Natural mortality rated during life history stages on the Red Gruper on Campeche Bank, Mexico

Abstract

The objective of this study was to arrive at biologically convincing estimates of the natural mortality rate (M) for different life history stages of the red grouper Epinephelus morio on Campeche Bank, Mexico. Estimates of M must be compatible with our knowledge of life histories and are essential as input to analytical assessment models for any exploited stock. Because of difficulties in estimating M directly, M has often been incorrectly assumed to be constant with age for a fishery harvesting different age-groups. The gnomonic interval method (GIM) was applied to this long-lived species to estimate a vector of M-values for successive life history stages. The GIM estimates the vector of M at age from the duration of successive development stages and the mean annual fecundity. Estimates were calibrated using available independent data. We computed the relationship between M and age (t) over a 13-year period as Mt = 0.8976t−0.93. Values of M estimated by GIM for adult red grouper were not significantly different (P > 0.05) from those reported in the literature.