Population dynamics and yield-per-recruit assessment of southwest Florida stone crabs, Menippe mercenaria

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Nelson M. Ehrhardt, Committee Chair


Despite the commercial importance of the stone crab fishery, few studies have been carried out to assess whether current management regulations provide for an adequate utilization of the resource.The major factor contributing to this lack of assessment is that crabs are returned to the ocean after declawing to allow for claw regeneration and increased future harvests. Standard models for stock assessment are inadequate for use with stone crab data because they cannot account for survival and claw regeneration.The goal of this study was to investigate the likely effect of changes in some management regulations. For this purpose, an analytical framework was developed to work out the effects of claw regeneration and survival. In building this framework, relevant information was obtained from the literature or existing data and expressed in analytical form. When necessary, new models were formulated to mimic the species' dynamics.Studies of reproduction data indicated that females can extrude vast numbers of eggs during their lifetime and that declawing may not adversely affect the capability of egg extrusion. A new method to estimate growth was used, suggesting that males and females are fully recruited to the fishery at ages 3 and 5, respectively. A model developed to account for crab survival indicated that standard models can underestimate fishing mortality rates.The models of reproduction, growth and mortality were combined into a computer simulation for yield, value and egg-per-recruit assessment. Analyses were carried out allowing for large uncertainty in input mortality parameters. Results using the best parameter estimates revealed an opportunity for per-recruit gains in yield and value through a reduction in the current minimum size, without significant losses in egg production. However, per-recruit changes could be minimal, or even negative, if current estimates of natural mortality were positively biased and/or in the presence of a strong size selection curve.Knowledge of the accuracy of mortality estimates are necessary to gain precision on the results obtained from the analyses.


Biology, Oceanography; Engineering, Marine and Ocean; Agriculture, Fisheries and Aquaculture

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