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Detecting environmental regimes in fish stock-recruitment relationships by fuzzy logic

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A fuzzy logic approach is developed to model and test the impact of environmental regimes on fish stock–recruitment relationships. Traditional methods use environmental variables to classify stock–recruitment data into different membership percentiles followed by fitting the stock–recruitment models for each subset. In contrast, the fuzzy logic approach uses a continuous membership function to provide a rational basis for the classification. Thus, parameter estimation is based on a more logically consistent foundation without resorting to subjective partitions. This new approach is applied to herring stock from the west coast of Vancouver Island (Clupea harengus pallasi) using sea surface temperature as the environmental variable and to Pacific halibut stock (Hippoglossus stenolepis) using the Pacific Decadal Oscillation as the environmental variable. From these applications, the herring stock–recruitment relationships were found to vary significantly during different regimes, whereas this was not the case for halibut. However, in both instances, the fuzzy logic approach demonstrated that density-dependent effects differed between regimes. The fuzzy logic model consistently outperformed traditional approaches as measured by several diagnostic criteria. Because fuzzy logic models address uncertainty better than traditional approaches, they have the potential to improve our ability to understand factors influencing stock–recruitment relationships and thereby manage fisheries more effectively.

Une approche basée sur la logique floue a servi à modéliser et tester l'impact des régimes environnementaux sur les relations entre le stock et le recrutement chez les poissons. Les méthodes traditionnelles utilisent les variables de l'environnement pour classifier les données de stock–recrutement en classes d'appartenances en centiles pour ensuite ajuster les modèles de stock–recrutement à chaque sous-ensemble. Au contraire, l'approche fondée sur la logique floue utilise une fonction continue d'appartenance qui fournit une base rationnelle pour la classification. L'estimation des paramètres est alors basée sur un fondement logique plus solide, sans qu'il soit nécessaire d'avoir recours à des divisions subjectives. Cette nouvelle approche a permis d'étudier le stock de harengs de la côte occidentale de l'île de Vancouver (Clupea harengus pallasi) en utilisant la température de surface de la mer comme variable de l'environnement, ainsi que le stock du flétan du Pacifique (Hippoglossus stenolepis) en prenant l'oscillation décennale du Pacifique comme variable du milieu. Ces analyses ont révélé que les relations stock–recrutement chez le hareng varient de façon significative d'un régime à un autre, mais pas chez le flétan. Cependant, dans les deux cas, l'approche basée sur la logique floue démontre que les effets dépendants de la densité varient selon les régimes. Le modèle basé sur la logique floue s'est révélé plus performant que les approches traditionnelles, d'après plusieurs critères diagnostiques. Parce que les modèles basés sur la logique floue intègrent mieux l'incertitude que les méthodes traditionnelles, ils peuvent améliorer notre capacité de comprendre les facteurs qui influencent les relations stock–recrutement et ainsi de mieux gérer les pêches commerciales.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2001-11-01

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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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