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1.
Sea trials and application of a numerical method for the analysis of the ocean current displacement phenomena of demersal longlines 总被引：2，自引：0，他引：2
In this study, a numerical method for the analysis of the sinking speed of demersal longlines was developed to obtain further insight into the ocean current displacement of demersal longlines. The sinking speed is one of the main factors affecting the extent of current displacement, which is the horizontal movement of longlines due to ocean currents.To improve the accuracy of the model, bait properties were investigated in a flume tank, and the resistance coefficients of full scale models based on different bait shapes, sizes and orientations were established. The numerical method was verified by full scale experiments conducted in the sea.In the theoretical analysis, the sinking speed of a Norwegian commercial longline was calculated. Current-related data of a common longlining area in Norway were obtained from the Acoustic Doppler Current Profiler (ADCP) and were used to calculate the ocean current displacement of a demersal longline. The results show the ocean current displacement of longlines, and make to expect a decrease in the fishing efficiency. 相似文献
2.
《Marine Policy》2016
In the Northeast Atlantic, elasmobranchs are a common bycatch in many fisheries, including demersal trawls, longlines, or gillnets and many countries do not have regulations or any control over the amount taken. In the Mid Atlantic, the Azores EEZ (Exclusive Economic Zone), small-scale fishing operations, artisanal and hook-and-line fishing methods are responsible for part of local total landed elasmobranch biomass, although some species are specifically focused and severely harvested by international large-scale fleets. This work provides a review and analysis of the commercial elasmobranch fisheries in the Azores EEZ, and its evolution over the last two decades, highlighting management priorities, taking into account the Northeast Atlantic elasmobranch fisheries status. In the Mid-Atlantic, elasmobranch fisheries mainly target 4 species, that are usually landed as bycatch: the tope shark (Galeorhinus galeus) and the thornback ray (Raja clavata), captured mainly by local demersal artisanal fisheries, the blue shark (Prionace glauca) and the shortfin mako shark (Isurus oxyrinchus) captured by a more industrialised fleet, including those from foreign nations. Considering elasmobranchs life history traits and fishery history, caution is advised in the development of a management strategy focusing on these species, considering the Northeast Atlantic context and regional, local and national interests. 相似文献
3.
The East Sea, with an average depth of 1700 m, has long been subject to heavy fishing pressure, resulting in derelict fishing gear. Most derelict fishing gears, such as fishing nets, fishing ropes, and crab pots, sink to the seabed and do not degrade. This gear results in “ghost fishing,” which has adverse impacts on deep benthic habitats. Recently, the Korean government has started to remove derelict fishing gears from the deep seabed of the East Sea by bottom trawling with heavy hooks (50–80 kg) and ropes. A total of 207.8 and 252.2 tons of marine debris in 2009 and 2010, respectively, were removed from the seabed, most of which were derelict fishing gears. Contrary to monitoring surveys and clean-up in shallow waters, removal of marine debris from remote deep habitats is much more difficult and dangerous for removal crews. 相似文献
4.
《Marine Policy》2014
Fisheries management determines how much of each stock can be landed when, where and how fishing is permitted. It has been identified to strongly influence the environmental performance of the fishing industry, including fuel use. As fuel data for fisheries is scarce, especially on a detailed level, the aim of this study was to develop an approach for utilizing fleet-wide fuel data to estimate the fuel use of individual fisheries and mapping how fuel efficiency in Swedish fisheries is influenced by management. Swedish demersal trawl fisheries were studied between 2002 and 2010. Results show that the overall fuel efficiency has improved and interesting patterns between different fisheries and vessel sizes emerged. The difference in fuel efficiency per kilo landing between large and small trawlers was generally small, unless catch capacity was lowered e.g. by selective grids. Stock rebuilding was shown to be highly important for fuel efficiency, as fuel use was inversely correlated to the biomass of eastern Baltic cod. However, rebuilding can also lead to trade-offs e.g. in the case of selective trawling, where protection of depleted stocks comes at the cost of higher fuel intensity per landing. Finally, tax exemption of fuel use in fisheries was shown to maintain inefficient fisheries. These results could be used to reduce overall environmental impacts of fishing further by incorporating fuel use as an additional aspect into the fisheries management system. 相似文献
5.
《Marine Policy》2014
Interactions between seals and the fishing industry are an on-going problem in Ireland and indeed globally across the range of most seal species. These interactions occur at both the operational (seal damage to catches and fishing gear) and biological (competition for shared resources) level. With declines in fish stocks there has been increased interest in the extent of competition for resources between commercial fisheries and seals. High levels of seal damage perceived by the fishing industry has led to frequent calls for seal culls, highlighting the significance of the problem. However, the scale of interaction between seals and commercial fishing and aquaculture in Ireland heretofore remained unclear. A comprehensive review of existing data, augmented with data from key stakeholders on the current state of play is presented to provide a realistic and representative account of the situation. This suggests that seal interactions with commercial fisheries in Ireland are most significant in inshore (<12 nautical miles from shore) static-net (or passive) fisheries (e.g. gill/tangle nets) and have increased following the driftnet ban in 2006, which suggests displacement of seal interactions from salmon to other fisheries. The industry highlighted pollack, angler fish, cod, and turbot fisheries as the main inshore fisheries currently impacted by operational damage to gear and catch by seals. Seal damage to line-caught salmon continues, with industry feedback suggesting large geographical variation in the range of damage levels reported. Salmon farming installations are also increasingly being targeted by seals, with significant losses due to seal depredation being reported. In the absence of robust data on seal depredation, the extent to which changes in fishing gear and practices have reduced damage levels, or resulted in displacement of seal foraging effort, is unknown. Recommendations are made to suggest how research efforts should be focused to address critical data gaps identified in the study. 相似文献
6.
《African Journal of Marine Science》2013,35(1):773-789
There are two types of interactions between seals and commercial fisheries in South Africa: biological (potential competition for shared resources between the two "predators") and operational (conflicts during fishing operations). Using data for the 1980s, a comparison is made of relative consumption by different predators in South African waters. Seals and fisheries are not the major consumers in the system, but they do take comparable amounts. This has resulted in calls for a reduction in the seal population, but to date, no studies have shown that reducing seal predation of commercial species will make more fish available for the fisheries. Most fisheries are subject to some form of operational interaction with seals. These interactions include consumption of catches (operational consumption), disturbance of fishing operations (operational disturbance) and damage to fishing gear (operational gear damage); they vary in degree of severity, both seasonally and regionally. Estimates of the consumption by seals from fishing operations in South Africa show it to be a minimal percentage of fishery catches and a small proportion of the total predation by seals. Preliminary calculations of overall economic losses resulting from seal interference show this to be small in comparison with the wholesale value of the catches. Seals die as a result of fishing operations, and estimates of the potential mortality through entanglement, drowning and deliberate killing indicate this mortality to be of a magnitude that should be monitored. 相似文献
7.
Bycatch reduction technologies (BRTs) have been developed to limit the incidental capture of non-target marine species in fishing gear, especially those species of special concern. However, in the absence of enforcement, the proven effectiveness of a BRT alone does not guarantee its adoption by fishermen. Human factors also play a fundamental role. This case study was directed at evaluating the willingness of Sicilian longline fishermen to use relatively large circle hooks (size 16/0) as a BRT for the loggerhead sea turtle Caretta caretta. Fishermen were involved in testing circle hooks with their fishing vessels and their own commercial fishing gear, and their opinions before and after trials at sea were recorded. The present study showed the importance of creating a positive human context for testing a BRT. Findings provided additional confirmation about the usefulness of relatively large circle hooks to reduce the bycatch of loggerhead sea turtles on drifting longlines. Interviews before and after trials at sea indicated that socio-economic and emotional factors are essential for successful uptake of BRTs. Crews of large fishing vessels stated that they would be willing to use circle hooks in months with a high probability of turtle captures (June-September) if an economic incentive was provided and there was also public acknowledgement of their efforts. The fishermen's cooperatives association involved in the project is currently evaluating the creation of a product label identifying the harbors where fishing was performed using circle hooks. 相似文献
8.
《Marine Policy》2013
Whale depredation occurs when whales steal fish, damage fish or damage fishing gear. In Alaska, killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) primarily depredate on demersal sablefish (Anoplopoma fimbria) and Pacific halibut (Hippoglossus stenolepis) longline fisheries. Quantitative data on whale depredation in Alaska is limited due to low fishery observer coverage and minimal depredation evidence left on longline fishing gear. This study utilized semidirected interviews (n=70) and written questionnaires (n=95) with longline fishermen to examine: (1) perceptions and experiences of whale–fishery interactions in Alaska, (2) effects of depredation on fishing practices, and (3) potential depredation mitigation measures. Eighty-seven percent of fishermen surveyed agreed that whale depredation became worse between 1990 and 2010. Respondents reported changing their fishing practices in response to depredating whales in several ways, including: traveling up to 50 nautical miles and ceasing hauling operations up to 24 h until the whales left the fishing grounds. Respondents fishing in western Alaska, primarily encountering killer whales, were forced to wait longer and travel greater distances than fishermen operating in central and southeast Alaska, regions more affected by sperm whales. Deterrent research, gear modifications and real-time tracking of depredating whales were solutions favored by study participants. Survey respondent answers varied based on areas fished, quota owned, years involved in the fishery and vessel size. This study presents the first statewide evaluation of fishermen's perception and knowledge of whale interactions with the Alaskan longline fleet and is a critical step toward developing baseline data and feasible depredation mitigation strategies. 相似文献
9.
Quantitative measurement of the response of benthic habitats to impact from towed fishing gears is of great importance to the ecosystem and the long-term management of sustainable fisheries. To date, most studies on the effects of trawling on the benthos have focussed on before/after, control/impact comparative studies. This research has proved important in terms of describing general trends and has identified taxa that suffer high levels of mortality, and habitat types where impact is the greatest. A limitation, however, to this comparative work is the lack of prediction-based methodology and it would be very beneficial to develop a more mechanistic approach that would allow trawling impact on the benthos to be estimated for a wider range of species and habitats. This paper is a first step in this approach and focuses on modelling the physical interaction between gear components and the seabed. In particular the penetration and disturbance to the seabed caused by (i) the roller clump of a twin trawl and (ii) a trawl door, are examined.A finite element (FE) model of the interaction of these components and the seabed is developed using the different soil models and features available within the Abaqus finite element software package. The resulting models are able to predict the penetration depth and sediment displacement associated with each gear component and the predictions are compared with the results obtained during sea trials. The sea trials were undertaken on two sediment types at depths accessible to scientific divers using SCUBA diving techniques who measured and profiled the physical alteration to the seabed following the passage of a roller clump and a trawl door. In addition, drag forces obtained from the sea trials are compared with numerical predictions of the drag related to the soil and the estimated fluid drag. Good agreement between the experimental trials and numerical simulations is found and hence this study provides the basis for investigation of the interaction of other components and sediment types. 相似文献
10.
《Marine Policy》2015
California sea lions (Zalophus californianus) off the coast of Southern California are known to damage both commercial and recreational fishing activities, causing decreases to fish catch and damage to gear. Their increasing population has intensified the potential for conflict between sea lions and anglers, likely requiring changes to current legislation. The recreational fishing community in Southern California is a valuable and largely underutilized source for information and potential solutions to management and legislative problems. This recreational fishing survey-based study conducted in 2013 utilized personal interviews, conducted in the field with recreational anglers and commercial passenger fishing vessel (CPFV) crews in Southern California, to gather data on: (a) the occurrence and impact of sea lion depredation on the local fishing, (b) angler awareness and opinions on current legislation, and (c) the conflict between fishing activities and conservation efforts. Results show that surveyed CPFV operators and private boaters had the most conflict with sea lions and perceive them as more of a problem than anglers on piers, jetties or kayaks. The conflict was also reportedly more prevalent in San Diego County compared to the other counties surveyed (Orange, Los Angeles and Ventura). Participating CPFV operators were overwhelmingly in support of a government culling program for sea lions, while recreational angler respondents did not feel that a control program was necessary. These CPFV operators reported more money lost, and were willing to pay more for an effective deterrent device. There was also a consensus among respondents that fish catch is declining, yet anglers were unsatisfied with the effectiveness of current legislation designed to increase fish stocks. These data will provide a better understanding of California sea lion depredation in Southern California and its effect on recreational anglers in order to aid future mitigation efforts. Additionally, these results provide stakeholder feedback on local marine protected areas and other fisheries management legislation, and build a foundation for future conservation and education programs. 相似文献
11.
Randall ReevesCheryl Rosa J.Craig GeorgeGay Sheffield Michael Moore 《Marine Policy》2012,36(2):454-462
The objective of this paper was to investigate and illustrate how insights gained from experience managing human activities in order to protect North Atlantic right whales (Eubalaena glacialis) along the heavily industrialized east coast of North America might be applied in the Arctic, where bowhead whales (Balaena mysticetus) face some of the same risks as right whales. The reduced extent and thickness of sea ice and the resultant longer open-water season have major, complex implications for the Arctic marine ecosystem. Increased maritime ship traffic and commercial fishing in the Arctic are bound to affect bowheads and Native (indigenous) hunting communities who depend on whales for subsistence and cultural identity. Bowheads and right whales were greatly depleted by commercial whaling in the 19th and early 20th centuries. While the Western Arctic bowhead population has been recovering steadily in recent decades, North Atlantic right whales remain highly endangered because of persistent lethal and sublethal vessel strikes and frequent entanglement in commercial fishing gear. Entanglement can be transitory or persistent, with debilitation lasting for months before the animal finally succumbs. Vessel strike and fishing gear trauma has been documented in bowheads, but at a much lower rate than in right whales. Initiatives intended to mitigate the impacts of ship traffic on North Atlantic right whales have included speed limits and routing changes. Those meant to reduce the incidence and severity of entanglements include the modification of gear design and gear deployment practices. Management measures need to be considered in advance in the Arctic in order to minimize the risks to bowhead whales as shipping and industrial fishing expand in the Arctic with ice retreat. 相似文献
12.
《Marine Policy》2013
Proponents of catch share-based fisheries have claimed ecological stewardship can result from the assignment of individual catch quotas. This claim is examined by analyzing the distribution of benthic habitat protection measures adopted by quota-owning industry sectors within the exclusive economic zones (EEZs) of the U.S. (Alaska), New Zealand, and high seas seamounts within the Southern Indian Ocean Deepsea Fishers Association (SIODFA) competence area. Results suggest the protection of both benthic ecosystems and essential fish habitat (EFH) are marginal at best when quota owners have primacy in determining the boundaries of bottom trawl closures. The majority of the areas in these three regions that are closed to trawling are too deep to fish, may not contain vulnerable marine ecosystems, and do not have high abundances of commercially important species. “Freezing the footprint” of bottom trawling is not the best method for benthic habitat protection in areas where the fishing industry is actively fishing vulnerable habitats. Analytical methods should be applied to help determine boundaries of future bottom trawl closures rather than allowing the fishing industry to place benthic protection areas (BPAs) in areas where they are not interested in fishing. 相似文献
13.
Coastal and estuarine systems provide nursery grounds for many marine fish species. Their productivity has been correlated with terrigeneous inputs entering the coastal–estuarine benthic food web, thereby favouring the establishment of fish juveniles. Studies in these ecosystems often describe the nursery as a single large habitat without verifying nor considering the presence of contiguous habitats. Our study aimed at identifying different habitats based on macrozoobenthic communities and morpho-sedimentary characteristics and assessing the trophic interactions between fish juveniles and their benthic preys within these habitats. It included 43 sampling sites covering 5 habitats in which we described taxonomically and quantitatively the invertebrates and fish communities with stable isotopes and gut contents. It suggested that the benthic common sole Solea solea displayed feeding plasticity at the population level, separating the juveniles (G0) from the older fish (G1) into different “feeding sub-populations”. Size-based feeding plasticity was also observable in the spatial occupancy of that species in the studied bay. The demersal pouting, Trisopterus luscus, equally used the different habitats but displayed low feeding plasticity across and inside each habitat. Stable isotopes proved to be powerful tools to study the spatial distribution of trophic interactions in complex ecosystems like the bay of Vilaine and to define optimal habitats for fish that use the coastal–estuarine ecosystem as nursery grounds. 相似文献
14.
In this paper we review levels of net loss, what happens to the gear once it has been lost, and the resulting levels of ‘ghost catches’ made in passive net fisheries in the EU. We also consider ghost catches resulting from lost gear in other types of fisheries, and the extent to which the value of ghost catches has been quantified. We consider why fishing gear is lost, and profile common management responses. We present a cost benefit model to assess the relative cost effectiveness of different management measures, and suggest that gear retrieval programmes may provide less value for money than other management responses. 相似文献
15.
Overexploitation of bycatch and target species in marine capture fisheries is the most widespread and direct driver of change and loss of global marine biodiversity. Bycatch in purse seine and pelagic longline tuna fisheries, the two primary gear types for catching tunas, is a primary mortality source of some populations of seabirds, sea turtles, marine mammals and sharks. Bycatch of juvenile tunas and unmarketable species and sizes of other fish in purse seine fisheries, and juvenile swordfish in longline fisheries, contributes to the overexploitation of some stocks, and is an allocation issue. There has been substantial progress in identifying gear technology solutions to seabird and sea turtle bycatch on longlines and to direct dolphin mortality in purse seines. Given sufficient investment, gear technology solutions are probably feasible for the remaining bycatch problems. More comprehensive consideration across species groups is needed to identify conflicts as well as mutual benefits from mitigation methods. Fishery-specific bycatch assessments are necessary to determine the efficacy, economic viability, practicality and safety of alternative mitigation methods. While support for gear technology research and development has generally been strong, political will to achieve broad uptake of best practices has been lacking. The five Regional Fisheries Management Organizations have achieved mixed progress mitigating bycatch. Large gaps remain in both knowledge of ecological risks and governance of bycatch. Most binding conservation and management measures fall short of gear technology best practice. A lack of performance standards, in combination with an inadequate observer coverage for all but large Pacific purse seiners, and incomplete data collection, hinders assessing measures' efficacy. Compliance is probably low due to inadequate surveillance and enforcement. Illegal, unreported and unregulated tuna fishing hampers governance efforts. Replacing consensus-based decision-making and eliminating opt-out provisions would help. Instituting rights-based management measures could elicit improved bycatch mitigation practices. While gradual improvements in an international governance of bycatch can be expected, market-based mechanisms, including retailers and their suppliers working with fisheries to gradually improve practices and governance, promise to be expeditious and effective. 相似文献
16.
Andalusia is a region of Spain with an area of some 90,000 km2 and almost 900 km length of coastline. It has an important tradition in the fishing industry that makes it one of the areas of the European Union where fisheries policies have a great significance for the population. The present statistical study deals comprehensively with the so-called “artisanal fleet”, especially in respect of data on the typology of vessels (construction particulars) and on the extractive effort made (distances and depths where they fish, duration of fishing voyages, the fishing gear used and target species), with the aim of presenting a new approach in the policies for regulating this important fisheries sector. 相似文献
17.
《Marine Policy》2017
Fatal entanglements in fishing gear threaten marine mammal populations worldwide. The management of entanglements of large whales, such as the North Atlantic right whale (Eubalaena glacialis), with commercial fisheries, is a challenge given the species’ small population size, economic consequences of regulations, and the general lack of data on entanglements. The U.S. Marine Mammal Protection Act (MMPA) requires development of programs to limit marine mammal entanglement in commercial fishing gear. Following a retrospective look at implementing aspects of the MMPA, a set of guiding principles were developed with associated best practices useful in reducing fatal large whale entanglement in fishing gear. Among these are: 1) involve stakeholders early in the decision making process; 2) establish a transparent management strategy that includes critical needs to guide research; 3) use a variety of tools such as an established process for receiving new information and ideas; and 4) incorporate adaptive management which considers the constraints of dynamic (rapid) changes to some fixed fishing gear. Efforts to reduce worldwide marine mammal bycatch will typically occur in a data-limited environment as experienced with U.S. Atlantic large whale entanglements. The guiding principles will remain as key tools for reducing large whale bycatch in fisheries as they build upon common practices. These insights developed over two decades of management can potentially help others to address similar bycatch problems. 相似文献
18.
《Marine Policy》2014
This study examined the perceptions of fishers from two fishing communities with differing use histories and involvement in the long-standing (16 yr) multiple use Mafia Island marine protected area (MIMP), Tanzania. A randomly distributed questionnaire indicated that 94% of fishers believed that without the MIMP, there would be overfishing, dynamite use, destroyed habitats, and few fish. Fishers were more positive about core zones (no-take fishery closures) than general use zones (areas allowing selective fishing) as a consequence of increases in fishing pressure. Those that reported increased catches and sizes of fish since the creation of the MIMP were more likely to agree with present zone locations and more positive in general about fisheries and conservation planning. Most thought that fish size and gear restrictions were preferable to permanent closures. Perceptions differed among communities and gear users. Community and gear type explained 46% of the variance in responses about the perception that fisheries and conservation are compatible goals. Somewhat surprisingly, these effects were more important than catch increases or involvement in MIMP-related activities. The differences in perception between communities may be partly attributed to different fishing histories. Multiple-use zoning provides a means to identify and resolve conflicts and achieve what are likely universal objectives for fisheries sustainability and conservation. 相似文献
19.
20.
A vital component of marine policy is the conservation and management of diverse marine resources. In the southeastern US, commercial fishermen target black sea bass (Centropristis striata) with pots from North Carolina to Cape Canaveral, Florida. During the fall through spring fishing season, western North Atlantic right whale (Eubalaena glacialis) distribution overlaps the black sea bass commercial pot fishery. Fishermen interviews revealed that the number of pots set ranged from 3 to 240 and the number of pots set per trawl ranged from 1 to 18. Generally, the amount of gear increased from south to north. 相似文献