Using Indian Ocean swordfish-specific longline data, this paper explores some of the possible deficiencies of the most commonly used method (GLM method) for estimating an index of abundance and then answers two questions: 1) When estimating an index of abundance, can a structural equation model provide a viable alternative to the common GLM method? 2) How do the estimates derived from the GLM method and SEM method contrast? We discover that, at least for this data set, SEM-based methods consistently produce estimates for abundance that are significantly different from those produced by GLM-based methods. Considering the fundamental importance currently ascribed to the GLM-based methods for fisheries management, it is argued that further investigation of SEM-based methodologies is of high priority.
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