Abstract
Abstract Beverton and Holt’s (1957. On the dynamics of exploited fish populations. UK Ministry of Agriculture, Fisheries and Food. Fisheries Investigations, 2: 533 pp.) monograph contributed a widely used stock–recruitment relationship (BH-SRR) to fisheries science. However, because of variation around a presumed relationship between spawning biomass and recruits, the BH-SRR is often considered inadequate and approached merely as a curve-fitting exercise. The commonly used and simplified version of the BH-SRR has eclipsed the fact that in their classic monograph, the derivation accounted for mechanistic recruitment processes, including multi-stage recruitment with explicit cohort-dependent and -independent mortality terms that represent competition between recruits and extrinsic, cohort-independent factors such as the environment or predation as two independent sources of mortality. The original BH-SRR allows one to recreate recruitment patterns that correspond to observed ones. Doing so shows that variation in density-independent mortality increases the probability of overlooking an underlying stock–recruitment relationship. Intermediate coefficients of variation in mortality (75–100%) are sufficient to mask stock–recruitment relationships and recreate recruitment time series most similar to empirical data. This underlines the importance of variation in survival for recruitment and that Beverton and Holt’s work still provides a fundamental and useful tool to model the dynamics of populations.
Highlights
In the population dynamics of fish, recruitment is both a key process and a major source of uncertainty due to its large variability, often over several orders of magnitude (Shepherd et al, 1990; Hilborn and Walters, 1992)
Fundamental biological principles require that recruitment is linked to the spawning stock size (Myers and Barrowman, 1996; Vert-pre et al, 2013; Zimmermann et al, 2018), in most stocks the stock–recruitment relationship (SRR) explains only a minor proportion of recruitment variability (Cury et al, 2014; Munch et al, 2018)
The empirical relevance of SRRs has been increasingly dismissed despite their continued conceptual relevance (Rose et al, 2001; Szuwalski et al, 2015; Szuwalski et al, 2019) [which has been reflected in stock assessments when, for instance, steepness is set at or close to 1 and recruitment is assumed to be entirely or largely independent of stock size, see e.g. Aires-daSilva and Maunder (2007) and Maunder (2012)]
Summary
In the population dynamics of fish, recruitment is both a key process and a major source of uncertainty due to its large variability, often over several orders of magnitude (Shepherd et al, 1990; Hilborn and Walters, 1992). In their 1957 monograph, Ray Beverton and Sidney Holt treated recruitment as densitydependent process (Beverton and Holt, 1957), resulting in a seminal stock–recruitment relationship (SRR) that has since remained widely used in the modelling of fisheries. Pre-recruits are subject to often very different sources of mortality across stage that may exhibit differences in their variance
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