A delay difference model as an approach to and simplification of the Deriso-Schnute model (Delay Difference Model) for the case when F and M are constant per time unit
Keywords:Delay Difference Model, aggregated models, stock assessment
The theoretical development of a delay difference model as an approach to and simplification of the Deriso-Schnute model for the case when natural and fishing mortality are constant per time unit and operate simultaneously along the year is presented. The model is derived from Pope’s generalized cohort equation. In the model obtained, fishing mortality is expressed as total annual catches, which simplifies calculations by not having to solve Baranov’s catch equation which is nonlinear with respect to F and that, to obtain the fishing mortality rates corresponding to a given catch level, has to be frequently solved during the process of parameter, projection and risk analysis estimation. In the model proposed, to obtain different fishing instantaneous mortality rates, the assumption of the Deriso-Schnute model that considers that they must be equal for all ages recruited is relaxed. Results are shown in an application example with whitemouth croaker (Micropogonias furnieri) data.
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Copyright (c) 2015 Daniel Hernández
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