Evaluation of logistic surplus production model through simulations

Abstract

A simulation study was conducted to evaluate the reliability of estimates of maximum sustainable yield (MSY), the biomass at which the MSY is obtained (Bmsy), the exploitation rate required to achieve the MSY (Emsy), and the intrinsic population growth rate (r), from a logistic production model fitted to catch and catch-rate data generated from an age-structured model. Both process (recruitment) and observation errors were considered. Natural mortality rate (M) and stock–recruitment steepness (h) values were used to construct productivity scenarios. Virtually all MSY estimates were between 50% and 150% of the “true”MSY values, although the Bmsy and Emsy were largely over- and under-estimated, respectively, in the absence of process and observation error. The MSY estimates were still reasonably accurate, but less reliable when h was low (<0.45) in the presence of process and observation error. About 87% of the MSY estimates were between 50% and 150% of the “true”MSY values when the coefficient of variation for the process and observation errors were both 30% (30–30% case), while 60% of the MSY estimates were between 50% and 150% of the “true”MSY values for the 80–30% case. Overestimation of MSY increased with increasing process error. The probability of overestimation of MSY increased from 0.59 (30–30% case) to 0.85 (80–30% case), suggesting that caution is needed when using an estimate of MSY from the logistic production model to design a management plan, especially for populations with low productivity. Bmsy was more likely overestimated and Emsy was, in general, conservatively estimated. The estimates of Bmsy and Emsy seemed to be useful for a benchmark for evaluation of the stock status and for selecting harvesting intensities, respectively.