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A comparison of gamma and lognormal maximum likelihood estimators in a sequential population analysis

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We analyze the model used to assess most major commercial marine fish populations, namely, sequential population analysis (SPA). This model estimates population abundance by combining catch-at-age data with research surveys or commercial catch per unit effort indices of abundance. We examine two maximum likelihood estimators of SPA parameters. These estimators are based on assuming that the stock-size indices are from lognormal or gamma distributions. Using simulations, we find that both types of estimators can have significant biases; however, our results indicate that it is preferable to use the gamma model, because it tends to have lower bias and variability, even when the true distribution of the stock-size indices is lognormal.

On trouvera ici un examen de l'analyse séquentielle de population (SPA), le modèle qui est utilisé pour évaluer la plupart des populations de poissons marins d'intérêt commercial. Ce type de modèle estime l'abondance de la population en combinant des données sur la capture à chacun des âges à des indices d'abondance basés sur des inventaires scientifiques ou sur le succès de la pêche commerciale par unité d'effort. Deux estimateurs de vraisemblance maximale des paramètres de la SPA ont été comparés; les deux estimateurs supposent que les indices de densité des stocks sont tirés de distributions lognormales ou gamma. Des simulations montrent que les deux types d'estimateurs peuvent introduire des erreurs systématiques importantes; cependant, d'après ces résultats, il est préférable d'utiliser le modèle gamma car il introduit moins de biais et de variation, même lorsque la véritable distribution des indices de densité des stocks est lognormale.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2001

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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