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Issue Aquat. Living Resour. Volume 22, Number 2, April-June 2009 Fish Stock Assessments Using Surveys and Indicators Page(s) 165 - 171 DOI 10.1051/alr/2009018 Published online 17 June 2009

Aquat. Living Resour. 22 (2009) 165-171
DOI: 10.1051/alr/2009018

A multivariate indicator to monitor changes in spatial patterns of age-structured fish populations

Pierre Petitgas and Jean-Charles Poulard

IFREMER, Dép. Ecologie et modèles pour l'halieutique, EMH, BP 21105, 44311 Nantes Cedex 3, France

Received 12 September 2008; Accepted 23 January 2009; Published online 17 June 2009.

Abstract - Quantitative analysis of the spatial patterns in age-structured fish populations provides a useful complement to stock assessment methods. The spatial distribution of an age-structured population is characterized by indicators for location, dispersion and aggregation, which are estimated from survey data. The times series of spatial indicators are organised in a 3D data structure with dimensions along indicators, age classes and years. Multi factor analysis (MFA) is applied to quantify the reproducibility in time of the multivariate structure between age classes and indicators. MFA computes the mean annual pattern over the age classes. The deviation around that pattern in each year is also quantified. A multivariate indicator that characterise the spatial pattern over all age classes is developed. Its variation in time is evaluated with quality control methods. The multivariate indicator is shown to be distributed and a CUSUM control chart is used to detect any significant changes in time. Software for implementing the method is presented and described. To illustrate this new method, North Sea cod data are analysed, and changes in the spatial patterns of the age-structured population are detected and interpreted.

Key words: Multi factor analysis / CUSUM / Monitoring / Spatial distribution

Corresponding author: pierre.petitgas@ifremer.fr

© EDP Sciences, IFREMER, IRD 2009

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