Research Document - 2013/019
A re-analysis of northern Hudson Bay narwhal surveys conducted in 1982, 2000, and 2011
By N.C. Asselin and S.H. Ferguson
Abstract
Assessing trends associated with long-term monitoring of the abundance of wildlife populations is partly hindered by differences in methodologies as new techniques and equipment are developed. The Northern Hudson Bay (NHB) narwhal population was surveyed in the early 1980s, 2000, and 2011. The three estimate methodologies (from the 1980s, 2000, and 2011) varied in terms of spatial extent, data collection, and analysis. The 2011 visual survey data were re-analysed using the methods of the visual surveys in 1982 and 2000. The ratios of the 2011 abundance results to those that would have been obtained using the methods from 1982 and 2000 were calculated. The 1982, 2000, and 2011 analysis methods, when applied to the 2011 survey data, yielded surface estimates of 1737 (95% Confidence Interval (C.I.) 1002-3011), 1945 (95% C.I. 1089-3471) and 4452 (95% C.I. 2707-7322) narwhals, respectively. The ratios of the 2011 to the 1982 and 2000 surface estimates were 2.56 and 2.29, respectively. These ratios show that large differences in estimates of abundance can be associated with the use of different survey and analysis methods. Nevertheless, these survey ratios assist in assessing trends in the NHB narwhal population by accounting for changes in methodologies over time.
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