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  • 2010-2014  (5)
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  • 1
    Publication Date: 2012-04-10
    Description: Lambert, G. I., Hiddink, J. G., Hintzen, N. T., Hinz, H., Kaiser, M. J., Murray, L. G., and Jennings, S. 2012. Implications of using alternative methods of vessel monitoring system (VMS) data analysis to describe fishing activities and impacts. – ICES Journal of Marine Science, 69: 682–693. Understanding the spatial distribution and intensity of fishing activity is a prerequisite for estimating fishing impacts on seabed biota and habitats. Vessel monitoring system data provide information on fishing activity at large spatial scales. However, successive position records can be too infrequent to describe the complex movements fishing vessels make. High-frequency position data were collected to evaluate how polling frequency and the method of analysis influenced the estimates of fishing impact on the seabed and associated epifaunal communities. Comparisons of known positions with predictions from track interpolation revealed that the performance of interpolation depended on fleet behaviour. Descriptions and indicators of fishing intensity were influenced significantly by the analytical methods (track reconstruction, density of position records) and grid-cell resolution used for the analysis. These factors can lead to an underestimation of fishing impact on epifaunal communities. It is necessary to correct for such errors to quantify the effects of fishing on various ecosystem components and hence to inform ecosystem-based management. Polling at intervals of 30 min would provide a desirable compromise between achieving precise estimates of fishing impacts on the seabed and minimizing the cost of data collection and handling.
    Print ISSN: 1054-3139
    Electronic ISSN: 1095-9289
    Topics: Biology , Geosciences , Physics
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  • 2
    Publication Date: 2011-11-24
    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.
    Print ISSN: 1054-3139
    Electronic ISSN: 1095-9289
    Topics: Biology , Geosciences , Physics
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  • 3
    Publication Date: 2013-10-15
    Description: Murray, L. G., Hinz, H., Hold, N., and Kaiser, M. J. 2013. The effectiveness of using CPUE data derived from Vessel Monitoring Systems and fisheries logbooks to estimate scallop biomass. – ICES Journal of Marine Science, 70: . Obtaining accurate data on abundance is vital to undertaking viable stock assessments of commercially exploited species. Satellite Vessel Monitoring Systems (VMSs) combined with fisheries logbooks have the potential to provide an abundant source of data with greater spatial and temporal coverage than research surveys. However, to date it has not been demonstrated how well VMS-derived abundance or biomass indices reflect research survey results. In this study we compared biomass indices of scallops derived from (i) fishing vessel surveys, (ii) research vessel surveys, and (iii) fishery-dependent data using VMSs and logbooks. In most cases there were strong relationships between biomass indices of Pecten maximus from fishing vessels and the research vessel. There were stronger relationships between P. maximus biomass indices from fishery-dependent VMS and logbook data and research vessel data at the beginning of the fishing season, when abundance was higher, but weaker relationships at the end of the fishing season. The time and location of sampling affected biomass estimates over short periods, and without standardizing to location and vessel, biomass depletion was masked. Fishery-dependent data provides a valid means of assessing relative scallop abundance and may prove equally viable in other fisheries with appropriate standardization of Catch Per Unit Effort (CPUE) data, making real-time management of fisheries increasingly feasible.
    Print ISSN: 1054-3139
    Electronic ISSN: 1095-9289
    Topics: Biology , Geosciences , Physics
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  • 4
    Publication Date: 2011-12-10
    Description: Recent theoretical studies have shown the feasibility and potential scientific value of radio tomographic imaging of Earth's magnetosphere by measuring Faraday rotation and phase difference (or group delay) of coherent radio wave signals. On 15 August 2000, a 6 W linearly polarized 828 kHz signal transmitted by the Radio Plasma Imager (RPI) on the IMAGE spacecraft was clearly detected by WAVES X and Z antennas on Wind spacecraft. Following our previous analysis of the path-integrated product change of the magnetic field and plasma density based on the spin rate measurement, we report here Faraday rotation measured from absolute antenna orientation using the phase difference between the spin-phase modeled RPI signal and the WAVES X- and Z-antenna received RPI signals. The new approach gives Faraday rotation without the mod (π) ambiguity. The average electron density extracted along a typical signal propagation path over a 1 hour measurement window agrees well with empirical models of the northern polar region derived from years of measurements. Finally, we demonstrate preliminary 2-D radio tomographic imaging of magnetospheric plasma density using the Faraday rotation measurement.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2011-05-10
    Print ISSN: 1754-9957
    Electronic ISSN: 1754-9965
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Law , Economics
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