首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
  相似文献   

2.
A detailed understanding of fishing activity in Scottish waters is required to inform marine spatial planning. Larger fishing vessels are fitted with Vessel Monitoring Systems (VMS) offering spatial information on fishing activity. VMS does not cover smaller vessels (under 15 m), which fish predominantly in inshore waters where the competition for space is often greatest. To improve knowledge of the distribution of fishing activity and value of fisheries in Scotland's inshore waters, Marine Scotland conducted a participatory fisheries mapping project, known as ScotMap. The data were collected during face-to-face interviews with 1090 fishermen of Scottish registered commercial fishing vessels under 15 m in overall length and relate to fishing activity for the period 2007–2011. Interviewees were asked to identify the areas in which they fish, estimate the contribution these areas make to vessel earnings, and to provide associated information. The majority of interviews relate to creel fishing. The data collected were aggregated to provide mapped outputs of the monetary value, relative importance to fishermen and the usage of the seas around Scotland (number of fishing vessels and number of crew). ScotMap outputs provide information on the locations of inshore fishing activities and the economic importance of different sea areas at a much higher spatial resolution than was previously possible. Outputs have informed marine policy development, provide a valuable resource for marine spatial planning in Scotland and illustrate how participatory mapping can generate useful resources on the location and importance of inshore fishing areas.  相似文献   

3.
Three mooring arrays were deployed in the Palamós Canyon axis with sediment traps, current meters and turbidimeters installed near the bottom and in intermediate waters. Frequent sharp and fast turbidity peaks along with current speed increases were recorded, particularly at 1200 m depth in spring and summer. During these events, near-bottom water turbidity increased by up to more than one order of magnitude, current velocity by two to four times and horizontal sediment fluxes by one to three orders of magnitude. When these events occurred, 9–11 days integrated downward particle fluxes collected by the near-bottom sediment trap increased by two to three times. These events were identified as sediment gravity flows triggered by trawling activities along the northern canyon wall. Sediment eroded by the trawling nets at 400–750 m depth on this wall seems to be channeled through a gully and transported downslope towards the canyon axis, where the 1200 m mooring was located. The sediment gravity flows recorded at the 1200 m site were not detected at deeper instrumented sites along the canyon axis, suggesting that they affect local areas of the canyon without traveling long distances downcanyon. These observations indicate that trawling can generate frequent sediment gravity flows and increase sediment fluxes locally in submarine canyons. Furthermore, in addition to the various natural processes currently causing sediment gravity flows and other sediment transport events, human activities such as trawling must be taken into account in modern submarine canyon sediment dynamics studies.  相似文献   

4.
The present investigation focuses on the effects of the stern appendages and the propulsion system on the hydro-loads generated by the propeller during off-design conditions, with particular emphasis on the in-plane components. Recent experimental investigations carried out by free running model tests [7], [8] and CFD analysis [5] for a modern twin screw model, highlighted that maneuvers at small drift angles and yaw rates might be as critical as the tighter ones due to complex propeller-wake interactions. Therefore, design criteria should take into account also these operative conditions, in order to reduce the effects of propeller-wake interaction phenomena that degrade the overall propulsive efficiency, induce shaft/hull structural vibration and increase noise emission. In the present study we analyze the effects of geometric and propulsive modifications with respect to the twin screw configuration studied in [5]. In particular, the effect of the centreline skeg, propeller direction of rotation and control strategies of the propulsion plant on the propeller bearing loads have been investigated from the analysis of the nominal wake in maneuvring conditions, computed by unsteady RANSE simulations coupled with a propeller model based on Blade Element Theory. The considered test cases were turning circle maneuvers with different rudder angles at FN = 0.265.  相似文献   

5.
Surface effect ship (SES) air cushion and seal models are implemented in an URANS hydrodynamics solver. The air cushion is modeled either as a prescribed pressure patch, or as a compressible isothermal/adiabatic ideal stagnant air with fan and leakage flows. The seals are either discretized as hinged bodies or modeled as 2D planing surfaces with hydrodynamic interaction. Verification and validation studies are performed using T-Craft experimental data for calm water resistance, sinkage and trim at Froude number (Fr) = 0.1–0.6; impulsive heave and pitch decay at Fr = 0; and wave-induced resistance and motion predictions in head waves at Fr = 0 and 0.6. The compressible air cushion model with fan and leakage flows perform better than those without the fan and leakage flows and the prescribed pressure patch model. The hinged seal model performs better than the 2D planing surface model, but is computationally expensive for time accurate simulations. Therefore, the 2D planing surface model is used for the validation studies. SES simulations on grids with 5.3 M cells show grid verification intervals of 6%, which are comparable to those reported for displacement and semi-planing hull studies on similar grid sizes. On an average calm water and impulsive motion predictions compare within 8.5% of the experimental data, and wave-induced motion predictions show somewhat larger error of 13.5%. The errors levels are mostly comparable to those for displacement and semi-planing and planing hulls. The study identifies that most critical advancement needed for SES simulations is the seal modeling including fluid structure interaction.  相似文献   

6.
A towed surface sampling device coupled to two automated flow injection analysis (FIA) systems is described. The towed system permits uncontaminated sampling of seawater from research vessels while underway at full speed. Coupling the sampler to the FIA systems permits automatic determination of Al and Fe in surface waters at natural levels at 5 min intervals, equivalent to ∼1.5 km spacing at a ship speed of 10 knots (5 m s−1). Results from the tropical Atlantic indicate significant (50%) variation in concentrations of both Al and Fe on space scales of less than 90 km. The combined system facilitates surface mapping of large regions of the ocean for dissolved Al and Fe, thus identifying the sites and magnitude of eolian deposition to the surface ocean. In combination with the determination of nutrients and other biological parameters this permits the investigation of the role that eolian deposition plays in modifying surface water biogeochemical cycles.  相似文献   

7.
The venerid clam Ruditapes philippinarum is the most prominent suspension-feeding bivalve inhabiting muddy intertidal seagrass beds in Arcachon Bay (SW France). It is exploited by fishermen, and Arcachon Bay ranks number one in France in terms of production and total biomass of this species. Previous studies revealed a decrease in the standing stock of R. philippinarum since 2003 and unbalanced length–frequency distributions with a lack of juveniles and of adults > 40 mm. Consequently, the population dynamics of this bivalve were studied at four intertidal sites and one oceanic site in Arcachon Bay. As clam size structure did not allow classical dynamics computations, field monitoring was coupled with field experiments (tagging–recapture) over two years. Monitoring of condition index and gonadal maturation stages highlighted a high variability in spawning number and intensity between sites. Recruitment events in the exploited area varied spatially but with uniformly low values. Von Bertalanffy Growth Function (VBGF) parameters (K, L∞) were determined using Appeldoorn and ELEFAN methods. In the exploited sites in the inner lagoon, K was relatively high (mean = 0.72 yr? 1) but L∞ was low (mean = 41.1 mm) resulting in a moderate growth performance index (Φ′ = 2.99). Growth parameters were not correlated with immersion time and L∞ was different between sites. Comparison of mortality coefficients (Z) between cage experiments and field monitoring suggested that fishing accounts for 65–75% of total adult mortality. Low recruitment, a low growth rate and a normal mortality rate led to low somatic production (4.1 and 8.7 g Shell-Free Dry Weight (SFDW) m? 2 yr? 1) and an annual P/B ratio from 0.44 to 0.92 yr? 1. Under current conditions, the possibility of a sustainable population in Arcachon Bay will strongly depend on recruitment success and fishing management.  相似文献   

8.
In the brackish water Baltic Sea turbot spawn at ~ 6–9 psu along the coast and on offshore banks in ICES SD 24–29, with salinity influencing the reproductive success. The potential fecundity (the stock of vitellogenic oocytes in the pre-spawning ovary), egg size (diameter and dry weight of artificially fertilized 1-day-old eggs) and gonad dry weight were assessed for fish sampled in SD 25 and SD 28. Multiple regression analysis identified somatic weight, or total length in combination with Fulton's condition factor, as main predictors of fecundity and gonad dry weight with stage of maturity (oocyte packing density or leading cohort) as an additional predictor. For egg size, somatic weight was identified as main predictor while otolith weight (proxy for age) was an additional predictor. Univariate analysis using GLM revealed significantly higher fecundity and gonad dry weight for turbot from SD 28 (3378–3474 oocytes/g somatic weight) compared to those from SD 25 (2343 oocytes/g somatic weight), with no difference in egg size (1.05 ± 0.03 mm diameter and 46.8 ± 6.5 μg dry weight; mean ± sd). The difference in egg production matched egg survival probabilities in relation to salinity conditions suggesting selection for higher fecundity as a consequence of poorer reproductive success at lower salinities. This supports the hypothesis of higher size-specific fecundity towards the limit of the distribution of a species as an adaptation to harsher environmental conditions and lower offspring survival probabilities. Within SD 28 comparisons were made between two major fishing areas targeting spawning aggregations and a marine protected area without fishing. The outcome was inconclusive and is discussed with respect to potential fishery induced effects, effects of the salinity gradient, effects of specific year-classes, and effects of maturation status of sampled fish.  相似文献   

9.
Investigations of biomass, production, and anthropogenic impact require knowledge of the spatial distribution of the species concerned. Studies of the spatial distribution of soft-sediment infauna are inherently difficult, because the organisms are generally not readily visible, necessitating painstaking excavation. Although the large-scale (tens of km) distribution patterns of infaunal bivalves have been studied previously, the fine-scale (1 to tens of meters) has received much less attention. We investigated the fine-scale spatial distribution of the edible cockle Cerastoderma edule at a fishing-impacted site and a non-impacted site on an intertidal mudflat in Bourgneuf Bay, France, in 2009–2010. A preliminary study using a 1 m spatial lag was performed to determine the optimum lags for a nested sampling design. Cohorts were identified using Bhattacharya-resolved size-frequency distributions and verification of isotropy, and the spatial characteristics of each cohort were determined using Moran's I auto-correlation coefficient. The non-impacted site presented one strongly-aggregated main cohort, C3, (Moran's I = 0.67 to − 0.34, spatial range 16 to 20 m, inter-patch distance 41 to 51 m). The impacted site presented two main cohorts, C2 (1.31 cm mean shell length, SL) and C3 (2.11 cm SL) both of which also showed a patchy spatial distribution (C2: Moran's I = 0.7 to − 0.72, spatial range 22 to 35 m; inter-patch distance 63 to 90 m; C3: Moran's I = 0.41 to − 0.63, spatial range 36 to 58 m, inter-patch distance not defined). The C3 cohort was less aggregated than the C2; possibly due to the homogenizing effect of fishing, which typically proceeds via a Lévy walk foraging model.Our results show that the spatial distributions of C. edule retained a strongly aggregated character over the 8 months of the study, suggesting that these characteristics are powerfully maintained by recruitment/post-recruitment processes, despite intense fishing pressure throughout the sampling period, and indeed for decades, prior to this study. These data also show that we cannot assume a random or a regular spatial distribution for this species in studies of biomass, production, trophic relations, or anthropogenic impact; rather, close attention must be paid to the spatial characteristics of studied populations in order to reduce the confounding effects of auto-correlation.  相似文献   

10.
The North Atlantic right whale (Eubalaena glacialis) is a critically endangered large whale species found in waters off the U.S. and Canadian Atlantic coasts. The primary human-caused threats are entanglement in fishing gear and collisions with vessels. Since 2002, NOAA's National Marine Fisheries Service has implemented both seasonally and dynamically managed protective zones where right whales occur to reduce these threats; Seasonal Area Management (SAM) and Dynamic Area Management (DAM) for the reduction of right whale entanglements with fishing gear, and Seasonal Management Areas (SMA) and Dynamic Management Areas (DMA) for reduction of vessel collisions. This paper analyzes the presence of frequent concentrations of right whales outside of SAM and SMA zones, represented by the spatial and temporal occurrence of DAMs and DMAs. A grid of 1 min×1 min squares was geospatially applied to locations of DAMs and DMAs from April 2002 through June 2011 and the number of management areas that intersected each 1 min square was populated. DAMs and DMAs were most highly concentrated along the central Gulf of Maine. Of the 131 DAMs and DMAs implemented, 97 (74.0%) intersected this area, and were primarily implemented from October through February. The results of this analysis will aid in consideration of possible modifications to the size and location of SMAs along the northern Atlantic coast of the U.S. and other management actions for the reduction of vessel collisions with right whales.  相似文献   

11.
Seven years (2001–2008) of dissolved organic carbon (DOC) vertical profiles were examined in order to assess the main processes determining DOC concentration and distribution in the meso- and bathypelagic layers of the Mediterranean Sea. As expected, DOC showed high and highly variable concentrations in the surface layer of 57–68 μM (average values between 0 and 100 m), with a decrease to 44–53 μM between 200 and 500 m. Deep DOC distribution was strongly affected by deep-water formation, with a significant increase to values of 76 μM in recently ventilated deep waters, and low concentrations, comparable to those observed in the open oceanic waters (34–45 μM), where the oldest, deep waters occurred. In winter 2004/2005 a deep-water formation event was observed and the consequent DOC export at depth was estimated to range between 0.76–3.02 Tg C month–1. In the intermediate layer, the main path of the Levantine Intermediate Water (LIW) was followed in order to estimate the DOC consumption rate in its core. Multiple regression between DOC, apparent oxygen utilization (AOU), and salinity indicated that 38% of the oxygen consumption was related to DOC mineralization when the effect of mixing was removed. In deep waters of the southern Adriatic Sea a DOC decrease of 6 μM, together with an AOU increase of 9 μM, was observed between the end of January 2008 and the end of June 2008 (5 months). These data indicate a rate of microbial utilization of DOC of about 1.2 μM C month−1, with 92% of the oxygen consumption due to DOC mineralization. These values are surprisingly high for the deep sea and represent a peculiarity of the Mediterranean Sea.  相似文献   

12.
The Benthic Boundary Layer (BBL) assemblages from the Cap-Ferret Canyon (Bay of Biscay) were quantitatively sampled at two sites located within its main channel near mooring deployments (Mooring Sites MS 1: ca. 2400 m; MS 2: ca. 3000 m) with a suprabenthic sled equipped with four nets fishing at different heights above the bottom. The macrofaunal abundance above the sea-floor was mainly represented by Isopoda (42.2%), Amphipoda (19.0%), Euphausiacea (17.3%), Cumacea (13.5%), Mysidacea (2.8%) and Tanaidacea (2.6%). At both sampling sites, the highest total densities were generally recorded in the immediate vicinity of the sea floor (10–40 cm water layer), and a drastic decrease occurred higher in the BBL community. The BBL assemblages from the two sampling sites were similar in their faunal composition (major taxa), and their mean density estimates were not statistically different (MS 1 : 525.3 ind. 100 m−2; MS 2 : 283.3 ind. m−2) although the recorded values during each cruise were always lower at the deeper site. The BBL macrofauna abundance showed obvious temporal fluctuations at both sites, probably linked with a seasonal organic input from the euphotic zone (vertical flux) via phytodetritus deposition on the sea bottom.  相似文献   

13.
Low carbon shipping research focuses on energy efficiency and mitigation measures related to operations and technology. However, reducing energy use and greenhouse gas emissions associated with a vessel’s material production receives limited attention. Material efficiency is defined as “providing material services with less material production and processing”. The current business model for ship building and breaking does not embrace fully material efficiency principles. Exploring a case study of a vessel's steel hull, this study applies a Life Cycle Assessment approach to determine the effectiveness of material efficiency to reduce CO2 emissions. When compared to Business as Usual, designing and manufacturing for 100% hull reuse provides an emissions reduction of 29% from 221,978 t CO2 to 158,285 t CO2; 50% reuse provides a 10% reduction (199,816 t CO2). From a technical and safety perspective there remain key barriers that need addressing: a vessel’s hull would require to be designed for dismantling to improve reuse; the operation and maintenance schedule must ensure the value of the steel is retained and; data must flow between key stakeholders on the quality of the steel. Despite these challenges, progressing material efficiency would require different business models that reach out and integrate the whole supply chain. There is a need for public and privately funded demonstration projects at a range of scales and markets, to provide investors the confidence that there is retained value in the steel hull when it reaches its end-of-life.  相似文献   

14.
通过对东京水产大学研究练习船“神鹰丸”的航速、主机转速、功率及排放废气的测定，得出在各种常用工况下NOx的排放率曲线、等船速曲线和燃油消耗率曲线。分析比较确定NOx的排出率较低，燃油消耗率又不超过规定标准的工况点，从而达到主机优化操纵的目的。结果表明，在自由航行工况下船舶航速为4、8、12、13kn时，主机转速应设定在750r/min；航速为10kn时，应设定在875r/min。拖网及延绳钓作业工况下主机转速应设定在875r/min。  相似文献   

15.
Direct velocity measurements undertaken using a nine-system mooring array (M1–M9) from 2004 to 2005 and two additional moorings (M7p and M8p) from 2003 to 2004 reveal the spatial and temporal properties of the deep-circulation currents southwest of the Shatsky Rise in the western North Pacific. The western branch of the deep-circulation current flowing northwestward (270–10° T) is detected almost exclusively at M2 (26°15′N), northeast of the Ogasawara Plateau. It has a width less than the 190 km distance between M1 (25°42′N) and M3 (26°48′N). The mean current speed near the bottom at M2 is 3.6±1.3 cm s?1. The eastern branch of the deep-circulation current is located at the southwestern slope of the Shatsky Rise, flowing northwestward mainly at M8 (30°48′N) on the lower part of the slope of the Shatsky Rise with a mean near-bottom speed of 5.3±1.4 cm s?1. The eastern branch often expands to M7 (30°19′N) at the foot of the rise with a mean near-bottom speed of 2.8±0.7 cm s?1 and to M9 (31°13′N) on the middle of the slope of the rise with a speed of 2.5±0.7 cm s?1 (nearly 4000 m depth); it infrequently expands furthermore to M6 (29°33′N). The width of the eastern branch is 201±70 km on average, exceeding that of the western branch. Temporal variations of the volume transports of the western and eastern branches consist of dominant variations with periods of 3 months and 1 month, varying between almost zero and significant amount; the 3-month-period variations are significantly coherent to each other with a phase lag of about 1 month for the western branch. The almost zero volume transport occurs at intervals of 2–4 months. In the eastern branch, volume transport increases with not only cross-sectional average current velocity but also current width. Because the current meters were too widely spaced to enable accurate estimates of volume transport, mean volume transport is overestimated by a factor of nearly two, yielding values of 4.1±1.2 and 9.8±1.8 Sv (1 Sv=106 m3 s?1) for the western and eastern branches, respectively. In addition, a northwestward current near the bottom at M4 (27°55′N) shows a marked variation in speed between 0 and 20 cm s?1 with a period of 45 days. This current may be part of a clockwise eddy around a seamount located immediately east of M4.  相似文献   

16.
Generally, estuarine intertidal mudflats constitute important nurseries for fish and foraging grounds for coastal birds by providing a plenitude of mollusks, worms, and crustaceans as prey, which in turn mostly feed on suspended and benthic microalgae, bacteria, and detritus. Despite the high productivity of such habitats, pronounced variability in both salinity and temperature results typically in low diversity. The only sea anemone reported from estuarine mud is the edwardsiid Nematostella vectensis Stephenson, 1935. It occurs widely in the northern hemisphere, and occasionally in extremely high density. Here we document another sea anemone from estuarine mud and muddy sand found in Southern Chile which has similar ecological attributes. Taxonomic confusion has impeded the reporting on this small but prominent member in a macrozoobenthic assemblage, the brooding Anthopleura hermaphroditica (Carlgren, 1899; Anthozoa: Actiniidae). It differs from N. vectensis by the presence of symbiotic algae. Average density under poly- to euhaline conditions in mud and muddy sand at around mid tide level was about 3 actinians per cm2. An average abundance of 11,000 m? 2, a biovolume of 487 cm3 m? 2, and a biomass of 35.5 g dry organic weight m? 2 were found in mud and muddy sand in two surveys 20 years apart. The mean fishing area of fully expanded individuals covers 42 ± 25 mm2, corresponding to a circular area with a diameter of 7.3 ± 5.7 mm. Preliminary experiments indicate that associated benthos may be relegated to life below surface by the net of tentacles above the sediment. As no predators on A. hermaphroditica could be found on the mudflat, the success of this mixotrophic sea anemone may entail a trophic dead end.  相似文献   

17.
A large bow wave forms when blunt-shaped vessels like self-propelled jack-up crane vessels (liftboats) operate at high speeds. Above a critical speed, this bow wave spills over the bow causing swamping. To investigate this phenomena, towing tank tests of a 1/25 scale model liftboat hull were done over a speed range of 3–8 kn. The test showed above 4 kn the bow wave formed and the vessel trimmed by the bow. At speeds above 8 kn the bow wave spilled over the bow (swamping). To cancel this critical bow wave a vertical bow plate was fitted ahead of the liftboat bow. This bow plate reduced the bow wave formation and achieved a 10–15% reduction in the towing resistance. The wave cancellation bow plate can reduce the liftboat power or increase its liftboat speed and operating range.  相似文献   

18.
The energy extraction performance of a flapping foil generator is studied through experiment and numerical simulation. A practical flapping foil generator has been proposed. The heave motion and the pitch motion of the foil are adjusted through a crankshaft-like structure. The heave and pitch motions of the foil are transferred to the rotational motion of the main shaft. A pair of gears is adopted to increase the pitch angle. A prototype with pitch amplitude θ0 = 60∘ has been built and the experiment is carried out in a tunnel. The overall performance of the mechanism has been analysed. Good agreement of numerical results and experiment data has been found. Further simulations with larger pitch amplitudes are carried out. It is found that higher efficiency can be achieved with larger pitch amplitude at medium frequency.  相似文献   

19.
A ship-mounted 153 kHz narrow-band ADCP and 1 m2 MOCNESS were deployed between 16 and 24 Sept. 1997 in the Ligurian central zone (∼43°20′N 7°48′E). Results from both instruments showed that the zooplankton community performed vertical migrations that conformed to the classical pattern of ascent at dusk (∼18:30 h) and descent at dawn (∼06:30 h). Depth-discrete net samples between 0 and 500 m showed that the community was dominated by two species, the euphausiid Meganyctiphanes norvegica (Northern krill) and the pteropod Cavolinia inflexa, which migrated in separate discrete bands that were detectable by the ADCP. Information from the ADCP was used to estimate vertical migration speed in two ways: (i) from the trajectory of the back-scattering bands over time and (ii) from the Doppler-shift vertical velocity measured within depth zones at the corresponding time and depth of these bands. Estimates of the migration speed of C. inflexa were between 2 and 7 cm s−1 upwards and between 4 and 7 cm s−1 downwards. M. norvegica was estimated to migrate at speeds between 7 and 8 cm s−1 upwards and over 11 cm s−1 downwards. The consistently lower migration speeds estimated from Doppler measurements as compared with estimates obtained from measuring trajectories of back-scattering bands over time was believed to result from a methodological artefact. The Doppler measurements were nevertheless useful in a relative sense in revealing the relative speed of individuals within swarms. It was shown that individuals at the front of the upwardly migrating band of M. norvegica moved more slowly than those at the rear. These results illustrate the extra biological information that can be obtained by ADCPs compared with conventional echo-sounders.  相似文献   

20.
A bioenergetic model of juvenile pink salmon (Oncorhynchus gorbuscha) was used to estimate daily prey consumption and growth potential of four ocean habitats in the Gulf of Alaska during 2001 and 2002. Growth potential was not significantly higher in 2002 than in 2001 at an alpha level of 0.05 (P=0.073). Average differences in growth potential across habitats were minimal (slope habitat=0.844 g d−1, shelf habitat=0.806 g d−1, offshore habitat=0.820 g d−1, and nearshore habitat=0.703 g d−1) and not significantly different (P=0.630). Consumption demand differed significantly between hatchery and wild stocks (P=0.035) when examined within year due to the interaction between hatchery verses wild origin and year. However, the overall effect of origin across years was not significant (P=0.705) due to similar total amounts of prey consumed by all juvenile pink salmon in both study years. We anticipated that years in which ocean survival was high would have had high growth potential, but this relationship did not prove to be true. Therefore, modeled growth potential may not be useful as a tool for forecasting survival of Prince William Sound hatchery pink salmon stocks. Significant differences in consumption demand and a two-fold difference in nearshore abundance during 2001 of hatchery and wild pink salmon confirmed the existence of strong and variable interannual competition and the importance of the nearshore region as being a potential competitive bottleneck.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号