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1.
Basic information on the distribution and habitat preferences of ecologically important species is essential for their management and protection. In the Mediterranean Sea there is increasing concern over elasmobranch species because their biological (ecological) characteristics make them highly vulnerable to fishing pressure. Their removal could affect the structure and function of marine ecosystems, inducing changes in trophic interactions at the community level due to the selective elimination of predators or prey species, competitors and species replacement. In this study Bayesian hierarchical spatial models are used to map the sensitive habitats of the three most caught elasmobranch species (Galeus melastomus, Scyliorhinus canicula, Etmopterus spinax) in the western Mediterranean Sea, based on fishery-dependent bottom trawl data. Results show that habitats associated with hard substrata and sandy beds, mainly in deep waters and with a high seabed gradient, have a greater probability registering the presence of the studied species than those associated with muddy shallow waters. Temperature and chlorophyll-α concentration show a negative relationship with S. canicula occurrence. Our results identify some of the sensitive habitats for elasmobranchs in the western Mediterranean Sea (GSA06 South), providing essential and easy-to-use interpretation tools, such as predictive distribution maps, with the final aim of improving management and conservation of these vulnerable species.  相似文献   

2.
Studies of the interactions of demersal fishing gear with the benthic environment are needed in order to manage conservation of benthic habitats. There has been limited direct assessment of these interactions through deployment of cameras on commercial fishing gear especially on demersal longlines. A compact, autonomous deep-sea video system was designed and constructed by the Australian Antarctic Division (AAD) for deployment on commercial fishing gear to observe interactions with benthos in the Southern Ocean finfish fisheries (targeting toothfish, Dissostichus spp). The Benthic Impacts Camera System (BICS) is capable of withstanding depths to 2500 m, has been successfully fitted to both longline and demersal trawl fishing gear, and is suitable for routine deployment by non-experts such as fisheries observers or crew. The system is entirely autonomous, robust, compact, easy to operate, and has minimal effect on the performance of the fishing gear it is attached to. To date, the system has successfully captured footage that demonstrates the interactions between demersal fishing gear and the benthos during routine commercial operations. It provides the first footage demonstrating the nature of the interaction between demersal longlines and benthic habitats in the Southern Ocean, as well as showing potential as a tool for rapidly assessing habitat types and presence of mobile biota such as krill (Euphausia superba).  相似文献   

3.
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   

4.
Ringnet fishing began in the early 20th century and is practised worldwide, mainly to target nearshore pelagic species. The method was introduced to Kenya’s coastal waters by migrant fishers from Tanzania. However, the impacts of this fishing gear remain poorly assessed. We assessed the spatial distribution of ringnet fishing effort and its possible effects on ecosystem components, such as coral reefs, marine megafauna and marine protected areas, on the south coast of Kenya. We tracked 89 ringnet fishing trips made from December 2015 to January 2016 and used spatial multicriteria analysis to determine hotspots of possible environmental risks. The results showed that habitat type and bathymetric profile influenced the spatial distribution of ringnet fishing effort. Mixed seagrass and coral habitats had the highest concentration of the effort. Most of the habitats in the study area were moderately exposed to the impacts of the ringnet fishery. The study identifies high-risk areas that require spatial measures to minimise possible environmental risks of the gear both to habitats and to endangered sea turtles.  相似文献   

5.
Fresh water flowing from the Arctic Ocean via the East Greenland Current influences deep water formation in the Nordic Seas as well as the salinity of the surface and deep waters flowing from there. This fresh water has three sources: Pacific water (relatively fresh cf. Atlantic water), river runoff, and sea ice meltwater. To determine the relative amounts of the three sources of fresh water, in May 2002 we collected water samples across the East Greenland Current in sections from 81.5°N to the Irminger Sea south of Denmark Strait. We used nitrate-phosphate relationships to distinguish Pacific waters from Atlantic waters, salinity to obtain the sum of sea ice melt water and river runoff water, and total alkalinity to distinguish the latter. River runoff contributed the largest part of the total fresh water component, in some regions with some inventories exceeding 12 m. Pacific fresh water (Pacific source water S ∼ 32 cf. Atlantic source water S ∼ 34.9) typically provided about 1/3 of the river runoff contribution. Sea ice meltwater was very nearly non-existent in the surface waters of all sections, likely at least in part as a result of the samples being collected before the onset of the melt season. The fresh water from the Arctic Ocean was strongly confined to near the Greenland coast. We thus conjecture that the main source of fresh water from the Arctic Ocean most strongly impacting deep convection in the Nordic Seas would be sea ice as opposed to fresh water in the liquid phase, i.e., river runoff, Pacific fresh water, and sea ice meltwater.  相似文献   

6.
The pelagic species is closely related to the marine environmental factors, and establishment of forecasting model of fishing ground with high accuracy is an important content for pelagic fishery. The chub mackerel(Scomber japonicus) in the Yellow Sea and East China Sea is an important fishing target for Chinese lighting purse seine fishery. Based on the fishery data from China's mainland large-type lighting purse seine fishery for chub mackerel during the period of 2003 to 2010 and the environmental data including sea surface temperature(SST), gradient of the sea surface temperature(GSST), sea surface height(SSH) and geostrophic velocity(GV), we attempt to establish one new forecasting model of fishing ground based on boosted regression trees. In this study, the fishing areas with fishing effort is considered as one fishing ground, and the areas with no fishing ground are randomly selected from a background field, in which the fishing areas have no records in the logbooks. The performance of the forecasting model of fishing ground is evaluated with the testing data from the actual fishing data in 2011. The results show that the forecasting model of fishing ground has a high prediction performance, and the area under receiver operating curve(AUC) attains 0.897. The predicted fishing grounds are coincided with the actual fishing locations in 2011, and the movement route is also the same as the shift of fishing vessels, which indicates that this forecasting model based on the boosted regression trees can be used to effectively forecast the fishing ground of chub mackerel in the Yellow Sea and East China Sea.  相似文献   

7.
Spatial approaches gain importance in the governance of marine practices and their environmental impacts. Harmful effects of fishing gear on marine habitats is seen as a considerable spatial conflict that needs to be resolved. One of the most severe measures is the instalment of ‘no take zones’. In the certification programme of the Marine Stewardship Council (MSC) this measure is considered to be a last resort. MSC provides a telling example of ‘informational governance’, that is, a mode of environmental governance wherein information plays a centripetal but often also contested role. Such governing through information is different from conventional state-led decision-making processes. This paper assesses the way informational processes in MSC have affected the settlement of the spatial conflict between plaice fisheries and sensitive habitats in the North Sea. It concludes that information is a formative force in bringing about sustainable fisheries but leads to different outcomes even if the target species and fishing methods are very much alike. This is due to the (nationally) specific informational interactions between non-state actors, especially fishermen and environmental Non-Governmental Organizations. Even though information in marine governance should be science-based, other information (brought in by these actors) is extremely relevant in designing spatial measures.  相似文献   

8.
Mercury speciation and its distribution in surface and deep waters of the Mediterranean Sea were studied during two oceanographic cruises on board the Italian research vessel URANIA in summer 2003 and spring 2004 as part of the Med Oceaneor and MERCYMS projects. The study included deep water profiles of dissolved gaseous Hg (DGM), reactive Hg (RHg), total Hg (THg), monomethyl Hg (MeHg) and dimethyl Hg (DMeHg) in open ocean waters. Average concentrations of measured Hg species were characterized by seasonal and spatial variations. Overall average THg concentrations ranged between 0.41 and 2.65 pM (1.32 ± 0.48 pM) and were comparable to those obtained in previous studies of the Mediterranean Sea. A significant fraction of Hg was present as “reactive” Hg (average 0.33 ± 0.32 pM). Dissolved gaseous Hg (DGM), which consists mainly of Hg0, represents a considerable proportion of THg (average 20%, 0.23 ± 0.11 pM). The portion of DGM typically increased towards the bottom, especially in areas with strong tectonic activity (Alboran Sea, Strait of Sicily, Tyrrhenian Sea), indicating its geotectonic origin. No dimethyl Hg was found in surface waters down to the depth of 40 m. Below this depth, its average concentration was 2.67 ± 2.9 fM. Dissolved fractions of total Hg and MeHg were measured in filtered water samples and were 0.68 ± 0.43 pM and 0.29 ± 0.17 pM for THg and MeHg respectively. The fraction of Hg as MeHg was in average 43%, which is relatively high compared to other ocean environments. The concentrations reported in this study are among the lowest found in marine environments and the quality of analytical methods are of key importance. Speciation of Hg in sea water is of crucial importance as THg concentrations alone do not give adequate data for understanding Hg sources and cycling in marine environments. For example, photoinduced transformations are important for the presence of reactive and elemental mercury in the surface layers, biologically mediated reactions are important for the production/degradation of MeHg and DGM in the photic zones of the water column, and the data for DGM in deep sea indicate the natural sources of Hg in geotectonicaly active areas of the Mediterranean Sea.  相似文献   

9.
为了从海量渔船轨迹数据中挖掘隐含的信息和知识,进而为渔业行政主管部门的决策提供科学依据,本研究以AIS渔船轨迹数据为研究对象,提出了一种基于深度学习和面向时空特征融合的海洋渔船密度预测方法：首先,利用渔船轨迹数据集对渔船行驶区域进行网格划分;其次,筛选出渔船高密度区域进行研究,避免数据稀疏性问题;再次,根据渔船轨迹数据的时空分析,构建三维时空融合矩阵;最后,通过卷积循环神经网络模型捕获渔船分布的时间和空间特征,并利用卷积神经网络的堆叠加强对空间特征的学习。实验通过东海海域渔船真实轨迹数据进行具体测试,结果表明渔船密度预测值与真实值非常接近,平均绝对误差为4×10-4,模型较好地拟合了渔船密度分布特征,有效地提高了渔船捕捞热点预测的准确性和鲁棒性。  相似文献   

10.
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   

11.
渔用合成纤维及其网线和绳索是构成渔具的基本要素，其强度性能对渔具的力学性能、渔获性能、使用寿命和制造成本具有重要作用。为了满足海洋渔业不断发展的需要，我国陆续颁布了一批国家及行业质量标准，并在实践中逐步接近ＩＳＯ标准或国际名牌产品标准，使渔具纤维材料性能有了较大的提高。本文通过对国内外渔具合成纤维材料强度性能的比较和分析，认为：（１）国产合成纤维长丝的有关性能与日本产品无显著差异；（２）国产ＰＡ胶丝性能普遍较好，并优于英国产品，而ＰＡ长丝捻线与国外产品尚有较大差距；（３）ＰＥ线产品性能普遍超过ＱＪ／ＣＮＦＣ０２９２标准，但仍低于ＳＣ１４１—８５标准要求；（４）国产ＰＡ长丝三股绳索性能与德国产品接近而高于日本产品；（５）ＰＥ和ＰＶＡ三股绳索性能仅略高于日本产品；（６）渔具新材料的研制及其在渔业中的开发应用与国外相比，尚有较大差距，应得到足够重视。  相似文献   

12.
Extensive areas of methane-derived authigenic carbonate (MDAC) have been mapped in the Irish Sea. In the Irish Sector, 23 seabed mounds associated with the Codling Fault Zone were identified by multi-beam echo sounder mapping. Inspection by ROV-mounted video showed that these mounds are rocky features rising 5–10 m above the normal seabed; sampling showed that they are comprised of quartz grains bound together by carbonate cement, probably MDAC. Two separate locations have been mapped in the UK Sector. At Texel 11, seabed mounds and a 6–8 m high cliff were mapped geophysically (MBES, SSS and seismic profiler surveys). Video surveys showed that both the mounds and the cliff are rocky reefs colonised by a prolific fauna. Samples proved to be carbonate-cemented sediments, and carbon isotope analysis (δ13C −41 to −46% PDB) showed that the cement was MDAC. Similar surveys of the Holden’s Reefs area proved the presence of similar rocky reefs which are also cemented by MDAC. The total area covered by these two MDAC occurrences is estimated to be >500,000 m2. These MDAC occurrences are comparable in nature and formation to the ‘bubbling reefs’ of the Kattegat. As the bubbling reefs are “seabed features formed by leaking gas”, one of the marine habitats identified by the European Commission’s Habitats Directive as being sensitive and worthy of protection, it is suggested that the Irish Sea carbonate reefs should also be considered as special habitats.  相似文献   

13.
The seas in North-East Asia, the Yellow/East China Sea and the East Sea, which are semi-enclosed seas constituting unitary ecosystems are now facing many problems such as depletion of fish stocks, poor fishery management policies, and large-scale deterioration of the marine environment. The fishery resources of the region have long been subject to heavy fishing pressures, and many stocks are now believed to be seriously depleted and may be in danger of extinction because of overfishing. In addition, poor fishery management policies have accelerated overfishing and the rapid depletion of fish stocks. Considering this rapidly deteriorating situation, regional co-operation based on the 1982 UN Convention among coastal states should be given top priority. Most fish stocks in the region migrate beyond the jurisdiction of any one country. Indeed, one state by itself can easily destroy fishery resources because semi-enclosed seas, particularly those such as the Yellow/East China Sea and the East Sea, cannot be managed effectively without close co-operation among the coastal states.  相似文献   

14.
Total suspended matter was collected along the Yangtze River (Changjiang) and in the East China Sea in April to May and in September 2003, respectively, to study origin and fate of particulate organic nitrogen. Concentrations of particulate organic carbon (POC), nitrogen (PN) and hydrolyzable particulate amino acids (PAA; d- and l-enantiomers) were higher in the Yangtze Estuary than in the river and decreased offshore towards the shelf edge. In the coastal area, higher values of PAA were observed in the surface layer than in the bottom water. Stable carbon isotope ratios (δ13C) of POC increased from − 24.4‰ in the river to values around − 21‰ on the East China Sea Shelf. Dominant amino acids were aspartic acid + aspartine (Asx), glutamic acid + glutamine (Glx), glycine, alanine and serine. The proportions of Asx, Glx and isoleucine were higher in the marine than in the riverine samples contrary to the distributions of glycine, alanine, threonine and arginine. The proportions of d-amino acids were highest in the riverine suspended organic matter (6% of PAA) decreasing towards the shelf edge (1.5% of PAA). d-arginine, not reported in natural aquatic samples so far, was the most abundant d-amino acid in the river. The amino acid composition of the particulate organic matter (POM) in the Yangtze River indicates an advanced stage of degradation of POM. Highly degraded organic matter from soils is probably a main source of POM in the Yangtze River, but the relatively high δ13C values and low C/N ratios (7.7 ± 1.6) also indicate contribution from anthropogenic sources. The degraded riverine material was a dominant organic matter source in the estuary, where aquatic primary production had only a small overall contribution. In the East China Sea, gradual settling of riverine organic matter and the addition of fresher phytoplankton impacted the amino acid composition and δ13C values, and on the outer shelf relatively fresh phytoplankton-derived organic matter dominated.  相似文献   

15.
This study presents the first comprehensive estimation of discard amounts in the Galician fishing fleet, in order to provide an integral view of this increasing environmental problem at a regional scale. Subsequently, a series of improvement actions relating to discard minimization are suggested with the goal of enhancing the performance of the Galician fishing fleet through discard minimization. Discard estimates were constructed individually for the different Galician fisheries by aggregating primary data obtained from a total of 89 fishing vessels and secondary data for those fleets that were not directly sampled. Results showed that roughly 60,250 t of marine organisms were discarded by the Galician fleet in 2008, representing 16.9% of the total capture. Moreover, an important percentage of these discards were linked mainly to trawling vessels and to a lesser extent, to certain long lining fisheries. Therefore, improved management measures in target stocks should take into account the fact that alternative fishing gears other than trawl nets may reduce the amount of discards for certain species. This estimation may improve the assessment of stocks and help to quantify the damage that discards may have on wild ecosystems.  相似文献   

16.
It is widely documented that marine debris is detrimental to the marine ecological environment. While there are various sources of marine debris, that generated by ships constitutes a significant proportion. Annex V of MARPOL 73/78 is to regulate the discharge of garbage from ships; in particular, it prohibits all kinds of plastics from being discharged into ocean. However, most fishing vessels are virtually exempt from such regulations due to their low gross tonnage, below 400 t. Given the great number of fishing vessels operating around the world, it can be argued that fishing vessels are a common source of marine debris. This paper aims to propose measures that will fill the gap in international regulations in addressing the problem of vessel-source garbage pollution. An understanding of what constitutes the underlying causes leading to fishers' decision on debris disposal is needed when designing effective measures to reduce garbage pollution from ships. Thus, this paper seeks to identify factors that have the potential to influence fishers' disposal behavior and investigate the association between factors and fishers' intention of bringing garbage back to port. Major factors of a well-developed recycling practice, adequate collection facilities placed at port, fishers' positive views towards marine environments and provision of rewards are identified, which have significant implications for management strategies. Finally, the papers offers suggestions regarding future efforts focusing on debris reduction strategies to further address the problem of garbage pollution from fishing vessels.  相似文献   

17.
Temporarily open/closed estuaries typically open to the sea due to freshwater inflow coupled with storm surge events. In September 2008, in the absence of freshwater inflow, the mouth of the East Kleinemonde Estuary breached in response to a storm surge. The mouth of the estuary closed the following day at a high level. Marine overwash events following the breach introduced large volumes of saline water into the estuary and raised the water level by 0.07–0.33 m. Salinity was significantly higher in the 15 month closed phase after the breach (31 ± 0.9) compared to 21.9 ± 0.9 in the closed brackish phase before the breach. The historical average salinity for the estuary during a closed period is 23–25. The increase in salinity has reduced submerged macrophytes Ruppia cirrhosa and Chara vulgaris cover by 38.1%. Macroalgal cover of species such as Dictyota dichotoma, Caulacanthus ustulatus, Codium tenue and Ulva spp. have increased by 7.9%. The saline high water levels have also significantly reduced supratidal salt marsh cover by 15.2%, and reed and sedge cover by 19.7%. Loss of these habitats may result in bank destabilisation and erosion. This is the first record of an extended saline period in the 15 years the estuary has been monitored. Sea level rise in association with climate change, together with localised freshwater inflow reduction is likely to result in an increase in marine overwash events. The frequency and duration of closed saline periods are likely to increase in this type of estuary. A loss of submerged macrophytes may have significant impacts on faunal composition and abundance and on the subsequent functioning of temporarily open/closed estuaries. This has serious ecological implications since these estuaries represent 70% of the different types of estuaries found in South Africa.  相似文献   

18.
中国近海区域古菌群落结构研究概述   总被引：3，自引：0，他引：3  
古菌作为海洋微生物的重要组成部分,是海洋生态系统中物质与能量传递的重要贡献者,在全球生物地球化学循环中扮演着不可或缺的角色。虽然目前绝大多数的古菌尚未获得纯培养,但近年来分子生物学技术的发展使人们认识到古菌参与甚至主导了海洋生源要素循环的关键过程。本文介绍了目前研究海洋古菌多样性的主要手段,包括:荧光定量PCR、16S rRNA基因扩增子高通量测序、宏组学以及单细胞测序等技术,系统地阐述了中国近海不同区域(包括辽河口、黄河口、渤海、南北黄海、长江口、东海北部、珠江口以及南海区域)海水及沉积物中的古菌群落结构和多样性特征。研究表明我国近海地区的主要古菌类群为广古菌门(Euryarchaeota)、奇古菌门(Thaumarchaeota)、乌斯古菌门(Woesearchaeota)和深古菌门(Bathyarchaeota)等,其生物地理学分布主要受到环境因子和距离因素的影响,且在河口和近海海域呈现出完全不同的分布特点。在此基础上,对未来的研究方向进行展望,为全面深入了解我国边缘海生态系统中古菌群落及其参与的生物地球化学循环奠定了基础。  相似文献   

19.
The improvement of fishing technology has been detrimental to the sustainability of fisheries, which is particularly clear for the bottom trawl fishery. Reducing its environmental impact is a key point for the development of a more sustainable fishery. The present work analyzed different possibilities to mitigate the impact of gears on the seabed and to increase the efficiency of the bottom trawl fishery of the Western Mediterranean. The analysis of three experiments showed that innovative technical and regulation measures can lead to benefits such as the reduction of fishing effort, the improvement of the cost-benefit relation and the reduction of the direct impact on the seabed and the indirect effect on the ecosystems through reduce discards and the emission of CO2 into the atmosphere. After years of studies focused on improving the sustainability of this fishery, it's about time to turn this improvement into reality.  相似文献   

20.
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   

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