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Please use this identifier to cite or link to this item: http://hdl.handle.net/10023/632
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CREEM_technical_report_2007_4_Investigation of towed hydrophone monitoring power .pdf314.25 kBAdobe PDFView/Open
Title: Investigation of towed hydrophone monitoring power for harbour porpoise on the SCANS II survey.
Authors: Borchers, David L.
Burt, M. Louise.
Keywords: statistical power
monitoring
wildlife population assessment
distance sampling
trend estimation
Issue Date: 2007
Citation: CREEM technical report ; 2007-04
Abstract: We investigate the power of harbour porpoise monitoring programmes which use an index of relative abundance to detect change. Power depends on the variability in the constant of proportionality relating the index to absolute abundance, as well as on the variability in the index given this constant. We estimate both from the SCANS II data and from European Seabirds at Sea (ESAS) data. Estimates of the coefficient of variation of the constant of proportionality are large and this results in very low power. Because these estimates may be unrealistically large for well-designed monitoring programs, we feel it is inappropriate to draw strong conclusions about the power of future monitoring programmes based on them. ESAS surveys are found to be more efficient in terms of effort required to achieve given power, than the SCANS II passive acoustic surveys. However, the comparison may not be a fair one, for the following reason. The estimated CV of the constant of proportionality is obtained from the ratio of the index of density and the corresponding SCANS II absolute density estimate; the ESAS index is likely to be more highly correlated with the SCANS II estimate than the acoustic index, because like the SCANS II estimate, it is based on visual detections. In addition, standardization of the passive acoustic survey methods could yield substantially higher efficiency. We provide a table giving power as a function of the CV of the constant of proportionality and the CV of the index, given this constant - this can be used to compare methods if reliable estimates of these CVs are available.
Version: Postprint
Description: Previously in the University eprints HAIRST pilot service at http://eprints.st-andrews.ac.uk/archive/00000457/
URI: http://hdl.handle.net/10023/632
Type: Report
Publication Status: Not published
Status: Non peer reviewed
Publisher: CREEM, University of St Andrews
Appears in Collections:Centre for Research into Ecological & Environmental Modelling (CREEM) Technical report series



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