An individual-based approach to year-class strength estimation

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Estimating year-class strength—the number of larvae hatched in a given year—from survey data is key to investigating fish population dynamics. Year-class strength can be estimated from catch-at-age data using catch curves. In practice, most catch-curve assumptions are violated, which can result in spurious estimates of year-class strength. Among the simplifying assumptions is that pooling individuals into annual age-classes provides a representation of the population age structure that is adequate for estimating mortality. This oversimplification is unnecessary when age data are available at finer scales, and can lead to biased results. We present a new method to estimate past year-class strength with a set of equations that apply to each sampled individual. Through the reconstruction of individual histories from hatch to capture, this approach takes full advantage of the individual resolution of survey data, enables the incorporation of the processes that violate catch-curve assumptions, and provides more accurate year-class strength estimates.

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