CASE STUDIES In this case
Felix Grant delves into the real-world application of statistical software
fished areas produces smaller operational loci but increases extraction rates at the margins. Regulatory criteria which favoured removal of activity at those margins, encouraging fleets to move inward, would reduce impacts and minimise interaction between fisheries. Te resolution of VM data collection,
Fishing extraction weights by area (top) and non UK vessel activity per ICES square (bottom) in Scottish waters. (Source: Scotland’s Marine Atlas: Information for The National Marine Plan. 2011, Edinburgh: Scottish Government. ISBN 9870755982547.)
FISHING FOR DATA
Impacts of fisheries on the marine environment are a matter not just of scientific interest but of economic sustainability. Knowing how to manage these impacts means gathering geospatial and fishing intensity information on a large scale, for which reason there are vessel monitoring (VM) systems whose data are archived and, to an increasing extent, shared. From gathered data, analyses at regional, national and international scales seek to assess, amongst other things, how the choice of fishing ground definition criteria influence effects on stocks, collateral species, habitats and seabed ecologies, and so on. Tey also feed into assessments of how such criteria affect size, shape, location and overlap of actual fishing grounds in practice, across seasonal and long-term activity patterns. It seems, from these analyses, that defining a fishing ground by exclusion of infrequently
SCIENTIFIC COMPUTING WORLD
however, is an issue. If that resolution is too low, it can fail to adequately describe movements within the study space. Too high and given the large size of that study space, the costs of data collection, handling and management escalate rapidly. At present, the general scientific consensus within this field is that sampling frequency is too low for much further improvement to be researched. Increasing the resolution by raising the sampling rate would improve understanding of the detailed activity breakdown within individual fishing grounds. To assess the cost benefit balance of
different sampling rates, researchers gathered a body of high-frequency position data for comparison with existing practice on collection and analytic methods. Comparing the more exact positional information available from this high-resolution sampling with conventional predictions derived from low-resolution track interpolation showed the reliability of interpolation varied widely, depending on particular fleet behaviours. Furthermore, the differences affected
subsequent environmental impact calculations with track reconstruction from lower grid cell resolutions, producing underestimates compared to higher density sampling. A blend of higher sampling density and compensation factors would allow for this, and the researchers come to the conclusion that 30-minute data capture intervals would supply the optimum compromise between resolution and cost.
Further information: S. Jennings and J. Lee, ‘Defining fishing grounds with vessel monitoring system data’. And G. I. Lambert, et al., ‘Implications of using alternative methods of vessel monitoring system (VMS) data analysis to describe fishing activities and impacts’, both in ICES Journal of Marine Science, 2012: p.51-63 and p.fss018.
STATISTICAL PROPHYLAXIS
Ibrahim is a vet, working a rural patch in a group of East African agricultural communities. His territory is not a stereotypical picture of African poverty, with a population which is well fed and, though they have to be careful to plan ahead, reasonably secure. There are primary schools in every village and secondary education in some. On the other hand, infrastructure is thinly spread and sometimes distant. There are occasions when Ibrahim, in times of acute need, has to apply his skills to human patients. His resources, when he is at his base in a central village, include a Land Rover, a solar array backed up by a petrol generator, a small rudimentary laboratory, a laptop computer and the only telephone in the area. On the computer is installed a copy of GenStat Discovery Edition, a version of VSNi’s flagship statistical package which is freely distributed to researchers throughout the region and supported by a university several hundred kilometres away. Last year, Ibrahim began to encounter clusters of unusual acute symptoms, outside his experience and affecting farmed ungulates and the humans who tended them. Unable to identify the cause, he sent samples off for examination in the capital. Waiting for a diagnosis, which would certainly take some time and might not come at all, he turned his mind to interim measures.
Not knowing the cause, he could make no assumptions
BEYOND THE NUMBERS A STATISTICS SPECIAL 21
Further information: MathWorks
www.mathworks.co.uk/products/matlab VSN International
www.vsni.co.uk/software/genstat
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