ALBERT

Description: SUMMARY Many physical characteristics of planets, such as their topography, magnetic and gravitational fields, are routinely detected and measured by spacecrafts. At satellite altitudes, even if little is known about the measured signal, it is possible to separate the large-scale components from other contributions by a spectral analysis carried out along the spacecraft orbit. This procedure, which dates back to the early age of the satellite era, is routinely applied with spherical harmonics analysis for the study of large-scale planetary magnetic fields, particularly those that vary rapidly in time. In this paper, we review the approximations of this procedure for investigating internal and external magnetic fields of planets. We show that the magnetic field analyses along the orbits are limited by a finite frequency resolution that is known to introduce a spectral leakage. This leakage may lead to artificial spatio-temporal variations of the magnetic field, such as an apparent internal field secular variation, an asymmetry of the magnetospheric field and a regional distortion of the lithospheric field structures. We quantify the errors for the Earth’s lithospheric field and display its distribution in the spatial and the spectral domains. We also discuss these limits for the Moon and Mars lithospheric magnetic fields. Our analytical results illustrate the pros and cons of the orbit-by-orbit analyses and should allow us to avoid the pitfall of geophysical overinterpretation of some artificial magnetic field variations.

Description: We define a simple property on an infinite directed graph G and show that it is necessary and sufficient for the existence of a transient potential on the associated countable Markov shift.

Description: We consider groups G interpretable in a supersimple finite rank theory T such that T eq eliminates . It is shown that G has a definable soluble radical. If G has rank 2, then if G is pseudofinite, it is soluble-by-finite, and partial results are obtained under weaker hypotheses, such as ‘functional unimodularity’ of the theory. A classification is obtained when T is pseudofinite and G has a definable and definably primitive action on a rank 1 set.

Description: We discuss the equivalence between the categories of certain ribbon graphs and subgroups of the modular group and use this equivalence to construct exponentially large families of not Hurwitz equivalent simple braid monodromy factorizations of the same element. As an application, we also obtain exponentially large families of topologically distinct algebraic objects such as extremal elliptic surfaces, real trigonal curves, and real elliptic surfaces.

Description: In this paper, we generalize the construction of the Bloch–Kato exponential map to complete discrete valuation fields of mixed characteristic (0, p ) whose residue fields have a finite p -basis. As an application, we prove an explicit reciprocity law, generalizing Théorème IV.2.1 in [F. Cherbonnier and P. Colmez, ‘Théorie d’Iwasawa des représentations p -adiques d'un corps local', J. Amer. Math. Soc. 12 (1999) 241–268]. This result relies on the calculation of the Galois cohomology of a p -adic representation V in terms of its ( , G )-module.

Description: Given a set C R d , let p (C) be the probability that a random d -dimensional unimodular lattice, chosen according to Haar measure on SL( d , Z)\ SL( d , R), is disjoint from C \ { 0 }. For special convex sets C we prove bounds on p (C) that are sharp up to a scaling of C by a constant. We also prove bounds on a variant of p (C) where the probability is conditioned on the random lattice containing a fixed given point p != 0 . Our bounds have applications, among other things, to the asymptotic properties of the collision kernel of the periodic Lorentz gas in the Boltzmann–Grad limit, in arbitrary dimension d .

Description: SUMMARY The 2009 April 6, M w = 6.3 L’Aquila earthquake occurred within a complex system of NW–SE trending normal faults in the Abruzzi Central Apennines (Italy). We analyse the coseismic deformation as measured by 〉70 global positioning system (GPS) stations, both from continuous and survey-mode networks, providing unprecedented details for a moderate normal faulting earthquake in Italy from GPS measurements. We use rectangular, uniform-slip, dislocations embedded in an elastic, homogeneous and isotropic half-space and a constrained, non-linear optimization algorithm, to solve for the best-fitting rectangular dislocation geometry and coseismic-slip distribution. We use a bootstrap approach to investigate uncertainties in the model parameters and define confidence bounds for all the inverted parameters. The rupture occurred on a N129 °E striking and 50 ° southwestward dipping normal fault, in agreement with geological observations of surface breaks along the Paganica fault. Our distributed slip model exhibits a zone of relatively higher slip (〉60 cm) between ∼1.5 and ∼11 km depth, along a roughly downdip, NW–SE elongated patch, confined within the fault plane inverted assuming uniform-slip. The highest slip, of the order of ∼1 m, occurred on a ∼16 km 2 area located at ∼5 km depth, SE of the mainshock epicentre. The analysis of model resolution suggests that slip at depth below ∼5 km can be resolved only at a spatial scale larger than 2 km, so a finer discretization of different asperities within the main patch of coseismic-slip is not allowed by GPS data. We compute the coseismic Coulomb stress changes in the crustal volume affected by the major aftershocks, and compare the results obtained from the uniform-slip and the heterogeneous-slip models. We find that most of the large aftershocks occurred in areas of Coulomb stress increase of 0.2–13 bar and that a deepening of the slip distribution down to a depth greater than 6 km in the SE part of the fault plane, in agreement with the inverted slip model, can explain the deepest, April 7, M w 5.3 aftershock.

Description: SUMMARY The Coulomb model for stress change estimation is considered one of the most powerful physics-based forecasting tools, even though its calculations are affected by uncertainties due to the large number of a priori assumptions needed. The aim of this paper is to suggest a straightforward and reliable strategy to apply the Coulomb model for real-time forecasting. This is done by avoiding all dispensable assumptions, thus reducing the corresponding uncertainties. We demonstrate that the depth at which calculations are made is a parameter of utmost importance and apply the Coulomb model to three sequences in different tectonic regimes: Umbria-Marche (normal), Landers (strike-slip), and Chi–Chi (thrust). In each case the results confirm that when applying the Coulomb model: (i) the depth of calculation plays a fundamental role; (ii) depth uncertainties are not negligible; (iii) the best forecast at a given location is obtained by selecting the maximum stress change over the whole seismogenic depth range.

Description: SUMMARY Here, we evaluate the improvement in noise correlation functions (NCFs) gained by dividing ambient seismic records into shorter, overlapping time windows before correlation and stacking (Welch's method). We compare waveform convergence of short duration NCF stacks (e.g. 2, 5, 15 and 50 d stacks) towards the long-term (365 d) NCF stack. We observe short duration NCF improvement when applying Welch's method for non–pre-processed and running normalized time-series and short duration NCF degradation when applied to a ‘one-bit’ normalized time-series. Surprisingly, non–pre-processed time-series provides the quickest convergence to a robust (year-long) NCF. Because of the simplicity of Welch's method, the improved NCF convergence and a minimal increase in computation, we recommend applying Welch's method for future ambient seismic field analyses. Using this approach will likely improve future NCF analyses, particularly for studies with limited duration recordings, high levels of intermittent local or site noise and studies attempting to evaluate temporal variations in subsurface structure.

Description: SUMMARY Reliability diagrams are a standard forecast evaluation tool for comparing forecasted probabilities of binary events with their observed frequencies. To make this comparison for rare events, forecasts of similar probability are grouped together. Here, we demonstrate the utility of reliability diagrams for earthquake forecast evaluation with an application to a modified version of the Holliday  et al.  time-dependent earthquake forecasting method. We quantify reliability with a χ 2 statistic and find that the forecasting method is consistent with reliability; that is, forecast probabilities match rates of occurrence to within the expected uncertainties.

Description: SUMMARY In this paper, the spatial autocorrelation microtremor array analysis is utilized to map deeply-buried subtle faults that have primary controls on geothermal reservoirs. We identified a low-velocity anomaly which is approximately 50 m wide at about 550–1400 m deep. A well drilled based on this anomaly later successfully produced hot water and further proved that the low-velocity anomaly was caused by a highly fractured zone at depths from 700 to 1500 m. Our results clearly demonstrate that the microtremor survey method can be effectively utilized to map deeply-buried faults and structures for geothermal energy exploration. The most effective way to increase the drilling success rate and, hence reduce the geothermal exploration risk, seems to be the development of new exploration methods and the integration of various geophysical technologies.

Description: Glover, K. A., Skaala, Ø., Limborg, M., Kvamme, C., and Torstensen, E. Microsatellite DNA reveals population genetic differentiation among sprat ( Sprattus sprattus ) sampled throughout the Northeast Atlantic, including Norwegian fjords. – ICES Journal of Marine Science, 68: 2145–2151. Sprat ( Sprattus sprattus ), small pelagic shoaling fish, were sampled from the Celtic, North, and Baltic seas, and 10 Norwegian fjords. Significant overall genetic differentiation was observed among samples when analysed with eight microsatellite DNA loci (Global F ST = 0.0065, p 〈 0.0001). The greatest genetic differences were observed between the Baltic and all other samples (largest pairwise F ST = 0.043, p 〈 0.0001). No significant genetic differentiation was observed between a sample from the Celtic Sea (CEL) and the North Sea (NSEA; F ST = 0.001, p = 0.16), but variable levels of genetic differentiation were observed among samples collected from Norwegian fjords (pairwise F ST ranging from 0 to 0.0096, most non-significant). All fjord samples were significantly differentiated to NSEA and CEL samples. Further, all fjord samples displayed reduced allelic richness compared with NSEA and CEL samples. Clearly, sprat display population genetic differentiation throughout the Northeast Atlantic, and there may be limited connectivity between Norwegian fjord and sea-going populations.

Description: Mahévas, S., Vermard, Y., Hutton, T., Iriondo, A., Jadaud, A., Maravelias, C. D., Punzón, A., Sacchi, J., Tidd, A., Tsitsika, E., Marchal, P., Goascoz, N., Mortreux, S., and Roos, D. 2011. An investigation of human vs. technology-induced variation in catchability for a selection of European fishing fleets. – ICES Journal of Marine Science, 68: 2252–2263. The impact of the fishing effort exerted by a vessel on a population depends on catchability, which depends on population accessibility and fishing power. The work investigated whether the variation in fishing power could be the result of the technical characteristics of a vessel and/or its gear or whether it is a reflection of inter-vessel differences not accounted for by the technical attributes. These inter-vessel differences could be indicative of a skipper/crew experience effect. To improve understanding of the relationships, landings per unit effort (lpue) from logbooks and technical information on vessels and gears (collected during interviews) were used to identify variables that explained variations in fishing power. The analysis was undertaken by applying a combination of generalized additive models and generalized linear models to data from several European fleets. The study highlights the fact that taking into account information that is not routinely collected, e.g. length of headline, weight of otter boards, or type of groundrope, will significantly improve the modelled relationships between lpue and the variables that measure relative fishing power. The magnitude of the skipper/crew experience effect was weaker than the technical effect of the vessel and/or its gear.

Description: Attwood, C. G., Petersen, S. L., and Kerwath, S. E. 2011. Bycatch in South Africa's inshore trawl fishery as determined from observer records. – ICES Journal of Marine Science, 68: 2163–2174. Ship-based observer data were analysed to describe the volume, composition, utilization, and size structure of catches made by South Africa's inshore trawlers. The sampling rate was 3.5% of all trawls, including unsorted and discard samples. In all, 137 nominal species were recorded. Analysis of species composition separated the trawling grounds into seven areas, providing a framework for stratifying the ground for catch estimation and for selection of representative areas for conservation. The target species, Merluccius capensis and Austroglossus pectoralis , made up 58% of the pre-discard catch. Trachurus trachurus , Pterogymnus laniarius , Raja spp., and Chelidonichthys spp. constituted another 23%. Pre-discard catch volumes of the entire fleet were estimated. The average annual pre-discard catch of M. capensis and A. pectoralis was 9653 and 504 t, respectively, closely matching landing statistics. Argyrosomus inodorus , Rhabdosargus globiceps , Argyrozona argyrozona , and Atractoscion aequidens averaged 294, 230, 107, and 83 t annually, respectively, indicating significant overlap with the handline fishery for A. inodorus and A. argyrozona . A comparison of species composition in unsorted and discard samples revealed the species being preferentially retained. Argyrosomus inodorus and A. aequidens were trawled mainly below their size at maturity. Management needs to consider other species when determining catch or effort limits and area restrictions.

Description: Aanes, S., Nedreaas, K., and Ulvatn, S. 2011. Estimation of total retained catch based on frequency of fishing trips, inspections at sea, transhipment, and VMS data. – ICES Journal of Marine Science, 68: 1598–1605. The satellite-based vessel monitoring system in the Norwegian Economic Zone provides detailed information about individual trips by vessels. Vessel sizes are available through official registries, and the storage capacity for fish is estimated using the established conversion factors as a function of the vessel's gross registered tonnage. Scientists have had access to the database of both transport and fishing vessels, with records for individual trips, in addition to information about the total round weight (whole fish) of cod and haddock for trips inspected by the coastguard. The analysis assumes that trips with complete documentation of the fish on board are a random sample, so allowing estimation of the mean amount of both cod and haddock per trip, and annual totals give the number of trips per vessel annually. ICES has accepted this methodology for estimating illegal, unregulated, and unreported (IUU) catches, which has resulted in 15 000–166 000 t (3–35%) being added to the officially reported landings of Northeast Arctic cod during the years 2002–2008. IUU landings have decreased in recent years, but are so important for assessment and management that estimates continue to be made annually.

Description: Kindt-Larsen, L., Kirkegaard, E., and Dalskov, J. 2011. Fully documented fishery: a tool to support a catch quota management system. – ICES Journal of Marine Science, 68: 1606–1610. The Danish Government has proposed a catch quota management system (CQMS) in which fishers are obliged to report their total catches, including discards and landings, and both are counted against the formal total allowable catch (TAC). The success of a CQMS requires appropriate documentation to verify the total catch, the validity of scientific advice, and the implementation of the TACs through national catch quotas. A remote electronic monitoring (EM) system, providing full documentation of fishing operations and catches, was tested on six Danish fishing vessels operating under a CQMS for cod ( Gadus morhua ). The results showed that the EM system could provide the documentation required to support the CQMS and that it was an incentive for the participating fishers to avoid discarding cod. Changing from landings to total catch quotas would not affect the scientific-advisory processes of the International Council for the Exploration of the Sea (ICES), but it could have notable consequences for the allocation of TACs between countries.

Description: Shephard, S., Gerritsen, H. D., Kaiser, M. J., Truszkowska, H. S., and Reid, D. G. 2011. Fishing and environment drive spatial heterogeneity in Celtic Sea fish community size structure. – ICES Journal of Marine Science, 68: 2106–2113. The Large Fish Indicator (LFI) is a univariate size-based indicator of fish community state that has been selected to support the OSPAR fish community Ecological Quality Objective (EcoQO). To operate this EcoQO, a survey-based LFI for each OSPAR region needs to be developed. However, fish communities in these regions are spatially heterogeneous, and there is evidence of within-region spatial variation in the LFI that could confound an overall indicator series. For Celtic Sea trawl-survey sites, spline correlograms indicate positive spatial autocorrelation at a similar range (~40 km) for the LFI and for fishing effort (h year –1 ) from vessel monitoring systems. Statistical models reveal a strong negative effect on annual LFI by site of fishing effort within a radius of 40 km. There was a weak effect of fishing within 20 km and no effect at 10 km. LFI also varied significantly with substratum and with local fish community composition identified by a resemblance matrix derived from the survey data. Finally, there was a weak effect of survey year on LFI. Spatial stratification of LFI calculations may be necessary when developing size-based indicators for OSPAR or Marine Strategy Framework Directive regions.

Description: Petitgas, P., Doray, M., Massé, J., and Grellier, P. 2011. Spatially explicit estimation of fish length histograms, with application to anchovy habitats in the Bay of Biscay. – ICES Journal of Marine Science, 68: 2086–2095. Fish length frequency histograms from research surveys are of prime importance for identifying habitats of different life stages, as well as for stock assessment. However, no method has thus far been available for mapping these histograms as spatially varying curves. Here, a procedure is applied to map spatially connected curves, and detail is given on how it can be applied to map the length frequency histograms. At each sample location, a fish length frequency histogram is given as a vector of non-independent values. The histogram is first modelled as a polynomial expansion on the basis of orthogonal polynomials. Then, the polynomial coefficients are mapped by co-kriging, after fitting a model of co-regionalization. The length frequency map is finally derived by linearly combining maps of polynomial coefficients. An estimation variance associated with the map is also derived. Maps of anchovy length distributions are produced by applying the method to midwater trawl length data from the PELGAS acoustic surveys in the Bay of Biscay. This novel approach extends the application of kriging techniques to curves or functions, opening new perspectives for mapping more complex information than just the values of fish density.

Description: Hedger, R. D., Uglem, I., Thorstad, E. B., Finstad, B., Chittenden, C. M., Arechavala-Lopez, P., Jensen, A. J., Nilsen, R., and Økland, F. 2011. Behaviour of Atlantic cod, a marine fish predator, during Atlantic salmon post-smolt migration. – ICES Journal of Marine Science, 68: 2152–2162. Acoustic telemetry was used to determine the behavioural strategies of Atlantic cod ( Gadus morhua ) during Atlantic salmon ( Salmo salar ) post-smolt migration within a Norwegian fjord (Eresfjord). In all, 38 adult cod captured in the inner fjord were tagged with acoustic transmitters in 2008 and 2009, and their behaviour was determined using a fixed hydrophone array. Cod tended to aggregate in the innermost part of the fjord, occupying distinct demersal home territories, showing horizontal movements consistent with foraging. Tidal influences were not observed; cod spent more time near the surface at night. Cod behaviour during peak post-smolt migration differed from that before and after migration. First, cod tended to have more-focused spatial distributions during peak post-smolt migration, consistent with them not having to forage so far when prey were available in abundance. Second, some half the cod were detected nocturnally (but rarely during daylight) near the river mouth during peak post-smolt migration, consistent with them feeding on nocturnally migrating post-smolts. Third, cod were more common near the surface, consistent with them feeding on post-smolts migrating through near-surface waters. These patterns, however, were not shown by all the cod, suggesting that this opportunistic feeder was also preying on other species.

Description: Miller, E. F., Pondella II, D. J., Beck, D. S., and Herbinson, K. T. 2011. Decadal-scale changes in southern California sciaenids under different levels of harvesting pressure. – ICES Journal of Marine Science, 68: 2123–2133. A unique 38-year time-series of power-plant entrapment data collected across ~170 km of the southern California coastline was examined to describe the decadal-scale trends in common Southern California Bight sciaenid abundance in relation to oceanographic conditions. Adult catches for five of seven species declined at differing rates and severity. Declines of up to 94% were detected in historically common species such as Genyonemus lineatus , whereas historically less abundant species have increased dramatically, e.g. Umbrina roncador (2626%). Over time, the entrapped community became increasingly influenced by species with more southerly distributions, indicated by a significant decline in the average latitudinal midpoint of the community. This shift was significantly related to rising ocean temperature and took place in the early to mid-1980s. The observed species-specific abundance changes in all species except Atractoscion nobilis were significantly correlated with sea surface temperature, nearshore plankton volumetric biomass, G. lineatus or Seriphus politus nearshore larval density, or a combination of these. Patterns in A. nobilis abundance were the most isolated, likely reflecting its standing as an intensively fished species, unlike the other six species evaluated. The consistent relationship with environmental indices strongly supported the notion of a faunal shift driven by bottom-up forcing.

Description: Mikkonen, J., Keinänen, M., Casini, M., Pönni, J., and Vuorinen, P. J. 2011. Relationships between fish stock changes in the Baltic Sea and the M74 syndrome, a reproductive disorder of Atlantic salmon ( Salmo salar ). – ICES Journal of Marine Science, 68: 2134–2144. The M74 syndrome of Baltic salmon ( Salmo salar ), which appears as increased yolk-sac fry mortality (YSFM), impairs the reproduction of salmon stocks. Changes in the prey stocks of Baltic salmon in its two feeding areas, the southern Baltic Proper (BPr), where sprat ( Sprattus sprattus ) was the main prey species during the high incidence of M74, and the Bothnian Sea, where herring ( Clupea harengus ) is the dominant species, were analysed in relation to salmon growth and size and in relation to the incidence of M74. The high condition factor (CF 〉 1.05) of prespawning salmon predicted high YSFM. From the various stock factors of sprat and herring in the southern BPr, the biomass of sprat had the strongest positive relationships with the CF of prespawning salmon, and the total prey biomass with YSFM. It is concluded that the ample but unbalanced food resources for salmon in the BPr, primarily sprat, induce M74. By reducing the fishing pressure on cod ( Gadus morhua ) and by more effectively managing the sprat fishery in years when the cod stock is weak, the incidence of the M74 syndrome could be reduced and even prevented.

Description: Levesque, J. C. 2011. Commercial fisheries in the northwestern Gulf of Mexico: possible implications for conservation management at the Flower Garden Banks National Marine Sanctuary. – ICES Journal of Marine Science, 68: 2175–2190. Marine resource managers designate marine protected areas (MPAs) to conserve, protect, and enhance fragile marine resources. A form of MPAs sometimes used by resource managers in the United States is a national marine sanctuary (NMS), and for all MPAs, managers need to use updated information during sanctuary management plan reviews (MPRs). In 2006, the Flower Garden Banks NMS (FGBNMS) began its first MPR by conducting public hearings and soliciting comments. Some 66% of comments were about the potential impacts fisheries posed to the sanctuary, so a description of commercial fishery activity in the NW Gulf of Mexico can help guide resource managers make sound, informed decisions. Despite limitations on data and knowledge of fishing effort spatially for the FGBNMS, commercial landings vary by Gulf state, area, and fishing gear, with most landings from the Louisiana and Texas coasts taken with trawls and nets. The main species landed from the NW Gulf of Mexico are shrimp, yellowfin tuna, and red snapper. Some conservation measures proposed for the FGBNMS will likely impact some commercial fisheries (hook and line, bottom longline), but not others (otter trawl, pelagic longline).

Description: Lonergan, M., Duck, C. D., Thompson, D., Moss, S., and McConnell, B. 2011. British grey seal ( Halichoerus grypus ) abundance in 2008: an assessment based on aerial counts and satellite telemetry. – ICES Journal of Marine Science, 68: 2201–2209. Recent estimates of the total size of the British grey seal population have been based on fitting age-structured models to estimates of pup production. The estimates were sensitive to whether density-dependence was considered to act on fecundity or pup survival. This study provides an alternative estimate for abundance in 2008: 91 800 animals (95% confidence interval, CI , 78 400–109 900). The estimate is consistent with the results of existing models where population density influences pup survival. It suggests that reductions in fecundity are unlikely to have been the cause of the recent slowing of the rate of growth of the population. The estimate presented is based on aerial surveys of the entire Scottish coast and the east coast of England. The surveys were carried out in August of 2007–2009 and restricted to the 2 h each side of daylight low water. Data from 107 electronic tags deployed between 1995 and 2008 were used to estimate the proportion of animals hauled out during the surveys. Overall, the animals hauled out for 31% (95% CI 15–50%) of the survey windows. No significant effects on the proportion of animals hauled out were detected from year, location, age, sex, temperature, rainfall, or the timing of low tide.

Description: McGrath, S. P., Broadhurst, M. K., Butcher, P. A., and Cairns, S. C. 2011. Fate of three Australian teleosts after ingesting conventional and modified stainless- and carbon-steel hooks. – ICES Journal of Marine Science, 68: 2114–2122. In response to concerns over the fate of three Australian teleosts (mulloway, Argyrosomus japonicus , yellowfin bream, Acanthopagrus australis , and snapper, Pagrus auratus ) released with ingested recreational hooks, experiments were carried out to determine whether ejection could be promoted via different wire materials and/or their modification. Between 108 and 114 fish of each species were angled and allowed to ingest conventional or modified (with notches to reduce wire diameter by ~20%) J-hooks (~250 mm 2 ) made from three materials (stainless steel and nickel-plated and red-lacquer carbon steel), before being released into tanks and monitored with control fish for up to 61 d. Total mortalities were 35, 24, and 25% for mulloway (over 61 d), yellowfin bream (over 35 d), and snapper (over 41 d), respectively. Of the survivors, 30, 61, and 77%, respectively, ejected their hooks (and only one hook-ejected fish died). For yellowfin bream, hook ejection (and hence survival) was positively correlated with total length, and hook oxidation was the key predictor of ejection from mulloway and snapper, which could be promoted by selecting carbon-steel designs with narrow wire diameters and minimal protective coating. The choice of coating might also be important, with relatively greater mortality among mulloway and yellowfin bream that ingested nickel-plated hooks.

Description: Van Iseghem, S., Quillérou, E., Brigaudeau, C., Macher, C., Guyader, O., and Daurès, F. 2011. Ensuring representative economic data: survey data-collection methods in France for implementing the Common Fisheries Policy. – ICES Journal of Marine Science, 68: 1792–1799. Since 2001, Ifremer has implemented an economic data collection programme (EDCP) within the Data Collection Framework of the EU. It aims to obtain economic data from a sample of vessels representative of the entire French fishing fleet. This paper presents the strategies used for vessel sampling selection in the French EDCP and its implementation over several consecutive years. The approach is illustrated by the sampling plan for the fleet in the North Sea Channel Atlantic region. We show that the EDCP allows precise economic indicators such as gross revenue or fuel costs to be estimated for the whole fishing fleet, including small vessels (〈10 m), and consequently, it facilitates sound scientific advice regarding the Common Fisheries Policy. The apparent underestimation of landings by small vessels in official statistics is highlighted.

Description: Mathew, S. 2011. Fishery-dependent information and the ecosystem approach: what role can fishers and their knowledge play in developing countries? – ICES Journal of Marine Science, 68: 1805–1808. An ecosystem approach to fishery management is as much a mechanism to deal with the impact of fishing on targeted, associated, and dependent fish stocks, and on the habitat, as it is to deal with the impact of habitat degradation from natural and anthropogenic factors on fishing. In developing countries, often with little institutional capacity for generating timely and reliable information for managing fisheries, effective integration of the knowledge possessed by fishers and their communities regarding, for example, oceanographic, biological, economic, social, and cultural aspects can contribute to an ecosystem approach to fisheries. The challenge is to identify and validate such knowledge and to create policy and legal space to integrate it into management, also drawing upon good practice in industrialized countries. An attempt is made to identify such knowledge, to discuss its salient aspects, and to look at the conditions under which its practical value can be enhanced and integrated into formal fishery-management systems in developing countries.

Description: Blythe, J. N., da Silva, J. C. B., and Pineda. J. 2011. Nearshore, seasonally persistent fronts in sea surface temperature on Red Sea tropical reefs. – ICES Journal of Marine Science, 68: 1827–1832. Temperature variability was studied on tropical reefs off the coast of Saudi Arabia in the Red Sea using remote sensing from Aqua and Terra satellites. Cross-shore gradients in sea surface temperature (SST) were observed, including cold fronts (colder inshore) during winter and warm fronts (warmer inshore) during summer. Fronts persisted over synoptic and seasonal time-scales and had a periodic annual cycle over a 10-year time-series. Measurements of cross-shore SST variability were conducted at the scale of tens of kilometres, which encompassed temperature over shallow tropical reef complexes and the continental slope. Two tropical reefs that had similar reef geomorphology and offshore continental slope topography had identical cold fronts, although they were separated by 100 km along the Red Sea coast of Saudi Arabia. Satellite SST gradients across contours of topography of tropical reefs can be used as an index to flag areas potentially exposed to temperature stress.

Description: Kane, J. 2011. Multiyear variability of phytoplankton abundance in the Gulf of Maine. – ICES Journal of Marine Science, 68: 1833–1841. Significant interannual changes in phytoplankton abundance were identified in the Continuous Plankton Recorder time-series collected in the Gulf of Maine from 1961 to 2008. Abundance levels of nearly all the common taxa began to increase in 1990 and remained elevated through 2001. During that period, total numbers were above average throughout the year, with an unusual bloom in late summer. Multivariate analysis of abundance identified three consecutive multiyear periods of varying abundance levels: low to average from 1961 to 1989, above average or very high from 1990 to 2001, and below average thereafter, through 2008. Phytoplankton abundance patterns were closely aligned to the rising trends displayed by several of the common zooplankton taxa. The North Atlantic Oscillation was the only environmental variable examined that showed some association with time-series abundance trends of plankton. The index was primarily positive in the 1990s, which would favour the propagation of warm, nutrient-rich slope water into the region. Perhaps the increased influx of this water, along with feedback enrichment from abundant zooplankton stocks and reduced top-down control by the relative scarcity of the dominant copepod Calanus finmarchicus , combined with a low salinity to make the 1990s a unique decade for plankton change in the Gulf of Maine.

Description: Malyshev, A., and Quijón, P. A. 2011. Disruption of essential habitat by a coastal invader: new evidence of the effects of green crabs on eelgrass beds. – ICES Journal of Marine Science, 68: 1852–1856. Eelgrass ( Zostera marina ) beds have been declining in Atlantic Canada and elsewhere, partly as a result of sediment disruption and direct feeding/cutting of basal meristems by the green crab ( Carcinus maenas ). Green crabs are detrimental to eelgrass beds, and field and laboratory experiments have confirmed that the deleterious role of this invasive species is mediated by at least two mechanisms, depending on the size/age of the crabs: uprooting by adults and grazing by juveniles. Eelgrass uprooting and grazing by green crabs are likely to contribute to further declines or a lack of recovery of eelgrass beds.

Description: Reese, D. C., O'Malley, R. T., Brodeur, R. D., and Churnside, J. H. 2011. Epipelagic fish distributions in relation to thermal fronts in a coastal upwelling system using high-resolution remote-sensing techniques. – ICES Journal of Marine Science, 68: 1865–1874. Coastal upwelling systems are characterized by substantial spatial and temporal variability with respect to surface conditions, with fauna patchily distributed and high abundances in localized areas. Examining habitat associations on finer spatial scales than previous studies have been able to achieve would advance the understanding of important marine coastal ecosystems. This study evaluates the spatial and temporal relationships of single fish and fish schools with sea surface temperature (SST) fronts in the northern California Current upwelling system, using lidar (light detection and ranging) from an aircraft to sample surface waters over the continental shelf. High-resolution data were collected on the distribution of surface nekton and SST, then the locations of fish were analysed with respect to their proximity to SST fronts using GIS spatial analyses. Both fish schools and solitary fish were located significantly closer to fronts than would be expected by chance. The association of fish to fronts varied with the progression of the upwelling season such that fish associated less with fronts under stronger upwelling conditions. The relationships observed indicate the importance of thermal features to fish as a habitat component in a variable upwelling environment and have implications for management and conservation.

Description: Kopf, R. K., Davie, P. S., Bromhead, D., and Pepperell, J. G. 2011. Age and growth of striped marlin ( Kajikia audax ) in the Southwest Pacific Ocean. – ICES Journal of Marine Science, 68: 1884–1895. This study describes the first validated model of age and growth developed for striped marlin ( Kajikia audax ). Daily periodicity of otolith microincrements was corroborated by back-calculated hatch dates that matched the known spawning season in the Southwest Pacific Ocean (SWPO). Yearly annulus formation in fin-spine sections was corroborated by daily otolith microincrements and by a marginal increment analysis. Ages of females ranged from 140 d to 8.5 years in fish between 990 mm and 2872 mm lower-jaw fork length (LJFL), and ages of males from 130 d to 7.0 years in fish between 1120 mm and 2540 mm LJFL. Sex-specific differences in growth were significant, with females growing to a larger asymptotic size and greater age than males. An instantaneous growth rate of 3.1 mm d –1 at 6 months and an estimated length of 1422–1674 mm LJFL by age 1 year makes this species among the fastest growing bony fish. Implications of these findings are discussed in relation to commercial longline and recreational fisheries management of striped marlin in the SWPO and in relation to the biology of pelagic fish growth.

Description: Magnussen, E. 2011. Food and feeding habits of cod ( Gadus morhua ) on the Faroe Bank. – ICES Journal of Marine Science, 68: 1909–1917. Data from ten bottom surveys on the Faroe Bank during the years 1994–1998 are used to describe the feeding habits of cod on the Faroe Bank. Cod are clearly omnivorous in their diet. Overall, fish were found in 82% of the stomachs, accounting for 59% of the food by weight, but just 35% of the food items by number. Of the fish, lesser sandeel was the most common, making up 78% of the fish biomass consumed. Cannibalism was practically non-existent. In some years, the squid Loligo forbesi formed an important component of the diet, was the main food and identified in up to 64% of the stomachs, and constituting 60% by weight of the diet; in other years, it was a negligible part. Crustaceans were found in 48% of the stomachs, accounting for 16% by weight but as much as 44% by numbers. The diet of cod shifts ontogenetically, with stomach fullness greater and nutrient quality of prey higher for cod 〈70 cm.

Description: Uglem, I., Berg, M., Varne, R., Nilsen, R., Mork, J., and Bjørn, P. A. 2011. Discrimination of wild and farmed Atlantic cod ( Gadus morhua ) based on morphology and scale-circuli pattern. – ICES Journal of Marine Science, 68: 1928–1936. To evaluate the spatio–temporal distribution and ecological impacts of escaped farmed Atlantic cod ( Gadus morhua ), it is necessary that escapees can be traced in the wild. To do this, simple, reliable, and fast methods for determining the origin of cod are required. The aim of this proof-of-concept study was to evaluate whether simple analyses of scales and body morphology can distinguish between wild and farmed cod. Digital images of fish and scales from adult cod from two farms, and wild cod caught near these farms, were analysed by computer-based image analyses. By combining mean breadth of circuli and length-adjusted scale radius in a discriminant analysis, 86 and 80% of wild and farmed fish, respectively, were correctly classified. Moreover, using three simple morphometric measures representing dorsal fin size, neck curvature, and length of lower jaw, 100 and 95% of wild and farmed cod, respectively, were classified correctly. To validate these discrimination methods further, an expanded analysis of additional farmed and wild cod populations is required. The results pave the way for the development of a reliable and standardized methodology for classification of the origin of cod caught in the wild.

Description: Przeslawski, R., Currie, D. R., Sorokin, S. J., Ward. T. M., Althaus, F., and Williams, A. 2011. Utility of a spatial habitat classification system as a surrogate of marine benthic community structure for the Australian margin. – ICES Journal of Marine Science, 68: 1954–1962. This study tests whether a continental-scale classification of Australian benthic habitats (termed "seascapes") and the interpolated environmental data from which they are derived are useful as abiotic surrogates of biodiversity at a local [tens of kilometres, Great Australian Bight (GAB)] and regional scale [hundreds of kilometres, Western Australian (WA) margin]. Benthic invertebrate community structure is moderately associated with specific seascapes in both the GAB ( R = 0.418) and WA margin (excluding hard substrata, R = 0.375; all substrata, R = 0.313). Mud content, seafloor slope, and seafloor temperature are significantly correlated with invertebrate communities at both scales, with disturbance and primary production correlated with GAB communities. Seascapes are not consistently useful surrogates because the strength and significance of relationships between seascapes and community structure differs among seascapes, regions, and spatial scales. Nevertheless, a national system of seascapes is an appropriate surrogate for broad-scale benthic invertebrate community patterns when biological data are limited, provided the uncertainty is acknowledged and, where possible, an assessment made of each seascape's ability to differentiate biological communities. Further refinement of seascape derivations may include updated and additional environmental data (particularly for hard vs. soft substrata) and validation among biological datasets from a range of habitats and scales.

Description: Frie, A. K., Fagerheim, K-A., Hammill, M. O., Kapel, F. O., Lockyer, C., Stenson, G. B., Rosing-Asvid, A., and Svetochev, V. 2011. Error patterns in age estimation of harp seals ( Pagophilus groenlandicus ): results from a transatlantic, image-based, blind-reading experiment using known-age teeth. – ICES Journal of Marine Science, 68: 1942–1953. Blind readings of known-age samples are the ultimate quality control method for age estimates based on hard tissues. Unfortunately, this is often not feasible for many species because of the scarcity of known-age samples. Based on a unique collection of known-age teeth of harp seals (age range: 1–18 years), ageing errors were evaluated in relation to true age, reader experience, sex, and tooth format (images vs. originals). Bias was estimated by linear models fitted to deviations from true age, and precision was estimated as their residual standard error. Image-based blind readings of 98 tooth sections by 14 readers, representing different levels of experience, generally showed high accuracy and precision up to a seal age of ~8 years, followed by an increasingly negative bias and increased variance. Separate analyses were therefore conducted for young seals (1–7 years) and older seals. For young seals, moderate associations were found between reader experience and levels of bias, precision, and proportions of correct readings. For older seals, only precision levels showed a significant association with reader experience. Minor effects of sex and tooth format are unlikely to affect these main patterns. Observed errors, even for highly experienced readers, may affect important age-related parameters, emphasizing the importance of known-age calibration of the output from all readers.

Description: van der Kooij, J., Kupschus, S., and Scott, B. E. 2011. Delineating the habitat of demersal fish assemblages with acoustic seabed technologies. – ICES Journal of Marine Science, 68: 1973–1985. Habitats influence species distribution and, although the seabed is an important habitat factor for demersal species, traditional sampling methods often provide no practical solution to investigating the seabed over large areas. The ability of a multivariate method that utilizes single-beam acoustic seabed data combined with species composition data to define demersal fish habitats was tested. The best model explained 19.4% of the variance observed in the species data and was robust between years. Ten biotopes were identified, each containing species that, either alone or in combination with others, were indicative of that biotope. Using unclassified acoustic seabed data as explanatory variables, discrepancies between the numbers of acoustically distinct classes and species assemblages, as previously reported in the literature, were avoided, while utilizing their relationship with community structure. The study focused on the relationship between simultaneously recorded species composition and seabed data from fishing stations, but because continuous acoustic data along the survey tracks were available between stations, the model could be used to predict the spatial extent of the biotopes. Although the method was developed with the eventual aim of providing a meaningful foundation to the spatial management of mixed fisheries, it could also contribute to applications in spatial planning.

Description: Faunce, C. H., and Barbeaux, S. J. 2011. The frequency and quantity of Alaskan groundfish catcher-vessel landings made with and without an observer. – ICES Journal of Marine Science, 68: 1757–1763. The North Pacific Groundfish Observer Programme (NPGOP) is one of the largest on-board fishery-monitoring programmes in the world, and the data are used extensively for both in- and post-season management of fisheries. Within certain limits, Alaskan fishers determine when and where to carry observers. There may be an incentive to fish differently during observed trips because (i) observed trips carry higher costs than unobserved trips, and (ii) bycatch quanta for quota deduction are estimated by applying bycatch rates from observed trips to retained catches on unobserved trips. Such differences may be manifest through the skewed deployment of observers among fisheries, i.e. a deployment effect, and through unrepresentative activities by fishers when an observer is on board, i.e. an observer effect. Despite long-standing concerns expressed over the NPGOP's 40-year history, evidence of deployment and observer effects have been based largely on anecdotal information. In 2008, database changes allowed a comparison of industry landing reports for trips with and without an observer. A deployment effect was evidenced by significant deviations from the expected landing ratios between observed and unobserved trips, and linear mixed-effect models revealed differences in the landed weight and evidence for an observer effect within two of five fisheries examined.

Description: Given an integral indefinite binary Hermitian form f over an imaginary quadratic number field, we give a precise asymptotic equivalent to the number of nonequivalent representations, satisfying some congruence properties, of the rational integers with an absolute value at most s by f , as s tends to + .

Description: Kloser, R. J., Ryan, T. E., Macaulay, G. J., and Lewis, M. E. 2011. In situ measurements of target strength with optical and model verification: a case study for blue grenadier, Macruronus novaezelandiae . – ICES Journal of Marine Science, 68: 1986–1995. In situ measurements of target strength ( TS ) of isolated fish surrounding dense schools need to be representative of the schooling fish to calculate their echo-integrated biomass. Using synchronous optical and acoustic measurements from a pelagic fishing net, the standard length (81 cm, n = 128), tilt-angle (–9°), and net-disturbed in situ TS (–34.4 dB) of Australian Macruronus novaezelandiae (blue grenadier) were confirmed at depth. In situ drift experiments of assumed undisturbed but dispersed blue grenadier recorded a mean TS of –31.8 dB ( CI –33.1 to –30.9 dB) with attributed fish standard lengths of 83 cm (s.d. 7.5 cm) and weight 2.5 kg. Modelling the gasbladder showed that uncertainties in fish length, orientation, and gasbladder size could explain the differences observed. Blue grenadiers have negative buoyancy because the cavity size of their gasbladder is smaller than the volume of gas required for neutral buoyancy at depth. For the same species and length, New Zealand hoki weigh less and have smaller gasbladders than Australian blue grenadier, suggesting a conversion factor of 1.10 in length for comparative measurements. Net-attached acoustic and optical measurements indicate that model and drift in situ measurements are biased high by 2.9 and 1.0 dB, respectively. Net-attached acoustic and optical measurements are a cost-effective method of monitoring TS routinely at depth for changes in species length and weight.

Description: Let G be a connected reductive algebraic group defined over an algebraically closed field of characteristic p 〉 0. Our first aim in this note is to give concise and uniform proofs for two fundamental and deep results in the context of Serre's notion of G -complete reducibility, at the cost of less favourable bounds. Here are some special cases of these results: Suppose that the index ( H : H ° ) is prime to p and that p 〉 2 dim V –2 for some faithful G -module V . Then the following hold: (i) V is a semisimple H -module if and only if H is G -completely reducible; (ii) H ° is reductive if and only if H is G -completely reducible. We also discuss two new related results. (i) If p ≥ dim V for some G -module V and H is a G -completely reducible subgroup of G , then V is a semisimple H -module; this generalizes Jantzen's semisimplicity theorem (which is the case H = G ). (ii) If H acts semisimply on V V * for some faithful G -module V , then H is G -completely reducible.

Description: Let G be a profinite group, { X α } α be a cofiltered diagram of discrete G -spectra, and Z be a spectrum with trivial G -action. We show how to define the homotopy fixed point spectrum F ( Z , holim α X α ) hG and that when G has finite virtual cohomological dimension (vcd), it is equivalent to F ( Z , holim α ( X α ) hG ). With these tools, we show that the K ( n )-local Spanier–Whitehead dual is always a homotopy fixed point spectrum, a well-known Adams-type spectral sequence is actually a descent spectral sequence, and, for a sufficiently nice k -local profinite G -Galois extension E , with K G and closed, the equivalence (due to Behrens and the author), where denotes k -local homotopy fixed points, can be upgraded to an equivalence that just uses ordinary ( non-local ) homotopy fixed points, when G / K has finite vcd.

Description: In this paper, we study the group of self-homotopy equivalences. We prove a theorem that is analogous to Tits’ well-known theorem for linear groups. Using this result, we determine a condition for the group of self-homotopy equivalences to be of finite rank.

Description: In the present paper, we study the geometric discrepancy with respect to families of rotated rectangles. The well-known extremal cases are the axis-parallel rectangles (logarithmic discrepancy) and rectangles rotated in all possible directions (polynomial discrepancy). We study several intermediate situations: lacunary sequences of directions, lacunary sets of finite order, and sets with small Minkowski dimension. In each of these cases, extensions of a lemma due to Davenport allow us to construct appropriate rotations of the integer lattice which yield small discrepancy.

Description: We establish new results on root separation of integer, irreducible polynomials of degree at least 4. These improve earlier bounds of Bugeaud and Mignotte (for even degree) and of Beresnevich, Bernik, and Götze (for odd degree).

Description: We show that the Hochschild cohomology HH *(H) of a Hecke algebra H of finite classical type over a field k of characteristic zero and a non-zero parameter q in k is finitely generated, unless possibly if q has even order in k x and H is of type B or D .

Description: We show that Lorentzian manifolds whose isometry group is of dimension at least 1/2 n ( n –1)+1 admit different vector fields resulting in expanding, steady and shrinking Ricci solitons. Moreover, it is proved that those Ricci solitons are gradient (only) in the steady case. This provides examples of complete locally conformally flat and symmetric Lorentzian gradient Ricci solitons that are not rigid.

Description: We show that any Fermat hypercubic is apolar to a trigonal curve, and vice versa. We show also that the Waring number of the polar hypercubic associated to a tetragonal curve of genus g is at most , and for a large class of them is at most .

Description: We study the transcendence of certain Eichler integrals associated to Eisenstein series and more generally to modular forms using functional identities due to Ramanujan, Grosswald, Weil et al . The special values of such integrals at algebraic points in the upper half-plane are linked to Riemann zeta values at odd positive integers.

Description: Garcia, S. M. 2011. Potential contribution of the Internet to a global community of practice for fishery management. – ICES Journal of Marine Science, 68: 1800–1804. Managing complex socio-ecological fishery systems, following an Ecosystem Approach to Fisheries, calls for a broad range of information covering many components of the system, intensified sharing of data and knowledge (to accelerate social learning and adaptive management), and a much tighter collaboration between disciplines and stakeholders. I argue that the time has come to establish one or more communities of practice ( sensu Wenger) and that the Internet could be used efficiently for this purpose, enhancing the co-evolution of science and decision-making. Important Internet resources exist and can be mobilized, but the contribution of fishery science is still too fragmented and that of the fishing industry is embryonic. This paper suggests a web infrastructure that would facilitate the needed change.

Description: Rihan, D., Graham, N., Reid, D. G., and Lordan, C. 2011. The provision of fishery information by ICES–WGFTFB to assessment working groups: use of information and lessons learned. – ICES Journal of Marine Science, 68: 1809–1814. ICES is now asked to provide advice that is more holistic in nature, including information on the influence and effects of human activities on the marine ecosystem. From a fishing-technology perspective, this includes information on how fishers respond and adapt to changes in regulatory frameworks, the impact of technology creep, ecosystem impacts, and changes in fleet dynamics. Recognizing the importance of this, in 2005, the ICES–Food and Agriculture Organization (FAO) Working Group on Fish Technology and Fish Behaviour (WGFTFB) began to collect data and information to support scientific advice on fisheries and ecosystem issues through a questionnaire circulated to its members. The information from the questionnaires was collated by the WGFTFB and submitted in the form of summary documents to various ICES assessment working groups. This paper describes the background to this initiative, the questionnaire structure, the type of information provided, and its utility.

Description: Lorance, P., Agnarsson, S., Damalas, D., des Clers, S., Figueiredo, I., Gil, J., and Trenkel, V. M. 2011. Using qualitative and quantitative stakeholder knowledge: examples from European deep-water fisheries. – ICES Journal of Marine Science, 68: 1815–1824. Stakeholder knowledge was collected through questionnaires and cognitive maps and used to summarize biological, environmental, technical, management, and socio-economic factors for several deep-water fisheries, identifying regional management issues and solutions. The questionnaires and cognitive maps revealed different technical, environmental, and management concerns in these fisheries. Dissatisfaction with management was more at an implementation than a conceptual level, because the existing management measures were mostly considered fit for purpose. Further, catch-and-effort data provided by the fishing industry were used to calculate standardized landings per unit effort. The results suggested different trends over time for three deep-water stocks exploited by the same fleet. The examples demonstrate how stakeholder involvement and use of qualitative knowledge and quantitative data might improve the management process and stock assessments when data are limited.

Description: Chandrapavan, A., Gardner, C., Green, B. S., Linnane, A., and Hobday, D. 2011. Improving marketability through translocation: a lobster case study from southern Australia. – ICES Journal of Marine Science, 68: 1842–1851. Translocation as a method to increase the value of less-marketable, deep-water southern rock lobster Jasus edwardsii was explored. First, variation in the commercially important shell colouration and body shape between deep- and shallow-water Tasmanian populations and among South Australian and Victorian populations was quantified. Deep-water J. edwardsii were pale in colour, with longer walking legs but less meat content than shallow-water, red-coloured J. edwardsii . Traits in body shape were variable among deep-water populations across the three states and between sexes in each population. Deep-water lobsters were then translocated to a shallow-water inshore reef to determine whether the observed variation in traits was plastic and whether translocation could be used to improve the quality of deep-water lobsters. Translocated lobsters were then monitored over a 14-month post-release period, and during this time, they changed from a pale/white colour to the more marketable red colour within a single moult. Plasticity was observed in tail morphology, but not in leg morphology. The translocation experiment was successful in transforming pale/white deep-water lobsters into red lobsters with higher market value in a phenotypic response to habitat manipulation. Translocation appears to have commercial application for exploiting natural plasticity in the market traits of lobsters to increase price.

Description: Xavier, J. C., Phillips, R. A., and Cherel, Y. 2011. Cephalopods in marine predator diet assessments: why identifying upper and lower beaks is important. – ICES Journal of Marine Science, 68: 1857–1864. Cephalopods are components of the diet of many predators worldwide. They are identified mainly using their chitinized upper and lower beaks, but because it has been assumed that the number of upper and lower beaks would be the same in predator diet samples, more effort has been put into creating keys for the lower beaks, which are more easily identifiable from morphology. A test is made of whether the number of upper and lower beaks differs in diet samples collected from a major cephalopod predator, the wandering albatross ( Diomedea exulans ), potential biases in the estimation of predator diets are assessed, and upper:lower beak ratios in published studies of other seabirds, seals, whales, and fish from different parts of the world reviewed. The ratio of upper to lower beaks in diet samples from wandering albatrosses varied greatly in a single year (from 69.6% more lower beaks to 59% more upper beaks), and between years (from 0.5 to 32.1% more upper beaks), and biases were greater for certain cephalopod species, resulting in underestimation of their relative importance. Future studies need to consider using both upper and lower beaks to improve the assessment of the contribution of different cephalopods to predator diets.

Description: Burt, J. A., Feary, D. A., Bauman, A. G., Usseglio, P., Cavalcante, G. H., and Sale, P. F. 2011. Biogeographic patterns of reef fish community structure in the northeastern Arabian Peninsula. – ICES Journal of Marine Science, 68: 1875–1883. This study provides the first large-scale comparison of reef-associated fish communities in the northeastern Arabian Peninsula, with 24 sites spanning 〉3000 km of coastline in the southern Persian Gulf, the western Gulf of Oman, and the northwestern Arabian Sea, each with its own unique environmental conditions. Multivariate analyses revealed three distinct community types that were represented mainly by sites within each major water body, with 〉70% dissimilarity in community structure between each. Persian Gulf communities had low species richness, abundance, and biomass of reef fish compared with the other subregions, with communities dominated by herbivores and generalist predators that had little association with live coral. Reef fish biomass in the Gulf of Oman and Arabian Sea was comparable, and communities were dominated by fish with moderate coral association. However, there were relatively more herbivores and larger fish in the Arabian Sea than in the Gulf of Oman, where communities were dominated by planktivores. Species richness was highest in the Arabian Sea when differences in abundance among regions were accounted for. The influence of distinct environmental and oceanographic conditions on reef fish community structure in each of these areas is discussed.

Description: Chouinard, P-M., and Dutil, J-D. 2011. The structure of demersal fish assemblages in a cold, highly stratified environment. – ICES Journal of Marine Science, 68: 1896–1908. Fish are a major component of marine ecosystems, with many species co-occuring in the same habitats. Potential interactions among species and with the environment can be studied through the identification of species assemblages. Data from bottom trawl surveys (2004–2008) conducted in the estuary and northern Gulf of St Lawrence were analysed using multivariate methods (cluster, multidimensional scaling, and detrended canonical correspondence analysis) to describe the structure and composition of demersal fish assemblages, including rare and smaller non-commercial species. The spatial variability in environmental conditions that characterizes the study area has a significant impact on the composition of fish assemblages in the region. In all, 35 taxa were classified as key, and 6 main fish assemblages were described, based on catch in numbers. These assemblages had a coherent spatial distribution in the study area, associated with either depth, salinity and temperature, or dissolved oxygen. The analyses showed overall strong correlations between species abundance and prevalent environmental conditions and explained 18.4% of the variance in species abundance data and 79.2% of the variance in the species–environment relationship.

Description: Wright, P. J., Millar, C. P., and Gibb, F. M. 2011. Intrastock differences in maturation schedules of Atlantic cod, Gadus morhua . – ICES Journal of Marine Science, 68: 1918–1927. Differences in maturation schedules from three subpopulations of North Sea cod ( Gadus morhua ) were examined using the demographic probabilistic maturation reaction norm (PMRN) approach. Declines in maturation probability with size and age were evident within the North Sea cod stock, but the magnitude of decline differed among subpopulations. The difference in the rate of decline led to significant spatial differences in recent times. Changes in maturation probability could not be explained by colonization from adjacent regions indicating a local response to conditions. The greatest decline in maturation probability followed the near collapse of regional spawning biomass during the 1980s and 1990s. A new methodology was developed to integrate the effects of temperature and competitive biomass into the estimation of the PMRN. Temperature had a positive effect on maturation probability, but could only partially explain the decreasing trend in PMRN midpoints. Consequently, regional selection for early maturing genotypes provides the most parsimonious explanation for the declines in maturation probability observed. The difference in maturation probability among North Sea cod subpopulations, and the additive contribution of temperature to the estimation of change, underscores the need to account for population structuring and to incorporate temperature as a covariate in future applications of the PMRN.

Description: Da Rocha, J-M., and Gutiérrez, M-J. 2011. Lessons from the long-term management plan for northern hake: could the economic assessment have accepted it? – ICES Journal of Marine Science, 68: 1937–1941. An economic working group was convened by the EU's Scientific, Technical and Economic Committee for Fisheries (STECF) in 2007 to evaluate the potential economic consequences of the long-term management plan for the northern hake ( Merluccius merluccius ) stock. An analysis of all the scenarios proposed by the biological assessment using the Economic Interpretation of ACFM Advice (EIAA) model showed that F at the status quo level was the best policy for both yield and profits, in terms of net present values. This result is counter-intuitive because it seems to suggest that effort costs do not influence economic indicators, whereas it is widely accepted that including costs negatively affects economic indicators. A dynamic age-structured model is applied to northern hake and shows that the optimal fishing mortality that maximizes the net present value of profits is 〈 F max . The reason why the EIAA analysis was biased towards scenarios with F 〉 F max is also shown.

Description: Shephard, S., Reid, D. G., and Greenstreet, S. P. R. 2011. Interpreting the large fish indicator for the Celtic Sea. – ICES Journal of Marine Science, 68: 1963–1972. The large fish indicator (LFI) was developed in the North Sea as a size-based indicator of fish community state. It is now established as OSPAR's fish community Ecological Quality Objective (EcoQO) metric and will be applied across all OSPAR regions. To produce a protocol for use when developing regional LFIs, the North Sea experience is interpreted using data from the Celtic Sea. Differences in fish community species composition and size distribution were reflected in a different species complex and large fish threshold (50 cm) for the Celtic Sea LFI. However, a lag of 12–14 years in the relationship between assemblage-averaged fishing mortality F com, y and the LFI suggested similar underlying ecological mechanisms to the North Sea. The indicator responded to changes in small fish biomass that follow fishing-induced changes in the level of predation by large demersal piscivores. The Celtic Sea LFI showed maximum observed values 〉0.40 before 1990, and 0.40 is here proposed as an EcoQO. Development of regional LFIs demands a flexible process rather than a strictly prescriptive protocol.

Description: Welcomme, R. L. 2011. An overview of global catch statistics for inland fish. – ICES Journal of Marine Science, 68: 1751–1756. The reported global inland fish catch passed 10 million tonnes in 2008, after almost linear growth from the early 1950s. The rise coincides with an increasing number of reports of falling catches resulting from environmental degradation. It is thought that catches from inland waters were underreported in the past because of constraints on collecting the relevant data. National approaches to data collection are not generally comparable and their accuracy not usually assessed. National data processing and reporting should be audited, and training undertaken to harmonize these activities. The apparently bigger catches probably result from better reporting of actual catches rather than any increase in the amount of fish landed. Current data are sufficient only for a general overview of global inland catches of fish, rather than for the detailed analysis needed for management, policy formulation, and the valuation of inland fisheries. There is a need for improved approaches to data collection and for historical catches to be corrected to account for changes in methodologies and reporting procedures.

Description: Lam, V. W. Y., Sumaila, U. R., Dyck, A., Pauly, D., and Watson, R. 2011. Construction and first applications of a global cost of fishing database. – ICES Journal of Marine Science, 68: 1996–2004. The development of a new global database of fishing cost is described, and an overview of fishing cost patterns at national, regional, and global scales is provided. This fishing cost database provides economic information required for assessing the economics of fisheries at various scales. It covers variable and fixed costs of maritime countries, representing ~98% of global landings in 2005. Linked to country and gear-type combinations, cost estimates can be mapped to a database of spatially allocated fisheries catches for future analysis in both spatial and temporal dimensions. The global average variable cost per tonne of catch in 2005 is estimated to range between US$639 and $1217, and the total cost per tonne from $763 to $1477, with mean values of $928 and $1120, respectively. The total global variable fishing cost is estimated to be in the range US$50–96 billion per year, with a mean of $73 billion per annum in 2005 dollar equivalents.

Description: Faunce, C. H. A 2011. comparison between industry and observer catch compositions within the Gulf of Alaska rockfish fishery. – ICES Journal of Marine Science, 68: 1769–1777. Stock assessment scientists and fishery managers operate under the necessary assumption that the identities of species in official catch reports are known without error. To test this assumption, the incidence, magnitude, and possible causes of species misidentification between industry and fishery-observer data sources were investigated for 29 rockfish landings made in Kodiak, AK. Rockfish species were misidentified in nearly all these landings, and the incidence of misidentification between data sources differed among species rather than the processing plant examined. Although observers failed to identify species recorded by processing plant staff as a result of small sampling fractions, the industry missed species that were identified by observers in more than half the offloads examined. The presence of management species complexes did not reduce the likelihood of erroneous quota debiting as a result of species misidentification. In one landing, the misidentification of the main rockfish species corresponded to the release of a weekly report on total allowable catch and resulted in a delayed fishery closure. Efforts to improve the accuracy of species identifications reported by industry in landing reports are warranted in Alaska, and methods to accomplish this through efficient deployment of observers are discussed.

Description: Dynamically typed languages are becoming increasingly popular for different software development scenarios such as Web engineering, rapid prototyping or the construction of applications that require runtime adaptiveness. In contrast, statically typed languages have undeniable advantages such as early type error detection and more opportunities for compiler optimizations. Since both approaches offer different benefits, hybrid statically and dynamically typed programming languages have emerged, and some statically typed languages have also incorporated dynamic typing capabilities. In this paper, we present the minimal core of StaDyn , a hybrid typing language that performs static type inference of both statically and dynamically typed references. The type information gathered by the compiler is used to generate efficient .NET code, obtaining a significant runtime performance improvement compared with C# 4.0 and Visual Basic 10.

Description: Readahead is an important technique to deal with the huge gap between disk drives and applications. It has become a standard in modern operating systems and advanced storage systems. However, it is difficult to develop the common kernel readahead and to achieve full testing coverage of all cases. In this paper, we formulate the kernel read handling, caching and readahead behavior as an absorbing Markov decision process, and present performance evaluations to compare or verify various readaheads. We also introduce algorithms to find optimal prefetching policies for specific read pattern and present the convergence analysis. By exploiting sample-path-based methods, it becomes much easier to evaluate and optimize prefetching policies, which can provide valuable informations to help the design and improvement of practical readaheads. For illustration and verification, we present two examples and some experiments on the readaheads in Linux kernel. The results show that the model-based evaluations agree with the practice and the improved prefetching policy significantly outperforms the original one in Linux kernel for the specified workloads.

Description: Crowds must be simulated believable in terms of their appearance and behavior to improve a virtual environment's realism. Due to the complex nature of human behavior, realistic behavior of agents in crowd simulations is still a challenging problem. In this paper, we propose a novel behavioral model which builds analytical maps to control agents’ behavior adaptively with agent–crowd interaction formulations. We introduce information theoretical concepts to construct analytical maps automatically. Our model can be integrated into crowd simulators and enhance their behavioral complexity. We made comparative analyses of the presented behavior model with measured crowd data and two agent-based crowd simulators.

Description: We prove unique continuation results for the Kadomtsev–Petviashvili-I and Benjamin–Ono–Zakharov–Kuznetsov equations. Our method of proof goes back to the complex variable techniques introduced by Bourgain. The approach is quite similar to that used by Panthee for the Kadomtsev–Petviashvili-II and Zakharov–Kuznetsov equations.

Description: We prove an analogue of Farb–Masur's theorem that the length-spectrum metric on moduli space is ‘almost isometric’ to a simple model V( S ) which is induced by the cone metric over the complex of curves. As an application, we know that the Teichmüller metric and the length-spectrum metric are ‘almost isometric’ on moduli space, while they are not even quasi-isometric on Teichmüller space.

Description: In this article, we relate word and normal subgroup growth to certain functions that arise in the quantification of residual finiteness. One consequence of this endeavor is a pair of results that equate the virtual nilpotency of a finitely generated group with the asymptotic behavior of these functions. The second half of this article investigates the asymptotic behavior of two of these functions. Our main result in this area resolves a question of Bogopolski from the Kourovka notebook concerning lower bounds of one of these functions for non-abelian free groups.

Description: Let T be a torsion abelian group. We consider the class of all torsion-free abelian groups G satisfying Ext( G , T ) = 0 and search for -universal objects in this class. We show that, for certain T there is no -universal group. However, for uncountable cardinals there is always a -universal group if we assume ( V = L ). Together with results by the second author this solves completely a problem by Kulikov.

Description: We discuss necessary as well as sufficient conditions for the second iterated local multiplier algebra of a separable C *-algebra to agree with the first.

Description: We prove that certain polygons of finite groups have finitely generated infinite index normal subgroups, and are hence incoherent. This gives a new family of incoherent Kleinian groups. The method of proof suggests an effective approach toward related problems.

Description: The separable permutations are those that can be obtained from the trivial permutation by two operations called direct sum and skew sum. This class of permutations contains the class of stack sortable permutations, Av(231), which are enumerated by the Catalan numbers. We prove that all subclasses of the separable permutations which do not contain Av(231) or a symmetry of this class have rational generating functions. Our principal tools include partial well-order (the lack of an infinite antichain), atomicity (the joint embedding property), and the theory of strongly rational permutation classes which is introduced here for the first time.

Description: For a prime p and an integer u with gcd( u , p )=1, we define Fermat quotients by the conditions Heath-Brown has given a bound of exponential sums with N consecutive Fermat quotients that is non-trivial for N ≥ p 1/2+ for any fixed 〉0. We use a recent idea of Garaev together with a form of the large sieve inequality due to Baier and Zhao to show that, on average over p , one can obtain a non-trivial estimate for much shorter sums starting with N ≥ p . We also obtain lower bounds on the image size of the first N consecutive Fermat quotients and use them to prove that there is a positive integer n ≤ p 3/4+ o (1) such that q p ( n ) is a primitive root modulo p .

Description: Inspired by the swarm behaviours of social insects, research into the self-assembly of swarm robots has become an attractive issue in the robotic community. Unfortunately, there are very few platforms for self-assembly and locomotion in the field of swarm robotics. The Sambot is a novel self-assembling modular robot that shares characteristics with swarm robots and self-reconfigurable robots. Each Sambot can move autonomously and connect with the other. This paper discusses the concept of combining self-assembly and locomotion for swarm robots. Distributed control algorithms for self-assembly and locomotion are proposed. Using five physical Sambots, experiments were carried out on autonomous docking, self-assembly and locomotion. Our control algorithm for self-assembly can also be used to realize the autonomous construction and self-repair of robotic structures consisting of a large number of Sambots.

Description: A cusp form f ( z ) of weight k for SL 2 (Z) is determined uniquely by its first := dim S k Fourier coefficients. We derive an explicit bound on the n th coefficient of f in terms of its first coefficients. We use this result to study the non-negativity of the coefficients of the unique modular form of weight k with Fourier expansion In particular, we show that k =81632 is the largest weight for which all the coefficients of F k , 0 ( z ) are non-negative. This result has applications to the theory of extremal lattices.

Description: Ross and Thomas introduced the concept of slope stability to study K -stability, which has conjectural relation with the existence of constant scalar curvature Kähler metric. This paper presents a study of slope stability of Fano manifolds of dimension n ≥3 with respect to smooth curves. The question turns out to be easy for curves of genus at least 1 and the interest lies in the case of smooth rational curves. Our main result classifies completely the cases when a polarized Fano manifold ( X ,– K X ) is not slope stable with respect to a smooth curve. Our result also states that a Fano three-fold X with Picard number 1 is slope stable with respect to every smooth curve unless X is the projective space.

Description: Bollobás and Riordan introduced a three-variable polynomial extending the Tutte polynomial to oriented ribbon graphs, which are multi-graphs embedded in oriented surfaces, such that complementary regions (faces) are disks. A quasi-tree of a ribbon graph is a spanning subgraph with one face, which is described by an ordered chord diagram. By generalizing Tutte's concept of activity to quasi-trees, we prove a quasi-tree expansion of the Bollobás–Riordan–Tutte polynomial.

Description: We prove that for any finite group G , such that | G / R ( G )|〉120 (where R ( G ) is the soluble radical of G ), and any finite-dimensional vector space V on which G acts, there is a non-identity element of G with fixed-point space of dimension at least dim V . This bound is best possible.

Description: We present a method for computing the number of branches of a real analytic curve germ V ( f 1 , ..., f m ) R n ( m ≥ n ) having a singular point at the origin, and the number of half-branches of the set of double points of an analytic germ u : (R 2 , 0 ) -〉 (R 3 , 0 ).

Description: We prove that integral points can be effectively determined on all but finitely many modular curves, and on all but one modular curve of prime power level.

Description: Let K be a number field and A / K be a polarized abelian variety with absolutely trivial endomorphism ring. We show that if the Néron model of A / K has at least one fiber with potential toric dimension 1, then, for almost all rational primes , the Galois group of the splitting field of the -torsion of A is GSp 2 g (Z/).

Description: Scanning of ports on a computer occurs frequently on the Internet. An attacker performs port scans of Internet protocol addresses to find vulnerable hosts to compromise. However, it is also useful for system administrators and other network defenders to detect port scans as possible preliminaries to more serious attacks. It is a very difficult task to recognize instances of malicious port scanning. In general, a port scan may be an instance of a scan by attackers or an instance of a scan by network defenders. In this survey, we present research and development trends in this area. Our presentation includes a discussion of common port scan attacks. We provide a comparison of port scan methods based on type, mode of detection, mechanism used for detection and other characteristics. This survey also reports on the available data sets and evaluation criteria for port scan detection approaches.

Description: Proxy blind signature is an important cryptographic primitive and plays an essential role in construction of the electronic cash (e-cash). Recently, Tan (2001, An offline electronic cash scheme based on proxy blind signature. Comput. J. , 54, 505–512) proposed a new proxy blind signature scheme and applied it to electronic cash. The scheme was claimed as being provably secure under the Discrete Log assumption, DBDH assumption and Chosen–Target CDH assumption in the random oracle model. In this paper, we show that Tan's proxy blind signature scheme is insecure by demonstrating several attacks in which a malicious original signer can forge both valid proxy signature keys of arbitrary proxy signers and a proxy blind signature on an arbitrary message with respect to any proxy signer directly. We also discuss some weaknesses in the e-cash scheme proposed by Tan.

Description: In recent times, there has been increasing interest in storing data securely in the cloud environment. To provide owners of data stored in the cloud with flexible control over access to their data by other users, we propose a role-based encryption (RBE) scheme for secure cloud storage. Our scheme allows the owner of data to store it in an encrypted form in the cloud and to grant access to that data for users with specific roles. The scheme specifies a set of roles to which the users are assigned, with each role having a set of permissions. The data owner can encrypt the data and store it in the cloud in such a way that only users with specific roles can decrypt the data. Anyone else, including the cloud providers themselves, will not be able to decrypt the data. We describe such an RBE scheme using a broadcast encryption algorithm. The paper describes the security analysis of the proposed scheme and gives proofs showing that the proposed scheme is secure against attacks. We also analyse the efficiency and performance of our scheme and show that it has superior characteristics compared with other previously published schemes.

Description: Although the objective of secure communication can be achieved by using cryptographic tools, the undeniability that results from cryptographic properties may create a potential threat to the sender of the message. Unfortunately, most existing deniable protocols only provide 1-out-of-2 deniability. When both parties (the sender and the receiver) are allowed to deny generating the message, a dispute might occur between these two parties. The 1-out-of-2 deniable protocol can result in an unfair resolution of the dispute. Therefore, we propose a new model of deniability, called 1-out-of- deniability, that can provide full deniability. The 1-out-of- deniability protocol allows the originator of the message to deny that he or she generated the message, since there are an infinite number of possible message generators; at the same time, all transmitted messages can be protected and authenticated between the sender and the intended receiver. Our design can be implemented by using any public-key cryptography technique. We also analyze the correctness of the proposed protocols based on logical rules, and two practical examples are given to illustrate our design.

Description: Each year, large amounts of money and labor are spent on patching the vulnerabilities in operating systems and various popular software to prevent exploitation by worms. Modeling the propagation process can help us to devise effective strategies against those worms’ spreading. This paper presents a microcosmic analysis of worm propagation procedures. Our proposed model is different from traditional methods and examines deep inside the propagation procedure among nodes in the network by concentrating on the propagation probability and time delay described by a complex matrix. Moreover, since the analysis gives a microcosmic insight into a worm's propagation, the proposed model can avoid errors that are usually concealed in the traditional macroscopic analytical models. The objectives of this paper are to address three practical aspects of preventing worm propagation: (i) where do we patch? (ii) how many nodes do we need to patch? (iii) when do we patch? We implement a series of experiments to evaluate the effects of each major component in our microcosmic model. Based on the results drawn from the experiments, for high-risk vulnerabilities, it is critical that networks reduce the number of vulnerable nodes to below 80%. We believe our microcosmic model can benefit the security industry by allowing them to save significant money in the deployment of their security patching schemes.

Description: Although analyzing complex systems could be a complicated process, current approaches to quantify system security or vulnerability usually consider the whole system as a single component. In this paper, we propose a new compositional method to evaluate the vulnerability measure of complex systems. By the word composition we mean that the vulnerability measure of a complex system can be computed using pre-calculated vulnerability measures of its components. We define compatible systems to demonstrate which components could combine. Moreover, choice, sequential, parallel and synchronized parallel composition methods are defined and the measurement of the vulnerability in each case is presented. Our method uses a state machine to model the system. The model considers unauthorized states and attacker capabilities. Furthermore, both the probability of attack and delay time to reach the target state are used to quantify vulnerability. The proposed approach would be useful to analyze complex systems which may have complicated models. This approach reduces the state space and complexity of computation. On the other hand, if a component is replaced by another one, the vulnerability measures of other components do not change. Thus, these quantities are reused in new computation. Therefore, the calculation of the vulnerability measure for a new system is simplified.

Description: The construction of gene regulatory networks from expression data is one of the most important issues in systems biology research. However, building such networks is a tedious task, especially when both the number of genes and the complexity of gene regulation increase. In this work, we adopt the S-system model to represent the gene network and establish a methodology to infer the model. Our work mainly includes an adaptive genetic algorithm-particle swarm optimization hybrid method to infer appropriate network parameters, and a gene clustering method to decompose a large network into several smaller networks for dimension reduction. To validate the proposed methods, different series of experiments have been conducted and the results show that the proposed methods can be used to infer S-system models of gene networks efficiently and successfully.

Description: We present a content-based image retrieval system for plant image retrieval, intended especially for the house plant identification problem. A plant image consists of a collection of overlapping leaves and possibly flowers, which makes the problem challenging. We studied the suitability of various well-known color, shape and texture features for this problem, as well as introducing some new texture matching techniques and shape features. Feature extraction is applied after segmenting the plant region from the background using the max-flow min-cut technique. Results on a database of 380 plant images belonging to 78 different types of plants show promise of the proposed new techniques and the overall system: in 55% of the queries, the correct plant image is retrieved among the top-15 results. Furthermore, the accuracy goes up to 73% when a 132-image subset of well-segmented plant images are considered.

Description: We investigate the assignment of assets to tasks where each asset can potentially execute any of the tasks, but assets execute tasks with a probabilistic outcome of success. There is a cost associated with each possible assignment of an asset to a task, and if a task is not executed there is also a cost associated with the non-execution of the task. As we proposed in [Gelenbe, E., Timotheou, S., and Nicholson, D. (2010). Fast distributed near optimum assignment of assets to tasks. Comput. J., doi:10.1093/comjnl/bxq010], we formulate the allocation of assets to tasks in order to minimize the overall expected cost, as a nonlinear combinatorial optimization problem. We propose the use of network flow algorithms which are based on solving a sequence of minimum cost flow problems on appropriately constructed networks with estimated arc costs. We introduce three different schemes for the estimation of the arc costs and we investigate their performance compared with a random neural network algorithm and a greedy algorithm. We also develop an approach for obtaining tight lower bounds to the optimal solution based on a piecewise linear approximation of the considered problem.

Description: Building trust is a major concern in Peer-to-Peer networks as several kinds of applications rely on the presence of trusted services. Traditional techniques do not scale, produce very high overheads or rely on unrealistic assumptions. In this paper, we propose a new membership algorithm (Community Of Reputable PeerS, CORPS) for Distributed Hash Tables which builds a community of reputable nodes and thus enables the implementation of pseudo-trusted services. CORPS uses a reputation-based approach to decide whether a node can be a member of the group or not. We demonstrate the benefits of this approach and evaluate how much it improves the reliability of a trusted routing service.

Description: Many data sets exhibit skewed class distributions in which most cases are allocated to a class and far fewer cases to a smaller one. A classifier induced from an imbalanced data set has usually a low error rate for the majority class and an unacceptable error rate for the minority class. This paper provides a review on various methodologies that have tried to handle this problem. Afterwards, it presents an experimental study of these methodologies with a proposed cascade generalization ensemble that is applied in reweighted data and it concludes that such a framework can be a more effective solution to the problem. Our method improves the identification of a difficult small class, while keeping the classification ability of the other class in an acceptable level.

Description: Ants are generally believed to follow an intensive work routine. Numerous tales and fables refer to ants as conscientious workers. Nevertheless, biologists have discovered that ants also rest for extended periods of time. This does not only hold for individual ants. Interestingly, ant colonies exhibit synchronized activity phases that result from self-organization. In this work, self-synchronization in ant colonies is taken as the inspiring source for a new mechanism of self-synchronized duty-cycling in mobile sensor networks. Hereby, we assume that sensor nodes are equipped with energy harvesting capabilities such as, for example, solar cells. We show that the proposed self-synchronization mechanism can be made adaptive depending on variable energy resources. The main objective of this paper is to study and explore the swarm intelligence foundations of self-synchronized duty-cycling. With this purpose in mind, physical constraints such as packet collisions and packet loss are generally not considered.

Description: Vector field tomography is a field that has received considerable attention in recent decades. It deals with the problem of the determination of a vector field from non-invasive integral data. These data are modelled by the vectorial Radon transform. Previous attempts at solving this reconstruction problem showed that tomographic data alone are insufficient for determining a 2D band-limited vector field completely and uniquely. This paper describes a method that allows one to recover both components of a 2D vector field based only on integral data, by solving a system of linear equations. We carry out the analysis in the digital domain and we take advantage of the redundancy in the projection data, since these may be viewed as weighted sums of the local vector field's Cartesian components. The potential of the introduced method is demonstrated by presenting examples of vector field reconstruction.