Journal Article

Using external information and GAMs to improve catch-at-age indices for North Sea plaice and sole

G. J. Piet

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 59, issue 3, pages 624-632
Published in print January 2002 | ISSN: 1054-3139
Published online January 2002 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1006/jmsc.2002.1184
Using external information and GAMs to improve catch-at-age indices for North Sea plaice and sole

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External information and Generalized Additive Models (GAMs) are used to improve the indices provided by the BTS survey for the stock assessment of plaice and sole. These ancillary data consist of the following variables: Depth, Sediment grain-size, Surface temperature, Latitude, Longitude, Time of day and Day of year. Three approaches that predict the catches of four age-groups of plaice (1–4+) and sole (1–4+) were studied: (1) a “basic” GAM that incorporated the external variables; (2) A GAM where the catches of fish species other than the two target species were represented by three Principal Components (PC's) and added to the “basic” model; (3) The predictions of the basic model were applied to a regular grid covering a slightly expanded index area.

The results are validated using two criteria: one is that of internal consistency, the other compares the estimates with the results of the stock assessments of plaice and sole without the tuning of the BTS index. Both in terms of internal consistency and correlation with the stock assessments all three methods involving GAMs performed better than the actual observed catches. The approach where the predictions of the basic model were applied to a grid performed best of all for both plaice and sole. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.

Keywords: tuning indices; survey data; depth; sediment grain size; diel variation

Journal Article.  0 words. 

Subjects: Environmental Science ; Marine and Estuarine Biology

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