Steepness is a slippery slope

The Beverton–Holt and Ricker stock-recruit functions were derived in terms of two pre-recruit mortality parameters. Mace, & Doonan, (1988, A generalized bioeconomic simulation model for fish population dynamics) reparameterized the function steepness, which combines with post-recruit biological parameters defining unfished spawning biomass per recruit. Their parameterization explicitly assumes a stable age distribution at unexploited conditions, but also implicitly that recruit is time invariant. Temporal variation could occur either rates or parameters, different dynamics are produced. former results both curve equilibria, whereas latter only changes points equilibria on curve. Thus, pre- will result maximum sustainable yield associated management reference points. Empirical measures components productivity (maturity mass age, e.g.) available many managed stocks often exhibit temporal variability. Yet use steepness requires an analyst to specify one set define full series. This misspecification leads misperception has implications meta-analyses interpretation dynamic concept. Returning original allows isolation any inter-population reduces potential mechanistic bias