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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on June 13, 2007
ICES Journal of Marine Science: Journal du Conseil 2007 64(5):1028-1032; doi:10.1093/icesjms/fsm077
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© 2007 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Detecting sampling outliers and sampling heterogeneity when catch-at-length is estimated using the ratio estimator

Joël Vigneau1, and Stéphanie Mahévas2

1 IFREMER, Avenue du Général de Gaulle, 14520 Port-en-Bessin, France
2 IFREMER, rue de l'ile d'Yeu, 44311 Nantes, France

Correspondence to J. Vigneau: tel: +33 231 515600; fax: +33 231 515601; e-mail: joel.vigneau{at}ifremer.fr

Vigneau, J., and Mahévas, S. 2007. Detecting sampling outliers and sampling heterogeneity when catch-at-length is estimated using the ratio estimator. – ICES Journal of Marine Science, 64: 1028–1032.

Measuring fish on board fishing vessels or at fish markets to collect data for stock assessment purposes is one of the most straightforward actions carried out by fisheries scientists worldwide. However, such samples are not straightforward to handle and analyse because of their vector-type structure. A generic tool that allows investigation in any multinomial-like sampling scheme is provided, as long as the scheme is built on a ratio estimator, which is the case for most length sampling in the fisheries sector. The use of this tool is discussed using data obtained from two different sampling designs, one consisting of commercial market samples by category and the other on fishing activity or métier. The identification of outliers, misallocated samples, or potential bias as well as the analysis of heterogeneity within and between strata are discussed. The objective of such exploratory analyses is to help sampling coordinators design the best sampling scheme and improve the quality of input data for stock assessment models. The statistics described here are easy to implement and their use is recommended as a necessary stage before any use of sampling data at an international level.

Keywords: length structure, market sampling, sampling design, stratification

Received 6 October 2006; accepted 30 April 2007; advance access publication 13 June 2007.


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