An individual-based approach to year-class strength estimation

Abstract

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.

Longitudinal analyses of catch-at-age data for reconstructing year-class strength, with an application to lake trout (Salvelinus namaycush) in the main basin of Lake Huron

“…This modeling approach can be distinguished from more comprehensive fishery stock assessment models that calculate absolute abundances of fish year-classes and estimate mortality rates, such as virtual population analyses (Shepherd and Pope 2002) and statistical catch-at-age (SCAA) models (Maunder and Punt 2013;Methot and Wetzel 2013;Aeberhard et al 2018), which require data on total removals and often rely on additional data and assumptions (Ricker 1975;Hilborn and Walters 1992;Maunder and Deriso 2003). There are also other approaches to estimating YCS based on assumptions of fish mortality, such as using residuals of catch-curve regressions (Maceina 1997;Tetzlaff et al 2011) or individual-based approaches of population modeling (Thanassekos et al 2016). In contrast, the YCS model that we generalize in this paper is a statistical description of indices from catch-at-age data.…”