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HAMMILL, M.O., B. FERLAND-RAYMOND, L.-P. RIVEST, G.B. STENSON, 2009. Modelling Northwest Atlantic Harp Seal populations : modifying an Excel model to R ; Modélisation des populations de phoques du Groenland du Nord-Ouest de l'Atlantique : modification d'un modèle Excel en R. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2009/108, 15 p .
The model currently used to describe the population dynamics of the Northwest Atlantic harp seal (Pagophilus groenlandicus) is a two parameter model that uses information on age specific reproductive rates, ice-related mortality of young seals, removals and estimate of pup production. Although the basic model has taken a number of forms, in recent years it has been run using Excel as a basis. However, the current framework is very slow reducing the opportunities for testing different scenarios and management approaches. In order to improve performance, the model was transferred to R which allowed a reduction in the simulation processing time. During the transfer process, the model was also modified slightly, including a change to the resampling process of pregnancy rates to include correlation among age classes within a year. The R model also builds a new removal matrix for each Monte Carlo simulation using the modeled population age structure rather than the fixed age structure used previously. The Excel and the R models produced similar population trends, but the R model consistently estimated higher populations with a slightly smaller variance. This resulted from the elimination of negative age classes and by the optimisation process that produced lower mortality rates with a smaller variance. The lower variance resulted in higher L20 projections in the R model predictions.
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