were either not fully encompassing the UK BAP habitats located at the sites or were not protecting any UK BAP habitats (none present). Of the 20 sites surveyed, 12 were found to have either M. modiolus, maerl, or both; nine of these contained a priority feature but only two had a closed area which completely encapsulated the full extent of the feature. Alteration or removal of the boundaries of the existing closed areas is therefore appropriate and recommendations for this process are included. Further refinement of boundary areas may be warranted after consultation and additional focussed surveys. Although the surveys illustrate the need for validation of closed areas with high quality acoustic and visual survey data, the exercise provides a practical and successful industry-science approach to the establishment and incremental development of local spatial management plans. In the absence of detailed maps for entire sea areas, which rarely if ever exist, the use of historical data and local knowledge provides a basis for the focussing of survey resources. The use of acoustic surveying technology, such as multibeam, proved highly cost effective in mapping priority habitats. Multibeam surveys cover large areas of seabed relatively quickly, producing good quality maps to a high degree of accuracy, and as with this example, this is ideally suited to management plans based on ‘physical’ features (biogenic reefs) rather than biotopes. However, broad scale mapping of this type may inform the likely presence of biotopes, which can be confirmed by more cost and labour intensive methods if required. Although the science-industry partners acknowledge that the methodology of using historical data and local knowledge may not result in absolute protection of priority features during the first iteration, as is the case here, it was deemed preferable to establish a locally agreed framework, dialogue, and options for further refinement toward this goal than to leave the conservation of priority features unaddressed or awaiting investment in large-scale, holistic marine surveys. Direct stakeholder involvement in the process installed belief that clear and unambiguous science would rectify issues at a later date, and therefore fishermen agreed to voluntary closures of these areas before they were made statutory. As the Scottish Government currently empowers the SSMO to make changes to the spatial management plan for shellfisheries in the waters around Shetland by means of a Regulating Order, further surveys and consultation will increment toward more fine-scale improvements to the appropriateness of the plan well into the future.
... Bottomfishing requires boats designed specifically for power, stability and sailing a steady course, and equipped with specialised gear for raising, lowering and surviving the dragging of heavy nets, and with a crew who know how to work that gear (McKee 1983, 40-41; Rawson and Tupper 2001, 689); its onset marks the emergence of a specialised marine fishing technology from general-purpose fishing. Bottom-fishing damages the sea-bed (Kaiser et al. 1996) and its occupants (Jenkins et al. 2001), including the whelks themselves (Mensink et al. 2000), contributing to their local extermination (Cadée et al. 1995). Therefore, the usual method uses 'pots' of woven wicker or wire, baited with dead fish or carrion (Hancock 1967, 4-6), much like fishing for crab or lobster. ...
Article
Full-text available
Bottom-fishing is a major step in the increase of exploitation of marine resources, requiring specialised craft, technology, and practitioners. However, the onset and development of bottom-fishing is almost impossible to observe directly in the archaeological record, and is usually reconstructed by implication. The shells of common whelk (Buccinum undatum) from a kitchen midden at Carisbrooke Castle, Isle of Wight, southern England, showed a pattern of damage characteristic of harvesting by bottom-fishing, rather than the usual baited pots. Some whelks had survived being dredged several times. The very consistent size-shape relationship made it likely the whelks were all from a single habitat, probably in the fast tidal flows typical of the oyster-beds just north of the island. The whelks were harvested along with oysters: the whelks' shells were encrusted in a similar way to the oysters in the same midden, and the whelks even bore sub-adult oysters (spat), despite these being potential prey for whelks. This may be the first time whelks have been shown to have been harvested along with oysters and also seems the first direct evidence for a bottom-fishery for whelks.
... Subtidal harvesting of bivalves is undertaken using a variety of mechanical fishing techniques. The most widespread of these involves towing gangs of dredges, each a rigid metal framed fishing gear usually fitted with a tooth bar, across the seabed so that the shellfish are excavated from the sediment (Caddy, 1973;Eleftheriou and Robertson, 1992;Currie and Parry, 1996;Kaiser et al., 1996). Another technique, clam kicking, uses the wash of a boat's propeller to fluidize the substratum which makes buried shellfish easier to catch in a net towed behind the boat (Peterson et al., 1987). ...
Article
Surveys were conducted in two shallow bays in the Orkney Islands, UK; Orphir Bay, an unexploited (control) site, and Bay of Ireland, a fished site, to investigate the effects of suction dredging on the resident razor clam, Ensis arcuatus, populations. A lower density and significantly smaller mean length of razor clams were present at the dredged site compared with the control site. The age of individual razor clams was estimated using internal shell microgrowth patterns, visible in acetate peels of polished and etched shell cross-sections. Ensis arcuatus are relatively slow growing animals with the two study populations characterized by old individuals and an obvious lack of juveniles, indicating populations with little resilience to disturbance. An analysis of the shell sections of razor clams from the Bay of Ireland revealed the presence of shell margin breaks, consisting of deep clefts in which sand grains were embedded in the shell matrix, whilst those from Orphir Bay had fewer disturbances to shell growth. It is suggested the disturbances to shell growth are the result of repeated suction dredging operations in the Bay of Ireland. In situ reburrowing experiments were conducted to determine the survival rate of E. arcuatus (<160 mm shell length), returned to the sea after capture and to estimate the indirect effect of dredging on the razor clam population. These individuals displayed a slow initiation of “escape-digging” which rendered them vulnerable to attack from predatory crabs and fish, indicating that there is likely to be a low survival rate of any returned undersized clams or ones that are disturbed and escape from the suction dredge.
... Fishing with bottom towed gears such as beam trawls and scallop dredges impacts populations of by-catch species (Kaiser et al. 1996, Veale et al. 2000, Jenkins et al. 2001, reduces seabed habitat complexity and heterogeneity (Collie et al. 1997(Collie et al. , 2000a, causes shifts in community structure and trophic interactions (Carbines & Cole 2009, Hinz et al. 2009, Strain et al. 2012) and alters the physical structure of the sea floor and biogeochemical processes (Schwing -hamer et al. 1998, Smith et al. 2000, Jennings et al. 2005. The impacts and recovery times post fishing disturbance depend on the magnitude of the fishing disturbance relative to natural disturbance, and the nature of the habitat and species concerned (Collie et al. 2000b, Kaiser et al. 2002, Henry et al. 2006, Lambert et al. 2011. ...
Article
Full-text available
Fishing with bottom towed gear is widely considered an invasive form of fishing in terms of its impacts upon seabed habitats and fauna. Fishery closures or marine protected areas provide baseline conditions against which to assess the response to the removal of fishing disturbance and thus shed light on their use as fisheries management tools. We conducted repeat underwater camera surveys inside a recently established area that is permanently closed to scallop fishing and a seasonally fished area in Cardigan Bay, UK, to test for differences in scallop abundance and epibenthic community structure and to examine recovery processes over a 23 mo study period. Changes in scallop density and epifaunal diversity and community composition were primarily driven by seasonal fluctuations; no differences were found between the permanently closed area and the seasonally fished area. Temporal changes in epibenthic community inside the permanently closed area were not related to recovery processes associated with the cessation of scallop dredging. Sediment composition and bedforms shifted between surveys, suggesting that this community is exposed to a dynamic environment. It is likely that scallop dredging at the present levels of fishing may be insufficient to induce changes large enough to be detected in the presence of strong natural disturbance. We highlight the importance of considering the physical nature and dynamics of the environment and the nature of the species concerned throughout the process of designating closed areas, to avoid negative impacts on fisheries and limited conservation benefits.
... The present study did not investigate the benthic impact of dredging as many studies have covered this subject. In general, areas that are disturbed by mobile gears such as dredges have been found to have a reduced biomass, reduced species diversity and a reduced abundance of most epifaunal species (Currie and Parry, 1996;Kaiser et al., 1996;Collie et al., 1997;Bradshaw et al., 2001) as well as reduced eelgrass distribution (Neckles et al., 2005). Also, disturbance by mobile gears have been associated with changes in the physical structure of the sea bed Parry, 1996, 1999;Langton and Auster, 1999). ...
Article
Dredging blue mussels (Mytilus edulis) and thus removing structural elements, inducing resuspension of sediment as well as reducing filtration capacity, will inevitably affect the ecosystem. The study demonstrates that the impacts of fishing can be reduced through gear developments.A new light dredge was tested on commercial vessels using two different experimental setups. First, a twin haul experiment tested the standard gear (i.e., a Dutch dredge) against the light dredge by fishing the two gears side by side onboard the same vessel. Second, a single dredge experiment tested the absolute performance of the two gears by fishing in areas with a known blue mussel density.Results from the twin haul experiment demonstrate that the weight of sediment retained in the gear per square metre fished is 49% less in the light dredge compared with the Dutch dredge which will reduce resuspension of sediment at the surface. Also, the drag resistance of the light dredge was significantly less (177.1 vs. 202.7 kg m-1). In the twin haul experiment no significant difference was found in the catch per unit effort (CPUE) of the two gears. The single dredge experiment, on the other hand, demonstrated a significant increase in CPUE exceeding 200% when using the light dredge.Seafloor tracks made by the two dredges could not be distinguished by use of side-scan sonar and the tracks were still detectable 2 months after fishing.It was concluded that replacement of the Dutch dredge with the light dredge would reduce the impact of the fishery on the ecosystem by (i) reducing resuspension of sediment, (ii) reducing fuel consumption, and (iii) potentially reducing energy transfer to the sediment through a reduced gear drag resistance. A potential increase in catch efficiency may reduce the area affected.Fishing with the light dredge is discussed in relation to management of Natura 2000 sites. Copyright © 2014 John Wiley & Sons, Ltd.
... In recent decades the wider recognition of the ecosystem effects of fishing activities has led to a shift in fisheries management from a ''single-species approach'' to an ''ecosystem approach'', which is centered on an understanding of the impacts of fishing on speciesÕ interactions and environment (Sciberras et al. 2013). Fishing affects habitat complexity, the physical structure, and chemical processes of the sea floor (Schwinghamer et al. 1998, Collie et al. 2000, Olsgard et al. 2008), populations of bycatch species, community structure, trophic relationships, and production (Kaiser et al. 1996, Veale et al. 2000, Jennings et al. 2001, Hixon & Tissot 2007, Hinz et al. 2009). ...
Article
Full-text available
Biological data were collected in a Patagonian scallop fishing ground, between 39°00' and 39°50' S and between 87 and 130 m depth. During 2007, we sampled the following stations where the trawling exerted could be precisely determined: 11 locations subjected to continuous fishing effort between 1996 and 2006 (continuous fishing effort, 878 commercial tows) and 12 locations subjected to fishing effort between 1996 and 2002 (interrupted fishing effort, 302 commercial tows). Univariate (species richness, Shannon´s diversity index, and Pielou´s equitability index) and multivariate analysis, analysis of variance, and Kruskal–Wallis tests were applied to analyze species composition and biomass. This study reflects the significant higher density of sessile taxa (Porifera and the ascidean Paramolgula gregaria) and two small ophiuroids (Ophiacantha vivipara and Ophiura lymani), all of them conspicuous during the exploratory cruises conducted in 1995, in the sites where fishing effort was interrupted 4 years before the sampling in 2007 than in those sites continuously exploited and discusses the results considering previous knowledge on the damage that the process on board scallopers imparts on invertebrates bycatch.
... The impact of mobile fishing gear on the seabed is related to both the intensity and frequency of fishing (Watling and Norse 1998). The intensity of disturbance created by otter trawls, like those used in the Gulf of Maine shrimp fishery, is considered to be lower than for other types of mobile gear, such as beam trawls and dredges (Collie et al. 2000, Kaiser et al. 1996. The frequency of benthic disturbance in the shrimp trawling fishery is highly variable throughout the course of the year, and between years. ...
Article
Despite the widespread occurrence of trawl fisheries on mud-bottoms, there is limited knowledge concerning the effects of trawling induced disturbance on these habitats and their resident macrofaunal communities. I investigated the cumulative impacts of seasonal commercial shrimp trawling on infaunal habitat and macrofaunal community structure on two mud-bottom fishing grounds in the Gulf of Maine from June 2000 - December 2001. One fishing ground located near the Outer Pumpkin Ledges (Pumpkin) experienced trawling activity during the 2000-2001 fishing season. In contrast, the other fishing ground near Monhegan Island was not trawled during the same period because shrimp abundances were low. Consequently, impacts of trawling reported for the Pumpkin fishing ground are representative of both past and more recent short- term effects of trawling while results reported for the Monhegan are indicative of longer- term, cumulative effects only. To further examine short-term effects on trawling on mud bottom habitat structure, a Before-After Control-Impact (BACI) experiment was carried out at a different location (Thrumcap). Images of infaunal habitat structure obtained by sediment x-radiography showed no evidence of changes in overall structure (as measured by relative sediment density) related to commercial or experimental (BACI) shrimp trawling disturbance; however, excess 2 ' 0 ~ b activity profiles suggest that trawling may affect sediment mixing regimes. Macrofaunal communities on the two fishing grounds exhibited different responses to shrimp trawling disturbance which I attribute to disparities in levels of fishing activity during the 2000-2001 shrimp season. Multivariate community analysis showed that the Pumpkin fishing ground displayed significant differences in macrofaunal community structure compared to adjacent untrawled areas. Abundances of opportunistic polychaete families were higher in the trawled areas while disturbance-sensitive taxa, such as bivalves, were more abundant in the untrawled area. Similar patterns in taxa abundance were not observed at Monhegan. Results from mud bottom fishing grounds suggest that seasonal shrimp trawling disturbance produced at least short-term changes in infaunal community structure, but did not appear to result in long-term cumulative changes. Resilience to trawling disturbance may be due in part to high levels of biological sediment disturbance from high densities of large surface-dwelling megafauna such as lobsters, fishes, and brittle stars. These animals rework sediments to a depth of 16- 17 cm by burrowing, pit-digging and possibly foraging. Sediment reworking by these benthic megafauna creates disturbance that appears to maintain macrofaunal communities in a perpetually low successional state, thereby potentially minimizing trawling impacts.
... Le type de substrat est un des facteurs déterminants de l'amplitude des impacts observés (Kaiser et al.1998). De même, la présence de perturbations naturelles dans le milieu peut mitiger les impacts de la pêche dans un milieu donné (Kaiser et al. 1996, Prena et al. 1999). Le gisement de l'île Rouge est situé dans un secteur fortement soumis à l'action des courants qui se font sentir jusqu'à une grande profondeur. ...
Technical Report
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Many studies have shown that scallop dredging seriously disturb marine substratum. This study is conducted to evaluate the dredging impact on scallop and benthic communities on the Ile Rouge scallop bed, in Saguenay-St-Lawrence Marine Park. Photographic sampling and experimental dredging do not document effects of dredging on benthic communities. However, a decrease in scallop size at landing suggests that dredging could have an impact on the scallop population. The study site, a sandy-gravel substrat with high velocity currents recover in a few months from the impacts of dredging gear.
... For example, in high-energy environments, fishing disturbances may have negligible effects when compared with natural disturbance (Kulbicki et al., 2007;Sciberras et al., 2013). In many cases, mobile fishing gears adversely affect the marine environment (Kaiser et al., 1996;MacDonald et al., 1996;Collie et al., 1997Collie et al., , 2000aKaiser et al., 2006;Lambert et al., 2011). Static fishing gears have widely been assumed to be relatively benign (Eno et al., 2001;Lewis et al., 2009;Shester and Micheli, 2011;Coleman et al., 2013) yet there is limited evidence to support this (Shester and Micheli, 2011) even though these fisheries are substantial; UK landings of species captured using static gears were 86 600 tonnes and worth £173 million in 2014 (MMO, 2015). ...
Article
Habitat and fisheries usage data are key components for ecosystem-based approach to fisheries management (EBFM). Significant gaps in knowledge remain for fisheries-habitat interactions, particularly in inshore fisheries where vessels are <12 m in length. Here, we show changes in inshore fishing effort distribution (<12 m) and habitat use over the decade 2004-2013. Sightings data of fishing vessel activity recorded by the Northumberland Inshore Fishery and Conservation Authority (NIFCA) were combined with landings data to estimate and map potfishing activity between 2004 and 2013. Spatial temporal changes were investigated using Monte Carlo simulation of randomly sampled fishing effort maps. High resolution (1 m) broadscale (EUNIS level 3) predictive habitat maps of the Coquet to St Marys' Marine Conservation Zone (CQSM MCZ) were used to investigate spatial temporal changes in fishers' habitat selection using compositional analysis. Fishing effort in Northumberland increased between 2004 and 2013 (233 642-354 193 pots year⁻¹). Fishing effort distribution differed between individual years, decreasing over large areas between 2004 and 2007, followed by increases, especially inshore, between 2008 and 2013. Fishers in the CQSM MCZ showed a preference for rocky habitats over sediment habitats. Habitat preference did not vary between years although all habitats experienced increasing fishing pressure. Spatial temporal changes in fishing effort and habitat use were discussed in relation to EBFM. © 2017 International Council for the Exploration of the Sea. All rights reserved.
... Dredges are amongst the most impacting gears on benthos, as they are designed to penetrate the seafloor to capture molluscs. They are heavy and so have a high mechanical impact and associated mortality and they cause high post-capture damage and mortality in the net (Kaiser et al., 1996). Penetration of the dredge teeth varies with the nature and compaction of the deposits. ...
Article
Full-text available
The project Fisheries Measures in Protected Areas (FIMPAS) aims to introduce fisheries measures in the marine Natura 2000 sites within the Exclusive Economic Zone of the Dutch part of the North Sea by the end of 2011. The FIMPAS project covers three such areas, the Dogger Bank and the Cleaver Bank (both to be designated for protection under the Habitats Directive) and the Frisian Front (to be designated for protection under the Birds Directive). These sites are beyond the Dutch 12 nm zone and several EU Member States fish within these areas. Therefore fisheries measures must be implemented through the Common Fisheries Policy. These marine protected areas, as well as the potential fisheries measures, are a consequence of the implementation of the European Birds and Habitats Directives and will be proposed to the European Commission by the Dutch government. The Dutch Ministry for Agriculture, Nature and Food Quality (LNV), together with Dutch environmental NGOs and the Dutch fishing industry, are cooperating within the FIMPAS project to develop the necessary fisheries measures to achieve the conservation objectives for the Dutch Natura 2000 sites of the North Sea. LNV has asked the International Council for the Exploration of the Sea (ICES) to organize the necessary scientific processes and give advice on the desired fisheries measures involving the relevant stakeholders in this process.
... Subtidal harvesting of bivalves is undertaken using a variety of mechanical fishing techniques. The most widespread of these involves towing gangs of dredges, each a rigid metal framed fishing gear usually fitted with a tooth bar, across the seabed so that the shellfish are excavated from the sediment (Caddy, 1973;Eleftheriou and Robertson, 1992;Currie and Parry, 1996;Kaiser et al., 1996). Another technique, clam kicking, uses the wash of a boat's propeller to fluidize the substratum which makes buried shellfish easier to catch in a net towed behind the boat (Peterson et al., 1987). ...
Article
Full-text available
Surveys were conducted in two shallow bays in the Orkney Islands, UK; Orphir Bay, an unexploited (control) site, and Bay of Ireland, a fished site, to investigate the eVects of suction dredging on the resident razor clam, Ensis arcuatus, populations. A lower density and significantly smaller mean length of razor clams were present at the dredged site compared with the control site. The age of individual razor clams was estimated using internal shell microgrowth patterns, visible in acetate peels of polished and etched shell cross-sections. Ensis arcuatus are relatively slow growing animals with the two study populations charac- terized by old individuals and an obvious lack of juveniles, indicating populations with little resilience to disturbance. An analysis of the shell sections of razor clams from the Bay of Ireland revealed the presence of shell margin breaks, consisting of deep clefts in which sand grains were embedded in the shell matrix, whilst those from Orphir Bay had fewer disturbances to shell growth. It is suggested the disturbances to shell growth are the result of repeated suction dredging operations in the Bay of Ireland. In situ reburrowing experiments were conducted to determine the survival rate of E. arcuatus (
... Fishing activity depends on the abundance of target fish as well as weather conditions. Kaiser et al. [51] also found the highest density of trawling activity in early summer to summer due to the opening fishing season in the Irish Sea. In the German EEZ, the largest catches of plaice and sole (targeted by TBB and OTB) are mostly observed within the 3rd and 4th quarter of the year [22]. ...
Article
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The anthropogenic impact in the German Exclusive Economic Zone (EEZ) is high due to the presence of manifold industries (e.g., wind farms, shipping, and fishery). Therefore, it is of great importance to evaluate the different impacts of such industries, in order to enable reasonable and sustainable decisions on environmental issues (e.g., nature conservation). Bottom trawling has a significant impact on benthic habitats worldwide. Fishing gear penetrates the seabed and the resulting furrows temporarily remain in the sediment known as trawl marks (TM), which can be recognized in the acoustic signal of side-scan sonars (SSS) and multibeam echo sounders (MBES). However, extensive mapping and precise descriptions of TM from commercial fisheries at far offshore fishing grounds in the German EEZ are not available. To get an insight into the spatial patterns and characteristics of TM, approximately 4800 km 2 of high-resolution (1 m) SSS data from three different study sites in the German EEZ were analyzed for changes in TM density as well as for the geometry of individual TM. TM were manually digitalized and their density per square kilometer was calculated. In general, TM density was highest in August and October. Moreover, different gear types could be identified from investigating individual TM in SSS data. Beam trawl marks were observed to have widths of up to 22 m whereas otter board marks showed widths up to 6 m. The persistence of TM was estimated to 2-7 days minimum for all three sites based on the SSS data from 2015-2019. A maximum persistence could be defined at one site (Dogger Bank) and it was five months for the investigation period 2016-2017. Besides the main factors driving TM degradation (wave-base impact, sediment-type), different methods for TM detection (SSS, MBES, underwater video) are discussed. The study provides valuable information on the physical impact of bottom trawling on the seabed and can support existing monitoring strategies.
... Brown crabs have previously been reported to be caught more frequently by scallop dredges than trawls (Kaiser et al., 1996). The different catchabilities of the gears may be related to the different types of operation, including the way these gears interact with the sediment and the towing speed (higher in the trawl survey). ...
Article
Brown crab (Cancer pagurus) is a widely distributed crustacean that occurs around the British coastline supporting important commercial fisheries. The habitat preferences of brown crab around Scotland are poorly documented and for the purposes of stock assessment, the species is considered data-poor. Based on an analysis of dredge and trawl surveys taking place in the North Sea (2008–2018), we describe the spatial distribution of brown crab and for the first time, develop abundance and recruitment indices for the species. We make use of geostatistical methods and apply generalized additive models to model catch rates in relation to a number of explanatory variables (depth, distance to the coast, sediment type and year). The dredge and trawl abundance indices were correlated showing a similar trend of increasing catch rates in the early years of the time series up to 2016 and a subsequent reduction. The recruitment index showed a gradual increase in captured juvenile crabs up to 2014 followed by a steep decrease with 2018 being the lowest value estimated. The derivation of robust indicators of stock abundance will contribute to the stock assessment of this species and enable the provision of improved fisheries management advice for brown crab around Scotland.
... Biota-biota dasar yang umum tertangkap oleh garok adalah dari kelompok bivalvia, gatropoda, krustasea, dan cephalopoda. Karena sifat operasi yang aktif (mirip trawl) mencari (mobile) maka potensi jenis tangkapan akan lebih tinggi dari yang pasif (Kaiser et al., 1996). Selain itu, karena memiliki jeruji besi yang menancap ke substrat, maka biota yang hidup pada kedalaman kurang dari 10-15 cm dan bersifat melubang (borrowing) sebagiannya masih tertangkap (Solerio et al., 2008). ...
Article
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Garok is a fishing gear that operates at the bottom or surface of the substrate that is caught of various benthic species. The garok gear that operates in sediment, even in the long term can cause changes in the composition of the biota. Because exploitative fishing proses, can cause damage, vulnerability and at the long-term impact to the sustainability of the population. The research was carried out in Kronjo Bay, Tangerang from March to May 2011. The samples were collected from the operation, then determined the species, quantity, and weight of each species. Descriptive statistical analysis and ANOVA were used to determine the significance of the composition between stations and observation times. The caught consist of Placuna placenta, Anadara, Murex, Tellina, and crustaceans which belong to the mollusk and crustacean groups. Statistical analysis did not show a significant difference between the research stations, but it was significantly based on the observation time with Fhit 3,1 and Ftab 1,7. It turned out that the abundance of basic biota was found to be high in April then decreased in May. Likewise, the abundance did not show a significant difference in the location and time of observation. The catch composition on the Kronjo coast is dominated by the gastropod group with an average composition of above 50% per operation. Keywords: Garok Composition Demersal Kronjo Coastal ABSTRAK Garok adalah alat tangkap yang dioperasikan di dasar perairan yang menangkap berbagai jenis biota dasar. Alat garok yang dioperasikan dapat menangkap beragam jenis biota dasar dan dalam jangka lama dapat menyebabkan terjadinya perubahan komposisi biota. Alat tangkap yang bersifat eksploitatif dapat menyebabkan kerusakan, kerentanan sehingga menganggu keberlanjutan populasi secara jangka panjang. Penelitian dari praktek penggunaan alat garok ini dilakukan di Teluk Kronjo Tangerang mulai Maret-Mei tahun 2011. Sampel dikumpulkan secara eskploratif dari operasi alat garok, kemudian tentukan jenis, jumlah dan bobotnya dari setiap jenis. Analisis statistik deskriptif dan ANOVA digunakan untuk mengetahui perbedaan komposisi antar stasiun dan antara waktu pengamatan. Hasil tangkapan terdiri dari jenis Placuna placenta, Anadara, Murex, Tellina, dan krustasea yang termasuk kelompok moluska dan krustasea. Analisis statistik tidak menunjukan perbedaan yang nyata antara stasiun penelitian, namun berbeda nyata berdasarkan waktu pengamatan dengan Fhit 3,1 dan Ftab 1,7. Kelimpahan biota dasar ditemukan tinggi pada bulan April kemudian menurun pada bulan Mei. Begitu juga kelimpahan tidak menunjukan perbedaan yang nyata pada lokasi dan waktu pengamatan. Komposisi tangkapan di pesisir Kronjo didominasi oleh kelompok gastropoda dengan komposisi rata-rata diatas 50% setiap kali operasi. Kata kunci: Garok Komposisi Demersal Kronjo Pesisir
... Towed gear fisheries Numerous studies and reviews have now examined the effects of towed gear scallop fisheries on the wider environment (Eleftheriou & Robertson 1992, Currie & Parry 1996, Kaiser et al. 1996, Jennings & Kaiser 1998, Hill et al. 1999, Bradshaw et al. 2000, Collie et al. 2000, Hall-Spencer & Moore 2000, Kaiser et al. 2000a, Veale et al. 2000b, Bradshaw et al. 2001, Jenkins et al. 2001, Watling et al. 2001, Bradshaw et al. 2002, Thrush & Dayton 2002, Lart 2003, Broadhurst et al. 2006, Gray et al. 2006, Sheppard 2006. The particular concern arising from many of these studies is that scallop dredges are considered to be among the most damaging of all fishing gears to benthic communities and habitats (Collie et al. 2000, Broadhurst et al. 2006. ...
Technical Report
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Fisheries for scallops, particularly the great scallop Pecten maximus and to a lesser extent the queen scallop, Aequipecten opercularis, are of considerable economic importance to the United Kingdom (UK) fishing industry. Landings of great scallops have been growing steadily since the 1970s and now consistently place this fishery in the top five most valuable species in the UK. Queen scallop catches have been much more variable over the same time period. Great scallops are predominately taken using Newhaven scallop dredges while queen scallops are mostly captured with otter trawls. A very small percentage (< 5 %) of the great scallop catch is taken by hand by SCUBA divers. There are no catch limits on UK scallop fisheries and licence number restrictions are widely regarded as ineffective. Instead great scallop fisheries are mostly managed through minimum sizes, restrictions on dredge number and seasonal closures in some regions. The use of towed fishing gear (dredges and trawls) is also prohibited in a few small areas, generally for conservation purposes. There are few management measures for queen scallops. UK fisheries for great scallops appear to be stable at present, but there is considerable evidence that their productivity could be improved dramatically by better management. This is because at present the fishery has a number of negative effects on juvenile scallops and provides few spawning refuges for replenishment of stocks. The use of towed fishing gear also damages much of the habitat that is crucial for the settlement and survival of young scallops. The negative effects of towed fishing gear, particularly scallop dredges, on benthic habitats and communities are also of considerable conservation concern. In general, areas subject to high fishing pressure tend to lose structural complexity and have lower biodiversity, species richness, species abundance and rates of benthic production. Biogenic reefs / substrates are the most sensitive to disturbance, followed by sandy / gravel areas. However, sandy / gravel substrates have strong potential for recovery if protected. Shallow, sandy areas subject to high levels of natural disturbance are more resilient to fishing disturbance, but tend to support few scallops and lower diversity of benthic species in general. Scallop fisheries also have a high by-catch of mobile benthic species such as crabs, starfish and some fish species. Although the ecological significance of this bycatch is unclear it has the potential to negatively affect crab fisheries. A new management regime for UK scallop fisheries that provided better protection to key scallop nursery and breeding areas, and maintained healthier benthic ecosystems in general would undoubtedly result in more productive and sustainable fisheries. We therefore examined a series of well managed scallop fisheries from around the world to glean how this might be achieved. These fisheries provide good insight into successful management practices for scallops. In Australia the Queensland scallop fishery was incorporated into the Management of the Great Barrier Reef Marine Park as a whole showing that an ecosystem level approach is feasible. In fisheries such as the US sea scallop where the stock was officially declared overfished, reduction in fishing effort resulted in a return to healthy biomass levels. This has included improvement of the size class structure, a characteristic which would be of great benefit to the UK fishery. Protection of juveniles has proven to be a key factor in several cases and in the French fishery in the Bay of Saint Brieuc it was considered a main reason for their success by increasing the number of virgin (previously undisturbed / captured) scallops and therefore the yield per recruit. Habitat mapping has proven invaluable in most examples for providing information on the location of areas that should be protected for the benefit of juvenile scallop settlement and nursery grounds for other commercial species as well as habitat types that should be protected in their own right to conserve biodiversity. There appear to be two successful ways of implementing these changes. One way is with firm government legislation, which includes tight fishing restrictions that is backed up by a strong enforcement plan. This would include measures such as satellite tracking, patrol boats, on board observers and dockside monitoring. An alternative strategy would be to confer on the fishers a level of ownership of their resource and in some cases this has lead to an industry funded and managed recovery of the resource. This strategy ultimately requires little policing. We suggest a UK management plan primarily based on conferring a level of ownership to fishers operating within the 6 mile zone. This may be met with some resistance in the first instance and we would envisage that a level of enforcement may be required at first. This has been found in other examples but as time passes less enforcement is necessary. This should be set within a framework of zones that should consider all users. We further suggest that all interested parties should be included in an ecosystem level management plan and that the scallop fishery should fit into that plan. Provision should be made to minimize the negative effects of one user group on another such as scallop dredges damaging crabs and tangling in crab pots. The inshore area up to 3 miles should be considered a low impact zone with the 3-6 mile area being a medium impact zone. The low impact zone would include fully protected areas, areas just for static gear fisheries (e.g. crab fishers) and scallop divers and other low impact uses such as recreation. Most of the inshore scallop fleet which uses dredges or trawls should operate within the medium impact zone. The larger vessels in the nomadic offshore fleet should operate outside 6 miles. The key to the success of this scheme for the scallop fishery would be to improve the productivity by increasing spawning stock biomass and improving the size class structure of the populations. Recommended management measures include reducing fishing effort, increasing minimum dredge belly ring size and protecting juveniles and key habitats. If these measures were to be put in place, the UK scallop industry has the potential to provide a much more profitable and stable income for its stakeholders.
... Most of the marine fisheries especially in tropical waters are mixed fisheries, directed at a few commercially target species, while inadvertently capturing a wide variety of non-targeted bycatch species 4,5 . There is a general concern about changes caused in the marine benthic assemblages by the trawlers 6,7 .The first step towards understanding and solving the bycatch problem is to identify and quantify bycatches 4,8 . Gastropod forms a significant non-targeted component in the fishery by trawl fishery and forms an important constituent of the benthic community. ...
Article
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Gastropod resource distribution and seasonal variation was studied from 2007-2010 based on onboard collection from multiday trawlers operating in Konkan Malabar region along the eastern Arabian sea at various depth (0-50 m, 51-100 m and 101-200 m), for a total of 619 fishing days (32 months). Thirty five species belonging to 18 families and 4 orders were found in different depths. Family Muricidae dominated in all the depth zone. In 0-50 m depth Tibia sp. (45%) dominated, while Turris sps (19.7%) in 51-100 m and Conus sp. in 101-200 m. Highest diversity (Shannon Weiner H (log 2) was found in 0-50 m depth during post-monsoon season and lowest (1.36) in 101-200 m depth. Gastropod of common occurrence in all the depth zones constituted of six species viz., Bursa sp., Conus sp., Turris sp., Tibia sp., Natica sp., and Murex sp. Bursa sp., made major contribution to the similarity in 50 m, Murex sp. in 100 m and Strombus sp.in 200 m. Tibia sps made the largest contribution to the dissimilarity between 50 m and 100 m depth zone in between groups analysis, while Strombus sp. contributed to the difference between 100 and 200 m depth zones. When considering the season as factor, Bursa sp., Murex sp., and Tonna sp., makes the major contribution to similarity between premonsoon, postmonsoon and monsoon respectively. Dissimilarity between premonsoon and postmonsoon is contributed by Turris sps, while Tonna sps contributes to dissimilarity between premonsoon and monsoon season and Tibia sp., contributed to post monsoon and monsoon season. Introduction Discarding is a common practice in fisheries world over, accounting for an estimated 8% of the annual commercial fish catches amounting to 7.3 million ton of fish returning back to the sea
Article
The North Sea has been subjected to fishing activity for many centuries. However, improvements in both fishing vessels and trawling gears since the early 1900s have meant that fishing intensity has increased. A resultant increase in the areas trawled and the use of heavier and potentially more destructive gears probably had effects on the marine community. Information on benthic communities within the North Sea, from both published and unpublished sources, has been compiled to provide a long-term data set of changes in the marine benthos on five selected fishing grounds over 60 years. In two of these (Dogger Bank and Inner Shoal), there was no significant difference in community composition between the early 1920s and late 1980s. In the remaining three areas (Dowsing Shoal, Great Silver Pit, and Fisher Bank) significant differences were observed. However, these were the result of changes in abundance of many taxa rather than large-scale losses of sensitive organisms. These results suggest that fishing has influenced benthic communities in the North Sea. The possibility remains that fishing-induced changes had occurred at the Dogger Bank and Inner Shoal prior to the 1920s.
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The use of shell damage records as an in situ indicator of past fishing disturbance was investigated using the dog cockle Glycymeris glycymeris L. Shell sections of dog cockles collected from four areas subjected to varying levels of fishing disturbance were examined for the presence of damage records or shell ‘scars’. Animals from a heavily fished area had significantly higher levels of scarring than those from three lightly fished areas. From an estimation of the age of the shells (from internal growth lines and dating of each line), the year in which scarring occurred was determined and this was compared to yearly records of fishing effort. There was a weak but significant positive correlation between the frequency of shell scars per year and the intensity of fishing effort. Our data suggest that whilst scarring in shells of G. glycymeris cannot accurately be used to estimate past fishing intensity on a year-by-year basis, it can be used to differentiate between severely impacted and lightly fished areas of the sea bed.
Article
Most experimental studies on the effects of trawling on the benthos use remote sampling techniques and are conducted in recently trawled areas. Thus it is difficult to determine the effects of trawling on previously unfished areas, and the fates of individual animals cannot be followed. In this study, I follow the fates of individuals of several sessile taxa when exposed to experimental trawling in areas that have not been trawled for some 15-20 years. Although there was a significant trawling by location effect for all multivariate analyses and most individual taxa, I found that trawling had an overall negative effect on the benthos. Epifauna at trawled sites decreased in abundance by 28% within 2 weeks of trawling and by another 8% in the following 2-3 months (compared with control sites). Seasonal seagrasses were also less likely to colonise trawled sites than untrawled sites. The persistence of most taxa declined significantly in trawled areas compared with untrawled areas. In contrast to this, the recruitment rates of several taxa into visible size classes increased after trawling, presumably because of a reduction in competition.
Article
Eight species of sea stars were found in commercially important beds of Iceland scallop, Chlamys islandica, in the southeastern Barents Sea. The population density and size structure of the most abundant species of sea stars were studied in the period 1991-1999. During this period, the density of Asterias rubens increased by a factor of 20-50 and the proportion of large specimens (arm radius >100 mm) increased too. Variations in population density and size structure of other species of sea stars were smaller. A. rubens feeds mainly on molluscs and its population increase was probably related to increased food availability due to damage of bottom fauna by scallop dredging.
Article
Field observations by divers indicated that a high rate of predation of whelks (Buccinum undatum) by starfish (Asterias rubens) occurred in an area disturbed by scallop dredging, although these whelks mostly appeared to be alive and externally undamaged. The ability of whelks to escape from starfish was tested in the laboratory after they were dropped or rolled to simulate direct physical contact with bottom fishing gear. Dropping whelks did not significantly affect their escape behaviour, but whelks which had been rolled took significantly longer to right themselves and were significantly less likely to perform an escape response than whelks that had not experienced this treatment. This study suggests that demersal fishing may indirectly increase whelk mortality by increasing their risk of predation.
Article
The aggregation and feeding behaviour of invertebrate scavengers in areas disturbed by trawling was investigated at three different localities. At each site a fishing disturbance was created using a commercial 4 m beam trawl and scavenger density was quantified using a light beam trawl. At one site two diver surveys were also carried out; along a line fished with a scallop dredge or a beam trawl on two separate occasions. For all experiments the fished and adjacent unfished control areas were sampled before, and at intervals after, the initial fishing disturbance. Sampling with the light beam trawl revealed that hermit crabs Pagurus bernhardus moved into areas which had been fished with a 4 m beam trawl at an experimental site near Anglesey. The density of these hermit crabs increased significantly in the fished area after fishing had taken place, but no change in density occurred in the adjacent control (unfished) area. At two other sites (Red Wharf Bay, Anglesey and a site offshore from Walney Island) there were no detectable increases in scavenger numbers in the fished areas. Furthermore, at the site near Walney Island, numbers of hermit crabs P. bernhardus, swimming crabs Liocarcinus depurator and starfish Asterias rubens actually decreased after fishing. Thus the responses of scavengers to towed fishing gears varied considerably between different communities. At Red Wharf Bay, divers observed similar responses of scavengers to both beam trawl and scallop dredge disturbance. Four predatory species were observed feeding in the fished area; starfish A. rubens, hermit crabs P. bernhardus, brittlestars Ophiura ophiura and whelks Buccinum undatum. These predators fed on damaged bivalves, echinoderms, crustaceans, whelks and polychaetes. The proportion of starfish feeding in the fished area was significantly higher after fishing had taken place. Demersal fishing activities provide food for scavengers in the form of damaged animals which are left in the tracks of the trawl or dredge. The responses of scavengers to fishing disturbance are not always manifested as a large increase in their abundance. It is clear that the magnitude of response varies between species and between habitat types.
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The Malindi–Ungwana Bay fishery Kenya is one of the most important marine fisheries of the Western Indian Ocean. There are two fishing grounds: Formosa and Malindi, with a designated 5-nM no-trawl zone offshore. However, the fishery was faced with numerous resource use conflicts and a decline in catches, culminating in a trawl ban in 2006. This study analyses catches and fishery dynamics before and after the 2006 trawl ban. Results show that artisanal landings declined before the ban, but rapidly recovered within 2 years after the ban was imposed. However, shrimp landings in the artisanal fishery remain low. Commercial shrimp landings gradually declined before the ban: ~550 t in 2001 to 250 t in 2006, and the shrimp: fish bycatch ratio was 1:1.5 compared to early reports of 1:7 in 1999. SIMPER analyses shows that 6 and 16 families (groups) accounted for 91.0 and 90.2% of the similarity in catch within the Formosa and Malindi fishing grounds, respectively. Formosa was important for Claridae, Cichlidae and Protopteridae, while Malindi recorded Carangidae, Siganidae, Carcharhinidae and Lethrinidae as the main families. Future studies should therefore embark on analyses of the factors driving the spatio-temporal distributions of the species and assess the impacts of bottom trawling on fishery dynamics before the trawl ban can be lifted.
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Striped venus (Chamelea gallina) is one of the most important fish resources on the west coast of the Adriatic Sea. Recently, there has been a widespread die-off of C. gallina populations in Friuli-Venezia Giulia (northern Adriatic Sea, Italy), probably due to unfavorable climatic events. Overall, wild populations have become increasingly rare due to many factors affecting the ecological balance of the species. In this study, the available literature was reviewed to determine the current state of knowledge on the biology, ecology, fisheries, and status of C. gallina populations with reference to populations in Friuli-Venezia Giulia. However, few data are available in terms of peer-reviewed articles; much of it can be found in the gray literature (e.g., project reports, ministerial reports, institutional websites, etc.). However, a critical review of the sources reveals that the species is as endangered as the habitats it inhabits. As a result, conservation and restoration efforts have been undertaken to date as part of some larger project to protect the species. Therefore, considering the ecological and economic importance of this species, the results of the new studies will be useful for the scientific community and will be a key element in the conservation of this species.
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During 2010 a set of 22 voluntary closed areas, distributed around Shetland, were proposed by local industry in order to help protect and conserve threatened habitats from potential physical disturbance from scallop dredging. Initially, closed areas were implemented on a precautionary basis over predicted beds of maerl and horse mussel (Modiolus modiolus) derived from historical data. Horse mussel and maerl beds are classed as priority habitats which have been identified as being threatened and requiring conservation under the UK Biodiversity Action Plan (UK BAP). Legalisation of the voluntarily adopted closed areas occurred in 2011. Detailed surveys were conducted to map each closed area with specific reference to the defining features located within. Closed areas were surveyed using a hull mounted multibeam system and ground-truthed with an underwater camera system. Information was imported to a Geographic Information System (GIS) in order to create georeferenced habitat maps of the two species of interest. The appropriateness of each closed area was assessed and a proposed methodology and procedure outlined for any future closed areas. The primary aim was to provide information on which to test the validity of initial closed area boundaries and subsequently allow managers to refine and add to them in the future. The survey illustrated the need to have good quality acoustic and visual survey work undertaken whenever areas have been closed based on historical data and/or predicted habitats. Predicted beds were not found to be representative of the survey findings. The survey highlighted the lack of good quality, robust, accurate, and up to date species information for the waters around Shetland, especially with regard to priority marine features. Although some were neither fully protecting the UK BAP habitats they were designed to protect nor were protecting any UK BAP habitats, a degree of protection had been conferred to some priority features in the first iteration of implementation of closed areas. Survey data were subsequently used to legally alter the closed area boundaries to more appropriately reflect the distribution of priority features. Recommendations were made on appropriate procedures for defining a species bed and on the wider implications of the study’s findings for other fisheries areas developing spatial management plans.
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Bundy, A., Shannon, L. J., Rochet, M-J., Neira, S., Shin, Y-J., Hill, L., and Aydin, K. 2010. The good(ish), the bad, and the ugly: a tripartite classification of ecosystem trends. – ICES Journal of Marine Science, 67: 745–768. Marine ecosystems have been exploited for a long time, growing increasingly vulnerable to collapse and irreversible change. How do we know when an ecosystem may be in danger? A measure of the status of individual stocks is only a partial gauge of its status, and does not include changes at the broader ecosystem level, to non-commercial species or to its structure or functioning. Six ecosystem indicators measuring trends over time were collated for 19 ecosystems, corresponding to four ecological attributes: resource potential, ecosystem structure and functioning, conservation of functional biodiversity, and ecosystem stability and resistance to perturbations. We explored the use of a decision-tree approach, a definition of initial ecosystem state (impacted or non-impacted), and the trends in the ecosystem indicators to classify the ecosystems into improving, stationary, and deteriorating. Ecosystem experts classified all ecosystems as impacted at the time of their initial state. Of these, 15 were diagnosed as “ugly”, because they had deteriorated from an already impacted state. Several also exhibited specific combinations of trends indicating “fishing down the foodweb”, reduction in size structure, reduction in diversity and stability, and changed productivity. The classification provides an initial evaluation for scientists, resource managers, stakeholders, and the general public of the concerning status of ecosystems globally.
Article
1. Man has increased the input of carrion to marine communities worldwide through the practice of discarding fisheries-derived material. A large proportion of discarded material sinks to the sea bed and becomes available to benthic scavengers. Carrion from fisheries discards will subsidize marine food webs, which can sometimes result in the enhancement of consumer populations. 2. This study examines the benthic scavengers that feed on fisheries discards in three habitats in the Irish Sea. We investigated the relationship between the abundance of scavengers feeding on carrion in terms of numbers of each species and the density of those scavenger species in the surrounding area. 3. Observations with bailed time-lapse cameras at a site offshore From Anglesey showed that the hermit crab Pagurus bernhardus was attracted to carrion in greatest abundance and aggregated at densities of up to 330 m(-2). At Red Wharf Bag, a wider range of species was observed: starfish Asterias rubens, hermit crabs P. bernhardus, whelks Buccinum undatum and swimming crabs Liocarcinus spp. There was relatively little scavenging activity at the Walney Island site where the edible crab Cancer pagurus appeared to consume the greatest proportion of the carrion. 4. Numbers of each scavenger species at the bait were only partially related to the background population density of each species at each site. The rate of consumption of carrion varied between sites and could be related to the abundance of different scavenger species at the bait. 5. Baited traps were used to investigate those benthic scavengers that were too small to be observed by time-lapse photography. The traps caught a variety of amphipod and isopod species. Some species were habitat-specific, whereas others were ubiquitous, but specialized in eating a particular type of carrion; for example, Orchomene nanus, which was only caught in traps baited with crab. 6. The results demonstrated that the responses of scavengers to fisheries discards varied between different habitats. The responses of hermit crabs, P. bernhardus, were particularly variable, with large aggregations of individuals occurring at one site but not at others, despite similar background population densities.
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In Egypt due to the Nile delta and the presence of large shallow waters (0-20 m), with areas composed of sand and mud, there could be a great potential for the exploitation of a variety of clams. Given the big gap in knowledge on clams in Egypt the FAO EastMed project has started a study to support Egypt in exploring the possibility to determine if the clam resources exists, and then assist Egypt in developing a potential fishery. The study was conducted between Rasheed and Burullus, where there is a large extend of 60 km of shallow water sandy bottoms. The depth was decided to be limited to 10 m depth contour and target the main potential stock present, that of the clam Chamelea gallina. In total 126 hauls were conducted covering a coastline of about 60 km from 3 - 10 m in depth. All the species sampled were counted and weighed and Chamelea gallina samples were also kept for further processing in the laboratory, where the collection of stock parameters, microbiological and heavy metal analysis were conducted. Overall the results show that the commercial clam Chamelea gallina has a potential for exploitation together with other potentially commercial species such as the changeable nassa Nassarius mutabilis and the bivalve Anadara polii. Most of the biomass is located on the Western side of the area investigated and close to the fishing port of Rasheed, making the area more easily reachable. The results obtained from the bacterial and heavy metal analysis show that the clams are in general within safe limits especially in the western and middle parts of the investigated area and when compared to other commercially exploited bivalve species in Egypt such as Tapes decussatus. In the investigated area when considering the MSY and the cost structure of small trawlers the recommendation is that as a start 10 hydraulic dredgers would be suitable to exploit the fisheries resources. Most of the potential production would probably be for local consumption in Egypt, since export is rather difficult due to the special regulations for the import of bivalve species. The main constraint for the commercialisation of the products will be the market, since these species are at present not commercialised in Egypt, market strategy should be devised in order to successfully introduce the product in the local markets. Once the market has been understood and the products are successfully introduced an EAF management plan could be drawn up.
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It is estimated that within the UK exclusive economic zone (UK EEZ), 524 Mt of organic carbon (OC) is stored within seabed sediment. However, the stability and potential vulnerability of OC in these sediments under anthropogenic stressors, such as bottom trawling activity, remains poorly quantified. To improve our understanding of the areas where sedimentary OC is likely to be at greatest risk from trawling events, we have developed a carbon vulnerability ranking (CVR) to identify areas of the seabed where preventative protection may be most beneficial to help maintain current OC stocks while further research continues to shed light on the fate of OC after trawling (e.g., remineralization, transport, and consumption). Predictive maps of currently available fishing intensity, OC and sediment distribution, and sediment OC lability have been generated within ArcGIS using fuzzy set theory. Our results show that the west coast of Scotland represents one of the key areas where sedimentary OC is potentially at greatest risk from bottom trawling activity. This is due mainly to the high reactivity of these OC rich sediments combined with the pressures of repetitive trawling activity within inshore waters. Our research shows that these OC hotspots are potentially at risk of disturbance from bottom trawling activity and should be prioritized for the consideration of future safeguarding (management) measures to ensure emissions are minimized and to provide greater protection of this natural carbon capital resource.
Article
This paper analyses the spatial distribution of fishing effort in a sample of 25 Dutch commercial beam trawlers fishing for sole and plaice in the period 1993–1996, based on an automated recording system with an accuracy of about 0.1 nautical mile. Intensive fishing occurred along the borders of the closed areas (12 mile zone and the “plaice-box”, a protected area in the eastern part of the North Sea) and at certain off-shore grounds in the southern and central North Sea. Effort distribution was studied within 30 × 30 (ICES rectangles), 10 × 10, 3 × 3 and 1 × 1 nautical mile squares and showed a patchy distribution. The degree of patchiness decreased with resolution. Within 3 × 3 mile squares, beam trawling was randomly distributed in some parts of the most heavily fished ICES rectangles but patchily distributed in others. Within 1 × 1 mile squares, the distribution became random within more than 90% of the squares. The micro-distribution showed a remarkable similarity between the 4 years with a mean coefficient of overlap of 0.66, range 0.56–0.76. The micro-distribution of the sampled vessels was raised to the total Dutch fleet in order to estimate the frequency at which the sea bed was trawled. It was estimated that during the four year study period in eight of the most heavily fished rectangles of the North Sea, 5% of the surface area was trawled less than once in 5 years and 29% less than once in a year. The surface area of the sea bed that was trawled between 1 and 2 times in a year was estimated at 30%. The surface area trawled more than five times in a year was estimated at 9%. The relevance of the findings for the study of the impact of beam trawling on the benthic fauna is discussed.
Article
Recreational clam digging is a traditional activity on the large intertidal zone of the western coasts of the Cotentin (western English Channel). A variety of fishing gears are used to harvest the target species the warty venus Venus verrucosa (Linnaeus, 1758). In this note, the immediate effect (i.e., four days) of fork harvesting was studied during the March 2012 spring tide, following a control-impact design with a control station and three impacted stations using pebble forks. An immediate significant decreases of coarse sand and gravel benthic macrofauna is observed in fishing area. In the future, it is recommended that pebble fork fishing should be prohibited to harvest this target species.
Article
Stomach contents of major commercial fish species in the Barents Sea (cod Gadus mohrua, had-dock Melanogrammus aeglefinus, and striped catfish Anarhichas minor) include the soft parts of large bivalvians—serripes Serripes gröenlandicus and Iceland scallop Chlamys islandica. The remains of serripes in the stomachs of fish are represented by muscular legs, while those of scallop by muscle and gonads. It is assumed that fish are likely to tear the soft parts of serripes during movement of a mollusk on the ground. Fish can consume the body of scallops only as scallop processing wastes or after shell crushing by fishing gear at bottom trawling and dredging.
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This study aimed to describe the characteristics of the by-catch of Cancer pagurus in king scallop dredges in the Isle of Man, and to determine the damage, immediate mortality and estimated mortality during fishing seasons associated with scallop dredges. Based on dredge surveys, spatial and seasonal variations were observed, with the highest number of crabs found off the west coast of the Isle of Man in the autumn when berried females crabs were most frequently caught. In general, female crabs comprised 84% of the catch. The damage levels of crabs was high with 45% of crabs recorded as crushed or dead or with severe damage, whilst 24% of crabs exhibited missing limbs. Estimates of the potential mortality associated with scallop dredging led to a lower and upper estimate of possible crab by-catch mortality of 15t and 24t respectively which represented 3.0–4.8% of the commercial landings of brown crab for the Isle of Man. Heaviest mortalities of crabs occurred in autumn to the west of the Isle of Man when female berried crabs move offshore into deeper water. The use of a temporary and spatially restricted scallop dredging closure could provide a simple solution to mitigate additional crab mortality in the event that scallop dredging increased beyond current levels in the future.
Article
Impacts of mobile fishing gears on habitat and benthos have been well-documented; in contrast, less studied physical impacts of static fishing gear on benthic habitats are still debated. Pot fishing, is a growing sector in the UK and evidence of any impacts is needed to inform management. This study simulated high intensity experimental pot fishing on the epibenthos of two common UK reef habitats in Northumberland, UK. Single tethered pots were fished in intensively and lightly fished areas over the course of 2 months. Within each area, three experimental sites and control sites were surveyed before and after fishing using photoquadrats (n = 240 per 290 m² site) collected by scuba divers. PERMANOVA analysis indicated no evidence of epibenthic species abundances decreasing due to physical crushing or abrasion from potting on either intensively or lightly fished reefs. A shift in community composition over time was detected but was attributed to natural change as epibenthos in control sites shifted similarly. Experimental pot impacts far exceeded those of the local commercial pot fishery, providing relevant evidence for statutory governing bodies revisiting current fisheries management. Results are applicable across Western Europe due to the selection of habitats with abundant and commonly distributed benthic species. © International Council for the Exploration of the Sea 2017. All rights reserved.
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Bottom trawling accounts for nearly a quarter of wild-capture seafood production, but it is associated with physical disturbance of the seabed leading to changes in benthic abundance, habitat structure, and biogeochemical processes. Understanding the processes of benthic depletion and recovery in relation to different types of fishing gears, and in different seabed types, is an important pre-requisite to inform appropriate management measures to limit or reduce the effects of trawling on the seabed. The combined approaches of meta-analysis and modelling that link fishing-gear penetration of the seabed to benthic depletion, and recovery to taxon longevity, have enabled the development of a modelling framework to estimate relative benthic status in areas subject to trawling. Such estimations are highly sensitive to the spatial resolution at which fishing footprint (trawl track) data are aggregated, and this leads to overinflated estimates of fishing impacts on benthos when coarse-level aggregation is applied. These approaches present a framework into which other “sustainability” criteria can be added, e.g., the consideration of carbon footprints of fishing activities.
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Small-scale fisheries contribute to food security and employ millions around the world. Overexploitation, however, threatens the suite of benefits that they can provide. Adopting innovations in gear technology can help to solve problems in fisheries (e.g. by-catch) but can also fuel overexploitation, with detrimental social, ecological, and economic impacts. Early assessments of the impacts of fishing gear innovations are crucial to preventing these innovations' adverse consequences. Using diverse methodologies, we assessed the impacts of a trammel net innovation in the cusk-eel small-scale fishery in central Chile. We show that the trammel net's adoption followed the path predicted by the diffusion of innovations theory and led to significant increases in landings. We also show, using a data-poor stock assessment methodology, that the red cusk-eel stock is overexploited. Next, we identified fishersperception of the ecological and economic impacts of the trammel net innovation. Finally, we used bidding games to assess fishers willingness to accept potential management measures to reduce the gear innovation impacts. Together, our results provide a comprehensive assessment of the trammel net innovation's diverse impacts in the cusk-eel small-scale fishery in central Chile and help identify potential ways forward. Timely and holistic assessments of the impacts of fishing gear innovations are essential to sustain fish stocks, promote responsible fishing and support the livelihoods of those who depend on fisheries worldwide.
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In Kiel Bay (Western Baltic), benthos samples were taken at 20 m water depth using rectangular botanical dredges fixed to the otter boards of an 80 ft Sonderborg standard trawl to document possible effects of trawl fishery on the benthic fauna. Thin-shelled bivalves like Syndosmya (Abra) alba, Mya spp. and Macoma calcarea, as well as the starfish Asterias rubens were damaged by otter-boards to a high extent. Thick-shelled bivalves such as Astarte borealis and Corbula gibba, however, seem to be more resistant to mechanical stress of bottom-trawl fishery. Musculus niger, an epibenthic species, is probably only resuspended and dislocated. The rate of damage to Arctica islandica, Macoma baltica and Macoma calcarea is related to their body size. Large specimens are more affected than smaller specimens due to the unfavourable relationship between shell surface and shell thickness. The size distribution of Arctica islandica in heavily trawled areas of Kiel Bay shows reductions in the upper size class in these areas.
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Tracks of bottom trawling gear, in particular of otter boards, have been mapped from side—scan sonar records. The extent of disturbance per unit area was quantified by relating the area covered by trawl to the total area. Frequency classes were defined and related to sediment type and water depth. The density of trawl tracks is highest below 20 m and in mud areas. Taking into account fishing effort data, it can be concluded that some areas are ploughed at least once a year by the boards alone.
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The diets of gurnards Aspitrigla cuculus and Eutrigla gurnardus, lesser-spotted dogfish Scyliorhinus canicula and whiting Merlangius merlangus were examined to determine whether they migrated into recently trawled areas to feed on animals that may be damaged or dislodged by the action of a 4 m beam trawl. Gurnards and whiting increased their intake of prey after an area had been fished. In particular, they increased the proportion of the amphipod Ampelisca spinipes in their diets. Beam trawling damaged the purple burrowing heart urchin Spatanguspurpureus, scallop Aequipecten operculans, Ensisspp. and Laevocardium sp., exposing internal tissues which were then eaten by whit- ing. Some mobile invertebrate scavengers, such as Pandalusspp., only occurred in diets after the area had been fished, suggesting that these animals were also scavenging over the trawl tracks. Observa- tions of the seabed using a side-scan sonar revealed a greater concentration of fish marks around the trawl tracks than in adjacent unfished areas. Our results indicate that fish rapidly migrate into beam trawled areas to feed on benthic animals whlch have been either damaged or disturbed by fishing or on scavenging invertebrates. In areas where certain benthic communities occur, beam trawling inten- sity may be such that it creates a significant food resource for opportunistic fish species. This is a possi- ble mechanism whereby long-term community structure could be altered by fishing activity.
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The passage of a beam trawl across the seabed leads to the direct mortality, or indirect mortality through subsequent predation, of some benthic species. In addition, animals retained in, or those that pass through, the cod end may also die as a result of the fishing process. The extent of this additional mortality needs to be quantified to calculate total mortality of non-target species associated with this type of fishery. Hence, we investigated the survival of animals caught by a 4 m beam trawl, in order to identify those species most sensitive to capture. Starfishes, hermit crabs and molluscs were highly resistent to the effects of capture (>60% survived in all cases). Fishes (except dogfish), sea urchins and swimming crabs suffered higher mortality after capture. Generally, the majority of the animals that passed through the meshes of the cod end survived. Experimental investigation of the cause of damage to certain species concluded that the chain matrix fitted to the gear was largely responsible for the injuries sustained. The types of injuries and their extent were species-specific, and were related to the fragility and physical characteristics of each species. Our experiments revealed that while some species are highly sensitive to capture, others are capable of surviving the effects of capture.
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1Some effects of fisheries on the associated biological systems are reviewed and management options and their inherent risks are considered.2In addition to the effects on target species, other sensitive groups impacted by fishing are considered including marine mammals, turtles, sea birds, elasmobranchs and some invertebrates with low reproductive rates.3Other impacts discussed include the destruction of benthic habitat, the provision of unnatural sources of food and the generation of debris.4Management options are considered including the designation of marine protected areas, risk aversion, and the burden of proof.5A balanced consideration of the risks and consequences of ‚Type 1’ and ‚Type II’ errors is advocated.
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1. Beam-trawling is a source of physical disturbance to marine sedimentary communities in areas less than 50m deep, on the western European continental shelf. Chains attached between the beam-trawl shoes are designed to penetrate the upper few cm of the sediment, which leads to the damage or removal of some infaunal and epifaunal species. In some areas, beam-trawling may be frequent and intense, leading to speculation that it may generate long-term changes in the local benthic fauna. 2. As part of a larger MAFF study examining the ecological effects of beam-trawling, we investigated its local impact on an infaunal community in the north-eastern Irish Sea. Studies of this type are complicated by the heterogeneity of the environment, hence we adopted a replicated, paired control and treatment design to maximize the chances of detecting any effects due to trawling. 3. A side-scan sonar survey revealed that the experimental area was characterized by mobile megaripples in the south-eastern sector of the experimental area and stable sediments with uniform topography in the north-western sector. Multivariate analysis of the species abundances from the control areas separated the fauna into two distinct communities which corresponded to the different substratum characteristics. Data from the two regions were therefore treated separately when testing for the effects of trawling. 4. In the north-western sector, trawling led to 58% decrease in the mean abundance of some taxa and a 50% reduction in the mean number of species per sample. Multivariate analysis revealed that differences between control and fished sites were largely due to the reduction or removal of less common species. These effects were less apparent in the mobile sediments of the south-eastern sector, which had a naturally impoverished fauna and high level of heterogeneity. 5. Univariate variables, such as abundance and the total number of species per sample, indicated that the variation between replicate samples increased as a result of trawling disturbance. However, examination of the community data using an index of multivariate dispersion revealed no difference between fished and unfished areas. This suggests that the effects of fishing disturbance are consistent between replicate samples. 6. Fishing with demersal gears modifies communities in relatively stable sediments. Frequent and repeated physical disturbance by fishing gears may lead to long-term changes in the benthic community structure of these habitats.
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Fishers have been complaining about the effects of bottom trawl gear on the marine environment since at least the 14th century. Trawl gear affects the environment in both direct and indirect ways. Direct effects include scraping and ploughing of the substrate, sediment resuspension, destruction of benthos, and dumping of processing waste. Indirect effects include post‐fishing mortality and long‐term trawl‐induced changes to the benthos. There are few conclusive studies linking trawling to observed environmental changes since it is difficult to isolate the cause. However, permanent faunal changes brought about by trawling have been recorded. Research has established that the degree of environmental perturbation from bottom trawling activities is related to the weight of the gear on the seabed, the towing speed, the nature of the bottom sediments, and the strength of the tides and currents. The greater the frequency of gear impact on an area, the greater the likelihood of permanent change. In deeper water where the fauna is less adapted to changes in sediment regimes and disturbance from storm events, the effects of gear take longer to disappear. Studies indicate that in deep water (>1000 m), the recovery time is probably measured in decades.
Article
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As part of an investigation into the impact of commercial trawling on the benthos of Strangford Lough a map of the distribution of the benthic communities in the Lough was required. To provide this an acoustic bottom classification survey of the Lough was carried out using a commercially available system, RoxAnn. RoxAnn processes the information from a conventional echo-sounder to determine the nature of different substrata. Underwater cameras were used to obtain ground truth data to compare with the RoxAnn data. Used in conjunction, the two surveys provided valuable information on the different bottom substrata and associated epibenthic communities present in the Lough.
Article
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Surveys of the benthic invertebrates of the southern Irish Sea were carried out in 1989 and 1991. Both quantitative (grab) and qualitative (trawl and dredge) samples were taken for faunal and sediment analysis. The fauna is very rich with some 1030 species recorded. Polychaete worms dominate the fauna followed by the Crustacea and Mollusca. The fauna is not only diverse but is also very abundant, reaching 17,348 individuals per square metre. Many taxonomic problems were encountered, indicating that there remains much basic work to be undertaken. Over twenty polychaete species are possibly new to science and a new species of solenogastre mollusc has already been described. In addition there are many records of species new to British waters as well as to the Irish Sea. The southern Irish Sea can be said to be part of the “Boreal” zoogeographic province but there are also more southern “Lusitanian” influences in the area of the Celtic Deep. Three major faunal assemblages are defined which coincide with general sediment distributions relative to depth. ''Assemblage A" occurred in the deeper mud and sandy mud regions of the Celtic Deep; "Assemblage B" was found in the inshore sandy and muddy sand areas, and "Assemblage C" coincided with the offshore gravelly sediments. The traditional view of fixed communities is not supported here, rather there occurs a mosaic of looser assemblages overlapping in their responses to changing environmental conditions. Species diversity was measured and showed that the gravelly sediments supporting "Assemblage C" were the richest with an average of 145 taxa per station. Diversity indices were calculated and a Shannon- Wiener value of 6.34 is the highest yet recorded from British waters. The high species richness values from the southern Irish Sea compare well with those reported from the very diverse deep-sea benthos. The southern Irish Sea can be regarded as a significant pool of marine biodiversity warranting care and further investigation.
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In the early 1980s, a strategy for graphical representation of multivariate (multi-species) abundance data was introduced into marine ecology by, among others, Field, et al. (1982). A decade on, it is instructive to: (i) identify which elements of this often-quoted strategy have proved most useful in practical assessment of community change resulting from pollution impact; and (ii) ask to what extent evolution of techniques in the intervening years has added self-consistency and comprehensiveness to the approach. The pivotal concept has proved to be that of a biologically-relevant definition of similarity of two samples, and its utilization mainly in simple rank form, for example ‘sample A is more similar to sample B than it is to sample C’. Statistical assumptions about the data are thus minimized and the resulting non-parametric techniques will be of very general applicability. From such a starting point, a unified framework needs to encompass: (i) the display of community patterns through clustering and ordination of samples; (ii) identification of species principally responsible for determining sample groupings; (iii) statistical tests for differences in space and time (multivariate analogues of analysis of variance, based on rank similarities); and (iv) the linking of community differences to patterns in the physical and chemical environment (the latter also dictated by rank similarities between samples). Techniques are described that bring such a framework into place, and areas in which problems remain are identified. Accumulated practical experience with these methods is discussed, in particular applications to marine benthos, and it is concluded that they have much to offer practitioners of environmental impact studies on communities.
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The great scallop Pecten maximus has been actively fished for >50 yr around the Isle of Man. Since 1969 there has also been a large fishery for queen scallop Aequipecten opercularis. Scallop dredging employs gear which also removes other non-target species (by-catch). By-catch composition varied between grounds. Some species appeared to be more susceptible than others to dredge damage with no mortality occurring amongst the more robust species. Large numbers of the more easily damaged species may be killed each year, however.
Article
1. The effects of physical disturbance processes on marine benthic communities remain an issue of considerable theoretical and practical importance, particularly with respect to the impact of fisheries activity and possible conflict with wildlife conservation objectives. One area where particular concern has been raised is with respect to the effects of mechanical harvesting of cockles (Cerastoderma edule) on non-target benthic infauna in intertidal communities. 2. This paper describes the results of manipulative field experiments which examine the effects of disturbance by two mechanical cockle harvesting methods, hydraulic suction dredging and tractor dredging. 3. Although the suction dredge experiment revealed some statistically significant effects, taken as a whole the results indicated that the faunal structure in disturbed plots recovered (i.e. approached that of the un-disturbed controls) by 56 days. This occurred against a background of consistent increases in the abundance of many taxa in both treatments, which we interpret as the normal seasonal response of the community. 4. The tractor dredge experiment revealed fewer statistically significant effects than the suction dredge experiment, and recovery from disturbance occurred against a background of general seasonal decline in the abundance of the fauna. From the available evidence the most likely mechanism of recovery was through the immigration of adults into disturbed areas. 5. We conclude that mechanical harvesting methods impose high levels of mortality on nontarget benthic fauna, but that recovery of disturbed sites is rapid and the overall effects on populations is probably low. Although our results suggest that tractor dredging has less effect than suction dredging, this result is most likely to be a consequence of the different times of year in which the experiments were conducted. Thus, for this location, we do not believe that a distinction can be made between the effects of the two methods. Although experimental manipulations cannot be conducted on comparable spatial scales to real fishing activity, we believe these results probably do not represent a major under-estimate of recovery times for intertidal habitats similar to the one chosen for this study.
Article
An attempt is undertaken to analyse the ground-rope effect on the efficiency of beam trawls in assessing population densities of epibenthic animals, such as demersal fishes, shrimps, crabs, asteroids, ophiuroids, and gastropods, which burrow to a greater or lesser degree. Experimental beam-trawl hauls were carried out with different numbers of tickler chains. The results obtained in sandy as well as in muddy areas are discussed. In general, no significant effect of the number of tickler chains was found at muddy stations. At sandy stations, on the other hand, the number of tickler chains showed a positive effect on the catches of species that burrow occasionally and species that cling tightly to the bottom. In some species the catches reached an asymptotic level with increasing number of chains, whereas in other cases the increase in the catches was still significant even when reaching the maximum of 6 chains.
Article
Tracks of three types of fishing gear in bottom sediments were observed from a submersible in Chaleur Bay (Gulf of St. Lawrence). Tracks left by past otter trawling activities covered at least 3% of the bottom by area and were considered to have been made by trawl doors.Shallow tracks made by inshore and offshore scallop dredges during the course of the study could be distinguished from each other and from trawl tracks.Scallop dredging lifts fine sediments into suspension, buries gravel below the sand surface, and overturns large rocks embedded in the sediment, appreciably roughening the bottom. The inshore Alberton dredge is inefficient, dumping its contents back onto bottom at intervals during the tow.Dredging causes appreciable lethal and sublethal damage to scallops left in the track, this damage being greatest on rough bottom. Incidental mortalities to scallops with an offshore dredge of at least 13–17% per tow are of the same order of magnitude as estimates of harvesting efficiency made in earlier studies.Predatory fish and crabs were attracted to the dredge tracks within 1 hr of fishing and were observed in the tracks at densities 3–30 times those observed outside the tracks.
Article
1. Preliminary estimates of the relative sensitivity of sea bed types and benthic species to physical disturbance, particularly fishing activity, have been made in order to identify areas where further studies are required and to help formulate management plans for sites of marine conservation importance. 2. Physical disturbance is considered in the context of a single encounter with fishing gear followed by a recovery period during which there is no fishing, but with a view to qualifying, in the future, the effect of multiple fishing events. Disturbance is considered in terms of the physical action of the gear on the sea bed and the unit area over which this action occurs. 3. The effects of a wide range of gears are considered. Static gears, which can be employed on a variety of substrata, generally result in low level impacts for single fishing events and impacts are localized compared with the effects of mobile gears, which can extend over considerable areas. 4. The theoretical sensitivity of individual species is assessed on the basis of how well they cope with an encounter with fishing gear and on their likely recovery from destruction in terms of their reproductive strategies. 5. Species considered of key importance in the structuring of communities are suggested and examples of particularly sensitive species, which are therefore likely indicator species of physical disturbance, are listed. 6. Fragile, slow recruiting animals are considered to be most susceptible to disturbance, while the least sensitive species are generally fast growing and have good recruitment.
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The mesozooplankton taken in continuous plankton recorder samples from the Central North Sea has changed from being numerically dominated by holoplanktonic calanoid copepod species from 1958 to the late 1970s to a situation where pluteus larvae of echinoid and ophiuroid echinoderms have been more abundant than any single holoplanktonic species in the 1980s and early 1990s. The abundance of the echinoderm larvae as a proportion of the zooplankton taken in the samples has followed a continuous increasing trend over the Dogger Bank, but off the eastern coast of northern England and southern Scotland the increase did not become obvious until the 1980s. This trend is consistent with reported increases in abundance of the macrobenthos. It is proposed that changes in the benthos have influenced the composition of the plankton.
Article
The presence of certain species of benthic infauna in catches from a beamtrawl indicated that tickler chains and the ground chain can scrape off successive layers of sediment and reach at least 6 cm into the sediment. Direct effects of beamtrawling on benthic species in the North Sea were determined by comparing faunal abundance before and after commercial beamtrawling on a hard-sandy sediment. In autumn 1989 three-fold trawling of the experimental area resulted in a decrease in density (10–65%) of a number of species of echinoderms, polychaetes and molluscs.
Article
A preliminary survey of benthic infauna from an extensive basin of soft mud in the Irish Sea was carried out in 1992. A total of 110 taxa were recorded of which polychaete worms (Phylum Annelida) constituted 77·8% of all taxa recorded. Hierarchical classification and detrended correspondence analysis divided the area studied into five regions which could be correlated to the differences in superficial sediments and depth across the basin. Although much of the fauna was ubiquitous, a change in trophic structure was observed, with tubiculous polychaetes becoming progressively less common in deeper softer sediment areas where surface and non-selective deposit-feeding taxa predominated.
Article
This review follows the style of two earlier reviews of the inshore fisheries of England and Wales but certain sections have been expanded (e.g. management framework and descriptions of fishing gear) . The bulk of the report summarises the coastal fisheries by 11 regions. There is a general overview of each fishery sector (demersal, pelagic, shellfish, migratory species) within each region and then a resume of the activity undertaken from each port or landing place within the region. -from Author
Article
Populations of sole and plaice were sampled on and around a nursery on the North Wales coast during May, July and October 1989 and 1990, and the distribution of age-groups described. Pre-recruit sole were tagged and released on the same area during September 1988 to provide information on their larger scale movements. Juvenile sole remained on the nursery ground close inshore until after their first winter, whereas plaice of the same age-group became more widely dispersed. Both species were still associated with the coastal zone as 2-groups, when they were vulnerable to capture by commercial trawls. The gradual movement of sole out of the nursery was almost complete by October of their third year. Sole tag returns were obtained mainly from the NE Irish Sea, and also from the E coast of Ireland. Only three of the 68 returns came from outside the Irish Sea, one from the SE Irish coast, one from Swansea Bay and another from the outer Bristol Channel. Published data indicated that plaice undergo more rapid and more extensive migrations within and away from the Irish Sea than sole of the same age-group. Juvenile plaice and sole populations from nursery grounds throughout the NE Irish Sea would become mixed, and could contribute to any of the spawning populations in that area.
Chapter
This review examines the physical and biological processes which move marine intertidal and subtidal sediments and considers available information on the consequences of physical disturbance for benthic communities. The agents examined include waves and currents, bioturbation, fishing and dredging and the intensities and scales upon which the various processes operate is considered. The inter-relationships between the various disturbance processes are also examined.
Article
Unusually high densities of juvenile flatfish in some areas of a nursery ground, and complete absences from other areas, were associated with a dense bloom of the colonial alga Phaeocystis pouchetii along the coast of North Wales. A possible explanation for these movements, and for the presence of patches of anoxic sediments, is proposed.
Article
Populations of sole and plaice were sampled on and around a nursery on the North Wales coast during May, July arid October 1989 and 1990, and the distribution of age-groups described. Pre-recruit sole were tagged and reieased on the same area during September 1988 to provide information on their larger scale movements. Juvenile sole remained on the nursery ground close inshore until after their first winter, whereas plaice of the same age—group became more widely dispersed. Both species were still associated with the coastal zone as 2-groups, when they were vulnerable to capture by commercial trawls. The gradual movement of sole out of the nursery was almost complete by October of their third year. Sole tag returns were obtained mainly from the NE Irish Sea. and also from the E coast of Ireland. Only three of the 68 returns came from outside the Irish Sea, one from the SE Irish coast, one from Swansea Bay and another from the outer Bristol Channel. Published data indicated that plaice undergo more rapid and more extensive migrations within and away from the Irish Sea than sole of the same age-group. Juvenile plaice and sole populations from nursery grounds throughout the NE Irish Sea would become mixed, and could contribute to any of the spawning populations in that area.
Article
An experimental dredging operation was carried out in a small sandy bay in Scotland, with the aim of quantitatively assessing the effects of scallop dredging on the benthic fauna and the physical environment. An area within the 10-m depth contour was selected; a 1.2-m modified scallop dredge was operated at frequencies of 2, 4, 12 and 25 dredges, carried out over a period of nine days. The effects on the bottom topography, the physical characteristics of the sediment and the fauna were investigated by grab and core sampling, and direct observations were carried out by a diving team.Observed changes in bottom topography were not translated into changes in the disposition of the sediments, their grade distribution and the organic carbon and chlorophyll content, all of which showed no effects.The infaunal community, which consisted of bivalve molluscs and peracarid crustaceans, both taxa adapted morphologically and behaviourally to a dynamic environment, did not show any significant changes in abundance or biomass. Sessile forms such as polychaetes showed a noticeable decrease, and the burrowing spatangid Echinocardium was substantially reduced from the dredged area. Corresponding changes in the biomass of the different taxa were also evident but not significant.However, the most important effect of this experiment was on the epifaunal and large infaunal organisms recorded by the divers. Large numbers of molluscs (Ensis), echinoderms (Asterias) and crustaceans (Cancer) were killed or damaged by the dredging operations. Very large concentrations of the burrowing sand eel Ammodytes were also destroyed. The overall conclusion to be drawn from this experimental dredging operation is that its effect was limited tot he selective elimination of a fraction of the fragile and sedentary components of the infauna, and the destruction of the large epifaunal and infaunal organisms.
Article
The Irish Sea ia a relatively small, enclosed sea area which is subject to a wide range of human uses including navigation, oil terminals, dumping of sewage and industrial sludge, cooling for nuclear power stations, gravel extraction, gas and oil prospecting and fishing. Commercial fishing is affected by the other uses and at the same time it provides a means of monitoring their effects on a part of the ecosystem. Regular samples taken from fish markets provide a long series of age-composition data of the main commercial species — cod, whiting, plaice and sole — from which population changes can be assessed. More recently groundfish trawl surveys have been carried out to provide more detailed information on the distribution of all demersal fish species seasonally and in relation to area, depth and sediment type. Advice on the management of commercial fish species is prepared by a working group of the International Council for the Exploration of the Sea (ICES), and is based mainly on analytical single-species models. There are obvious shortcomings of such models in an area of mixed fishery and high diversity such as the Irish Sea. The objectives adopted in these models and in fisheries management generally are examined critically in relation to the possible aims of conservation.
Article
Numerous field observations have revealed that turbulence created in the wake of trawl doors can generate large and highly turbid clouds of suspended sediment. Time-averaged concentrations of sediment resuspended by trawls from various areas of the Middle Atlantic Bight continental shelf have been estimated using a simple mathematical model and National Marine Fisheries Service records of commercial trawling activity. Mean concentrations of sediment put into suspension by currents have also been computed using a modified form of the Glenn and Grant model. The results indicate that sediment resuspension by trawling can be a primary source of suspended sediment over the outer shelf, where storm-related bottom stresses are generally weak. The concentration estimates further suggest that sediment resuspended by trawls makes a sizeable contribution to the total suspended sediment load over the heavily trawled central shelf area of Nantucket Shoals during all times except winter and early spring. The level of trawling activity declines dramatically going seaward across the outer shelf. This decline coupled with cross-shore water motions in the area appears to result in a net offshore transport of sediment across the shelf edge. However, the estimated magnitude of this transport indicates that trawling does not produce significant short-term erosion of outer shelf sediments.
Article
This paper presents an overview of current knowledge on the effects of trawling, dredging and ocean dumping on the eastern Canadian continental shelf seabed. The impact of trawling and dredging for fish and shellfish on marine habitats has recently attracted international attention among fisheries and environmental scientists. In Atlantic Canada, trawling and dredging are the principal methods of harvesting groundfish and scallops and ocean clams, respectively. It is estimated that fish trawlers and scallop dredges have swept tracks, cris-crossing the Canadian continental shelf, approximately 4.3 million km in length in 1985. In the past few years several studies were carried out by scientists from Canada, the United States and Europe to assess the impacts of trawling and dredging but results were inconclusive. Some studies showed physical damage as well as biological effects, whereas others indicated that the adverse effects were not considered to be serious.
The Potential ,fbr Cultivation and Rmtocking of' Pecten masinius
  • U A W Wilson
Wilson, U. A. W. 1994. The Potential,fbr Cultivation and Rmtocking of' Pecten masinius ( L. ) and Aequipecten operculuris ( L. ) on A4un.u Inshore Fishing G r o ~ i n d ~, PhD thesis, University of Liverpool, 198 pp.
Some observations on the penetration into the sea bed of tickler chains on a beam trawl', International Council for the Exploration of the Sea C MImpacts of flounder trawls on the intertidal habitat and community of the Minas Basin, Bay of Fundy
  • J P Bridger
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Bridger, J. P. 1972. 'Some observations on the penetration into the sea bed of tickler chains on a beam trawl', International Council for the Exploration of the Sea C M 1912/B: 7, 9pp. Brylinsky, M., Gibson, J. and Gordon, D. C. Jr. 1994. 'Impacts of flounder trawls on the intertidal habitat and community of the Minas Basin, Bay of Fundy', Canadian Journal of Fisheries and Aquatic Science, 51, 650-661.
North Irish Sea scallop fisheries: a review of changes An International Compendium of Scallop Biology and Culture. World Aquaculture Society
  • A R Brand
  • E H Allison
  • E J Murphy
Brand, A. R., Allison, E. H. and Murphy, E. J. 1991. 'North Irish Sea scallop fisheries: a review of changes, in Shumway, S. E. and Sandifer, P. A. (Eds), An International Compendium of Scallop Biology and Culture. World Aquaculture Society. Baton Rouge, USA. pp. 204-218.
The effect of commercial trawling on sediment resuspension and transport over the middle Clarke on-parametric multivariate analyses of changes in community structure
  • J H K R Churchill
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Churchill, J. H. 1989. 'The effect of commercial trawling on sediment resuspension and transport over the middle Clarke, K. R. 1993. " on-parametric multivariate analyses of changes in community structure', Australian Journal of Clarke, K. R. and Warwick, R. M. 1995. Change in Marine Communities: An Approach to Statistical Analysis and Interpretation, Natural Environmental Research Council, UK, 144 pp.
The Coastal Fisheries qf England and Wales, Part II, Review of their Status in 1988. MAFF internal report, No. 19The effects of storms on the dynamics of shallow water benthic associations
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Pawson, M. G. and Rogers, S. 1. 1989. The Coastal Fisheries qf England and Wales, Part II, Review of their Status in 1988. MAFF internal report, No. 19. Rees, E. I. S., Nicholaidou, A. and Laskaridou, P. 1977. 'The effects of storms on the dynamics of shallow water benthic associations', in Keegan B. F., Ceidigh, P. 0. and Boaden, P. J. S. (Eds), Biology of Benthic Organisms.
Micro distribution of beam-trawl effort in the southern North Sea
  • A D Rijnsdorp
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Rijnsdorp, A. D., Groot, P. and Beek, F. A. van. 1991. 'Micro distribution of beam-trawl effort in the southern North Sea', Internutionul Counci1,fiir the E,~ploratioti of the Seu, CM 1991/G: 49, 20 pp.