Ontogenetic Changes in Natural Mortality Rate of Queen Conch, Strombus Gigas (Mollusca: Mesogastropoda)

The relationship between instantaneous rate of natural mortality (M) and age (t) in queen conchs was modeled using a Weibull hazard function. Data were obtained from the literature. The resulting relationship, M = 4.001t0.0774-1, was highly significant, accounting for over 90% of the variability in the data. The model predicts that mortality rate decreases substantially with age until the onset of sexual maturity. Some implications of the model on assessments in fisheries and mariculture are as follows: (1) in yield-per-recruit analyses, models that allow for variable mortality are preferable, and results of previous analyses are questionable; (2) predictions of mortality for unprotected juveniles can be made and used to design and assess possible mariculture grow-out strategies; and, as an example of the latter, (3) the high rates of mortality noted in field-release experiments using laboratory-reared juveniles are consistent with the model, thus confirming that those release methodologies do not represent viable grow-out strategies.