Free access article

Issue Aquat. Living Resour. Volume 22, Number 2, April-June 2009 Fish Stock Assessments Using Surveys and Indicators Page(s) 173 - 185 DOI 10.1051/alr/2009019 Published online 17 June 2009

Aquat. Living Resour. 22 (2009) 173-185
DOI: 10.1051/alr/2009019

A selection of nonparametric statistical methods for assessing trends in trawl survey indicators as part of an ecosystem approach to fisheries management (EAFM)

John Cotter

Centre for Environment, Fisheries and Aquaculture Science Lowestoft, NR33 0HT, UK

Received 23 June 2008; Accepted 27 February 2009 ; Published online 17 June 2009.

Abstract - A selection of ten uni- and multivariate, nonparametric statistical methods thought to be useful for assessing trends in indicators estimated from trawl surveys is described. Nonparametric methods make minimal assumptions about the data and can therefore be suitable when parametric modelling methods, as typically preferred by fisheries scientists, are not suitable. The various methods described are sensitive to a variety of specific features of a trend thereby allowing many different forms of variation over time to be identified, e.g. changes in level, sloping straight or curved lines, and differing cyclicities. In contrast, model-based investigations can be constrained in this regard if the single model which is adopted and fitted to the trend is a simplification of its form.

Key words: Quantiles / Runs test / Mann-Kendall statistic / Spearman correlation / Jonckeere test / Nonparametric slope estimator / Cochran Q / Aligned rank test / Dietz-Killeen multivariate trend test

Corresponding author: john.cotter@fishworldscience.com

© EDP Sciences, IFREMER, IRD 2009

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