Incorporating cannibalism and inter-species predation effects into the hake assessment model: Methods and some preliminary results

Ross-Gillespie, Andrea; Butterworth, Doug S

Incorporating cannibalism and inter-species predation effects into the hake assessment model: Methods and some preliminary results

Working Paper

2013

Publisher

University of Cape Town

Department

Marine Resource Assessment and Management Group

Faculty

Faculty of Science

Abstract

Hake cannibalism and inter-species predation is modelled explicitly using a Type II functional response. Because of the fast dynamics of predation compared to other processes, the standard hake assessment model is converted from a yearly to a monthly time-step. Convergence of model fits is difficult to achieve both because of providing good estimates for starting values and of the tendency of the model towards oscillating behaviour. Thus far satisfactory fits have been obtained only from a somewhat reduced level of predation compared to that thought to occur. These results suggest that both hake species are at higher levels relative to pristine than for the standard assessment.