Examination of a Length-Based Population Analysis

Examination of a Length-Based Population Analysis

T. Matsuishi

Examination of a Length-Based Population AnalysisThis is part of Fishery Stock Assessment Models
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Virtual population analysis (VPA) and cohort analysis are widely used for estimating fish population size from catch-at-age data. Generally age determination is so laborious that catch-at-age is often determined from catch-at-length data. Errors in this conversion, however, can be significant.

Fishery managers often control the selectivity of fishing gear. To manage fish stocks, the managers need population-at-length estimates instead of population-at-age. Another conversion is needed to estimate population-at-length from population-at-age, which is calculated from catch-atage using VPA. Estimation errors in this conversion can also be significant. If population at length can be estimated directly from catch-at-length, these two conversions can be omitted, and thus the estimation accuracy will be improved.

In this study, I utilize a method of population estimation based on catch-at-length called Length-based Population Analysis or LPA. LPA estimates population-at-length from the largest to the smallest length class, by avoiding the estimation errors of recruitment. I also examine the validity and accuracy of LPA using computer simulation, and present the result of two applications.

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